Requirements for Flood Openings
in Foundation Walls and Walls
of Enclosures
Below Elevated Buildings in Special Flood Hazard Areas
In Accordance with the National Flood Insurance Program
NFIP Technical Bulletin 1 / March 2020
Comments on the Technical Bulletins should be directed to:
Department of Homeland Security / Federal Emergency Management Agency
Federal Insurance and Mitigation Administration (FIMA) Risk Management Directorate
Building Science Branch
400 C Street, S.W., Sixth Floor
Washington, DC 20472-3020
NFIP Technical Bulletin 1 (2020) replaces NFIP Technical Bulletin 1 (2008), Openings in Foundation Walls
and Walls of Enclosures.
Photograph credits:
Cover: Leigh Chapman, Salters Creek Consulting
Figure 3. Bill Bryant, Anne Arundel County, Maryland
Figure 17. North Carolina Emergency Management/T. Riddle
NFIP Technical Bulletin 1 contains information that is proprietary to and copyrighted by the American
Society of Civil Engineers and information that is proprietary to and copyrighted by the International Code
Council, Inc.All information is used with permission.
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NFIP TECHNICAL BULLETIN 1 MARCH 2020
i
Table of Contents
Acronyms .............................................................................................................................................................iv
1 Introduction ......................................................................................................................................................1
2 National Flood Insurance Program Regulations ............................................................................................... 3
3 Building Codes and Standards ......................................................................................................................... 5
3.1 International Residential Code .............................................................................................................5
3.2 International Building Code and ASCE 24 ..........................................................................................6
4 NFIP Flood Insurance Implications ...................................................................................................................8
5 Documenting Building Elevations and Flood Openings Using the NFIP Elevation Certificate ..........................8
6 Use of Enclosed Areas Below Elevated Buildings ............................................................................................9
7 Foundation Walls and Enclosure Walls that Require Flood Openings ............................................................ 10
7.1 Solid Perimeter Foundation Walls (Crawlspacesand Under-Floor Spaces) .....................................11
7.2 Solid Perimeter Foundation Walls (Below-Grade Crawlspaces) .......................................................12
7.3 Garages Attached to Elevated Buildings ............................................................................................13
7.4 Enclosed Areas Under Buildings Elevated on Open Foundations ................................................... 14
7.5 Enclosed Areas with Breakaway Walls Under Buildings Elevated on Open Foundations ..............15
7.6 Above-Grade (Elevated) Enclosed Areas ............................................................................................16
7.7 Two-Level Enclosed Areas ................................................................................................................... 17
7.8 Solid Perimeter Foundation Walls on which Manufactured Homes Are Installed .........................18
7.9 Accessory Structures ............................................................................................................................19
8 Requirements and Guidance for Installation of Flood Openings ....................................................................20
8.1 Location and Minimum Number of Flood Openings .......................................................................20
8.2 Height of Flood Openings Above Grade or Floor .............................................................................21
8.3 Examples of Flood Opening Installations .......................................................................................... 22
8.3.1 Interior Grade or Floor Higher than the Exterior Grade ....................................................22
8.3.2 Sloping Sites .............................................................................................................................23
8.3.3 Buildings with Large Enclosed Areas.....................................................................................24
8.3.4 Townhouses with Limited Exterior Walls ..............................................................................24
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NFIP TECHNICAL BULLETIN 1 MARCH 2020
8.3.5 Buildings with Multiple Enclosures ........................................................................................ 25
8.3.6 Flood Openings in Areas with Shallow Flooding ..................................................................26
9 Non-Engineered Flood Openings and Engineered Flood Openings ................................................................ 27
9.1 Measures Not Acceptable as Flood Openings ....................................................................................28
9.2 Non-Engineered Flood Openings .......................................................................................................28
9.3 Engineered Flood Openings ...............................................................................................................33
9.3.1 Design and Performance Requirements ................................................................................33
9.3.2 Documentation of Engineered Openings for Compliance ..................................................36
9.3.3 Engineered Openings with Certification Reports ................................................................36
9.3.4 Engineered Openings Individually Certified for Specific Buildings ................................... 37
9.3.5 NFIP Elevation Certificate and Documentation of Engineered Openings for Flood
Insurance .................................................................................................................................39
10 References .....................................................................................................................................................41
List of Figures
Figure 1: Equalizing flood forces (hydrostatic loads) on exterior walls .......................................................1
Figure 2: Typical enclosures with flood openings in Zone A ........................................................................2
Figure 3: Full-height, solid perimeter walls surrounding a garage and storage area with flood
openings .......................................................................................................................................... 11
Figure 4: Backfilled stem wall foundation; flood openings not required ...................................................12
Figure 5: Limitations on below-grade crawlspaces in shallow flood hazard areas .....................................13
Figure 6: Engineered openings in garage doors .......................................................................................... 14
Figure 7: Enclosure with flood openings under a house elevated on pilings .............................................15
Figure 8: Above-grade enclosures.................................................................................................................. 17
Figure 9: Two-level enclosure with non-load-bearing walls under building elevated on pilings or
columns; configuration also applies if walls are load-bearing ....................................................18
Figure 10: Manufactured home supported on interior piers and masonry perimeter wall with
flood openings ................................................................................................................................ 19
Figure 11: Foundation plan of home with multiple enclosed areas, each with flood openings .................21
Figure 12: Manufactured home installed on columns above a full-height, framed garage (note
elevation of thick driveway slab on left; the flood openings are within 1 foot of interior
floor surface) ..................................................................................................................................22
Figure 13: Flood openings in enclosure walls on a sloping site ....................................................................23
Figure 14: Flood openings that are stacked and closely grouped to satisfy the required total net
open area .........................................................................................................................................24
NFIP TECHNICAL BULLETIN 1 MARCH 2020
iii
Figure 15: Suggested flood openings in enclosures under elevated townhouses ........................................25
Figure 16: Bottom of the flood opening positioned as close as possible to grade (or floor) when
any portion of the opening extends above the BFE ..................................................................... 26
Figure 17: Standard air vent that is unacceptable as a flood opening because it is not disabled in
the open position ............................................................................................................................ 28
Figure 19: Example of non-engineered opening: Typical standard air vent with fixed, angled
blades providing approximately 44 square inches of net open area; measurement of
net open area uses slot width of 13 inches times the sum of the spaces between the blades ....29
Figure 18: Example of non-engineered opening: Typical standard air vent faceplate providing
42 square inches of net open area if disabled in the open position; measurement of net
open area uses a slot width of 0.5 inch times a slot height of 0.65 inch times the total
number of slots ...............................................................................................................................29
Figure 20: Typical air vents with insect screens blocked by flood debris ......................................................30
Figure 21: Examples of typical air vents in crawlspace foundation walls used as flood openings
with varying net open areas ...........................................................................................................31
Figure 22: Decorative masonry units and closely spaced holes in brickwork; the area of each hole
counts toward the total net open area ..........................................................................................32
Figure 23: Concrete blocks turned sideways with insect screening; a typical 8- by 16-inch block
provides approximately 60 square inches of net open area ......................................................... 32
Figure 24: Wood frame with insect screen inserted in void in poured concrete foundation wall;
inside dimensions of frame determine net open area .................................................................33
Figure 25: Equation used to determined total net area of engineered openings ........................................ 34
Figure 26: Completing the NFIP Elevation Certificate when engineered openings are used ....................40
List of Tables
Table 1: Comparison of Selected 2018 IRC and NFIP Flood Opening Requirements ..............................6
Table 2: Comparison of Selected 2018 IBC and ASCE 24-14 Flood Opening Requirements with
NFIP Requirements ..........................................................................................................................7
Table 3: Flood Opening Coefficient of Discharge ...................................................................................... 35
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NFIP TECHNICAL BULLETIN 1 MARCH 2020
Acronyms
ASCE American Society of Civil Engineers
BFE base flood elevation
CFR Code of Federal Regulations
DHS Department of Homeland Security
FEMA Federal Emergency Management Agency
FIRM Flood Insurance Rate Map
IBC International Building Code
®
ICC International Code Council
®
ICC-ES ICC Evaluation Service
I-Codes International Codes
®
IRC International Residential Code
®
LiMWA Limit of Moderate Wave Action
NFIP National Flood Insurance Program
NFPA National Fire Protection Association
SEI Structural Engineering Institute
SFHA Special Flood Hazard Area
NFIP TECHNICAL BULLETIN 1 MARCH 2020
1
1 Introduction
This Technical Bulletin explains the National Flood Insurance Program (NFIP) requirements for flood
openings in foundation walls and walls of enclosures below elevated buildings in Special Flood Hazard
Areas (SFHAs) that are designated as Zone A (A, AE, A1-30, AH, and AO) on Flood Insurance Rate Maps
(FIRMs). The flood opening requirements are intended to equalize hydrostatic forces (loads or pressure
caused by standing or slow-moving water) on walls, thus preventing damage to or collapse of the building
(see Figure 1). The requirements are not intended to reduce flood damage caused by hydrodynamic loads
associated with fast-moving water (e.g., faster than 10 feet per second), wave impacts, or debris impacts.
Figure 1: Equalizing flood forces (hydrostatic loads) on exterior walls
This Technical Bulletin includes the following:
• Examples of foundation walls and enclosure walls that require openings. Figure 2 illustrates typical
enclosures with flood openings in Zone A: a crawlspace foundation wall, a non-load-bearing wood-
framed wall surrounding an enclosed area under a piling- or column-supported building, and a
concrete or masonry load-bearing foundation wall surrounding an enclosed area. Other types of
enclosures or situations may require the advice of a registered design professional.
• Information on installing flood openings, including the minimum number and minimum height
above grade, and examples of installations.
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NFIP TECHNICAL BULLETIN 1 MARCH 2020
• Guidance on prescriptive (non-engineered) and engineered flood openings. Non-engineered
openings do not have moving parts and may be used to meet the NFIP prescriptive requirement
for 1 square inch of net open area for every square foot of enclosed area. Engineered openings
may be used if designed and certified by a registered design professional as meeting certain
performance characteristics.
• Description of how flood openings affect NFIP flood insurance premiums.
• Guidance on documenting building elevations and flood openings using the NFIP Elevation
Certificate (FEMA Form 086-0-33) (FEMA, 2015).
Figure 2: Typical enclosures with flood openings in Zone A
NFIP TECHNICAL BULLETIN 0
NFIP Technical Bulletin 0, User’s Guide to Technical Bulletins, should be used as a reference in
conjunction with this Technical Bulletin. Technical Bulletin 0 describes the purpose and use of the
Technical Bulletins, includes common concepts and terms, lists useful resources, and includes a
crosswalk of the sections of the NFIP regulations identifying the Technical Bulletin that addresses each
section of the regulations and a subject index.
Readers are cautioned that the denitions of some of the terms that are used in the Technical Bulletins
are not the same when used by the NFIP for the purpose of rating ood insurance policies.
Questions about enclosure and flood opening requirements should be directed to the appropriate
local official, NFIP State Coordinating Office, or Federal Emergency Management Agency (FEMA)
Regional Office.
NFIP TECHNICAL BULLETIN 1 MARCH 2020
3
2 National Flood Insurance Program
Regulations
An important NFIP objective is protecting buildings constructed in SFHAs from damage caused by
flooding. The SFHA, composed of Zones A and V, is the areal extent of the base flood shown on Flood
Insurance Rate Maps (FIRMs) prepared by FEMA. The base flood is the flood that has a 1 percent chance
of being equaled or exceeded in any given year (commonly called the “100-year” flood).
The NFIP floodplain management regulations include minimum building design criteria that apply to:
• New construction
• Work determined to be Substantial Improvements, including improvements, alterations, and additions
• Repair of buildings determined to have incurred Substantial Damage
A defining characteristic of the NFIP regulations applicable in Zone A is the requirement for the lowest
floor (including basement) to be elevated to or above the BFE. Non-residential buildings in Zone A must
be elevated or dry floodproofed. The requirements in Zone V, not addressed in this Technical Bulletin,
also specify building elevation, foundation, and enclosure requirements.
Enclosed areas (enclosures) are permitted below elevated buildings if the enclosed areas meet
requirements, including limitations on use (parking of vehicles, building access, or storage), use of flood
damage-resistant materials, and installation of flood openings that allow automatic entry and exit of
floodwater (i.e., free inflow and outflow in both directions) to equalize the hydrostatic flood loads.
NFIP TERMS USED IN THIS TECHNICAL BULLETIN
• Basement: Area of a building that has its oor subgrade (below ground level) on all sides. NFIP
regulations do not allow basements to extend below the base ood elevation (BFE) except in
dry-oodproofed, non-residential buildings.
• Enclosed area (enclosure): An area below an elevated building that is enclosed by walls on all sides.
• Lowest floor: Lowest oor of the lowest enclosed area of a building, including basement. An
unnished or ood-resistant enclosure that is used solely for parking of vehicles, building access,
or storage is not the lowest oor, provided the enclosure is built in compliance with applicable
requirements.
• Net open area: Permanently open area of a non-engineered ood opening.
• Special Flood Hazard Area (SFHA): Area subject to ooding by the base ood (1-percent-annual-
chance ood) and shown on Flood Insurance Rate Maps (FIRMs) as Zone A or Zone V.
• Zone A: Flood zones shown on FIRMs as Zone A, AE, A1-30, AH, AO, A99, and AR.
• Zone V: Flood zones shown on FIRMs as Zone V, VE, V1-30, and VO.
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NFIP TECHNICAL BULLETIN 1 MARCH 2020
The NFIP regulations for enclosures and flood openings are codified in Title 44 of the Code of Federal
Regulations (CFR) Part 60. Specific to NFIP Technical Bulletin 1, 44 CFR § 60.3(c)(5) states that a
community shall:
Require, for all new construction and substantial improvements, that fully enclosed areas
below the lowest floor that are usable solely for parking of vehicles, building access or storage
in an area other than a basement and which are subject to flooding shall be designed to
automatically equalize hydrostatic flood forces on exterior walls by allowing for the entry
and exit of floodwaters. Designs for meeting this requirement must either be certified by a
registered professional engineer or architect or meet or exceed the following minimum
criteria: A minimum of two openings having a total net area of not less than one square inch
for every square foot of enclosed area subject to flooding shall be provided. The bottom of
all openings shall be no higher than one foot above grade. Openings may be equipped with
screens, louvers, valves, or other coverings or devices provided that they permit the automatic
entry and exit of floodwaters.
NFIP REQUIREMENTS AND HIGHER REGULATORY STANDARDS
State or Local Requirements. State or local requirements that are more restrictive or stringent than the
minimum requirements of the NFIP take precedence. The Technical Bulletins and other FEMA publications
provide guidance on the minimum NFIP requirements and describe best practices. Design professionals,
builders, and property owners should contact local ofcials to determine whether more restrictive
requirements apply to buildings or sites in question. All other applicable requirements of state or local
building codes must also be met for buildings in ood hazard areas.
Substantial Improvement and Substantial Damage. As part of issuing permits, local ofcials must
review not only proposals for new construction but also for work on existing buildings to determine
whether the work constitutes Substantial Improvement or repair of Substantial Damage. If the work is
determined to constitute Substantial Improvement or repair of Substantial Damage, the buildings must
be brought into compliance with the NFIP requirements for new construction. Some communities modify
the denitions of Substantial Improvement and/or Substantial Damage to be more restrictive than the
NFIP minimum requirements. For more information on Substantial Improvement and Substantial Damage,
see FEMA P-758, Substantial Improvement/Substantial Damage Desk Reference (2010), and FEMA 213,
Answers to Questions About Substantially Improved/Substantially Damaged Buildings (2018).
Elevation Above Minimum NFIP Requirements. Some communities require that buildings be elevated
above the NFIP minimum requirement. The additional elevation is called freeboard. Design professionals,
builders, and property owners should check with local ofcials to determine whether a community has
freeboard requirements. References to building elevations in this Technical Bulletin should be construed
as references to the community’s elevation requirement where freeboard is required.
Legal Nonconforming Buildings. Owners of older, legal nonconforming buildings that are elevated with
enclosures below the BFE may wish to retrot the enclosures to conform to current requirements for
enclosures, even when the enclosure is below grade on all sides. Lower NFIP ood insurance rates may
apply if retrot enclosures have ood openings that meet the requirements in this Technical Bulletin and
other requirements for enclosures (e.g., limited use, ood damage-resistant materials, elevated utilities).
NFIP TECHNICAL BULLETIN 1 MARCH 2020
5
3 Building Codes and Standards
In addition to complying with the NFIP requirements, all new construction, Substantial Improvements,
and repair of Substantial Damage must comply with the applicable building codes and standards adopted
by states and communities.
The International Codes
®
(I-Codes
®
), published by the International Code Council
®
(ICC
®
), are a family
of codes that includes the International Residential Code
®
(IRC
®
), International Building Code
®
(IBC
®
),
International Existing Building Code
®
(IEBC
®
), and codes that govern the installation of mechanical,
plumbing, fuel gas service, and other aspects of building construction. FEMA has deemed that the latest
published editions of the I-Codes meet or exceed NFIP requirements for buildings and structures in
flood hazard areas. Excerpts of the flood provisions of the I-Codes are available on FEMA’s Building
Code Resource webpage (https://www.fema.gov/building-code-resources).
3.1 International Residential Code
The IRC applies to one- and two-family dwellings and
townhomes not more than three stories above grade
plane. The IRC requirements related to flood openings,
summarized in Table 1, are similar to but generally exceed
NFIP requirements.
Table 1 refers to selected requirements of the 2018 IRC
and notes changes from the 2015 and 2012 editions;
subsequent editions of the IRC should include comparable
requirements.
IRC COMMENTARY
The ICC publishes companion
commentary for the IRC. Although not
regulatory, the commentary provides
guidance that is useful in complying
with, interpreting, and enforcing the
requirements of the code.
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NFIP TECHNICAL BULLETIN 1 MARCH 2020
Table 1: Comparison of Selected 2018 IRC and NFIP Flood Opening Requirements
Topic
Summary of Selected 2018 IRC Requirements
and Changes from 2015 and 2012 Editions
Comparison with NFIP
Requirements
Flood openings
Section R322.2.2(2) Enclosed area below design flood elevation.
Requires enclosed areas below the design ood elevation, including
crawlspaces, to have ood openings (non-engineered or engineered)
that meet listed criteria and that are installed in accordance with
R322.2.2.1. The enclosed area is measured on the exterior of the
enclosure. The listed criteria are equivalent to non-engineered and
engineered openings, with the addition of a minimum size (not less
than 3 inches in any direction in the plane of the wall).
Change from 2015 to 2018 IRC: No change.
Change from 2012 to 2015 IRC: No change.
Equivalent to NFIP
44 CFR § 60.3(c)(5) but
with more specicity:
measurement of
enclosed area and
minimum dimensions of
opening.
Installation of
ood openings
Section R322.2.2.1 Installation of openings.
Species the following for the installation of ood openings:
• At least two openings on different sides of an enclosure are
required, and if more than one enclosed area is present, each must
have openings on exterior walls.
• The bottom of each opening must be not more than 1 foot above the
higher of the nal interior grade (or oor) and the nished exterior
grade immediately under each opening.
• Openings are permitted to be installed in doors and windows.
Change from 2015 to 2018 IRC: No change.
Change from 2012 to 2015 IRC: Installation requirements moved to
new section.
More specicity
than NFIP 44 CFR
§ 60.3(c)(5): openings on
different sides, openings
installed above higher
of interior and exterior
grade or oor, and
openings installed in
doors.
Breakaway
walls
Section R322.3.5 Walls below design flood elevation.
Requires walls below elevated dwellings in Coastal High Hazard Areas
(Zone V) and Coastal A Zones that are intended to break away under
ood loads to have ood openings that meet the requirements of
Section R322.2.2(2).
Change from 2015 to 2018 IRC: Section number was R322.3.4.
Change from 2012 to 2015 IRC: New requirement in Coastal High
Hazard Areas (Zone V) and Coastal A Zones if delineated.
Exceeds NFIP 44 CFR
§ 60.3(e)(5): openings
in breakaway walls and
Zone V requirements
applied in Coastal A
Zones if delineated.
3.2 International Building Code and ASCE 24
The flood provisions of the latest published editions of the IBC meet or
exceed NFIP requirements for buildings, largely through reference to
the standard ASCE 24, Flood Resistant Design and Construction, developed
by the American Society of Civil Engineers (ASCE). The IBC applies
to all applicable buildings and structures. While primarily used for
buildings and structures other than dwellings within the scope of the
IRC, the IBC may be used to design dwellings. ASCE 24 requirements
for flood openings, summarized in Table 2, are similar to but generally
exceed and are more specific than NFIP requirements. Table 2 refers to
selected requirements of the 2018 IBC and ASCE 24-14 (noting changes
from 2015 and 2012 IBC and ASCE 24-05); subsequent editions of the
IBC and ASCE 24 should include comparable requirements.
IBC AND ASCE 24
COMMENTARIES
The ICC publishes
companion commentary
for the IBC, and ASCE
publishes companion
commentary for ASCE 24.
Although not regulatory,
the commentaries
provide guidance that is
useful in complying with,
interpreting, and enforcing
the requirements.
NFIP TECHNICAL BULLETIN 1 MARCH 2020
7
Table 2: Comparison of Selected 2018 IBC and ASCE 24-14 Flood Opening Requirements with NFIP Requirements
Topic
Summary of Selected 2018 IBC/ASCE 24-14 Requirements
and Changes from 2015 and 2012 IBC/ASCE 24-05
Comparison with
NFIP Requirements
Certication
of engineered
openings
Section 1612.4(1.2).
Requires submission of a certication statement that the design provides
for equalization of hydrostatic ood forces in accordance with ASCE 24,
Section 2.7.2.2 (for engineered openings), if ood openings do not meet the
requirements of ASCE 24, Section 2.7.2.1 (for non-engineered openings).
Change from 2015 to 2018 IBC: Section number was 1612.5.
Change from 2012 to 2015 IBC: No change.
Equivalent to NFIP
44 CFR § 60.3(c)(5).
Breakaway
walls
ASCE 24 Section 2.7.1.1.
Requires openings in breakaway walls.
Change from ASCE 24-05: New requirement for openings in breakaway
walls in Coastal High Hazard Areas and Coastal A Zones.
Exceeds
NFIP 44 CFR
§ 60.3(e)(5) by
requiring openings
in breakaway walls.
Non-
engineered
openings
ASCE 24 Section 2.7.2.1.
Species non-engineered openings, requires enclosed areas to be
measured on the exterior, species minimum size (not less than 3 inches
in any direction in the plane of the wall), and requires that the presence
of louvers, blades, screens, faceplates or other covers, and devices be
accounted for in determining net open area.
Change from ASCE 24-05: Species measurement of enclosed areas
to determine square footage. Claries that the presence of louvers,
blades, screens, faceplates, and devices must be accounted for in the
measurement of net open area of ood openings.
Equivalent to
NFIP 44 CFR
§ 60.3(c)(5) but with
more specicity:
measurement of
enclosure area,
minimum dimension
of openings, and
measurement of net
open area.
Engineered
openings
ASCE 24 Section 2.7.2.2.
Species engineered openings with emphasis on performance accounting
for the presence of louvers, blades, screens, grilles, faceplates or other
covers, and devices and ensuring that the difference between exterior
and interior ood levels does not exceed 1 foot, with guidance related to
the rate of rise and fall in excess of (or less than) 5 feet per hour. Species
minimum size (not less than 3 inches in any direction in the plane of the
wall). Provides the formula for calculating the total net area of required
engineered openings.
Change from ASCE 24-05: Greater emphasis on performance and the
effects of louvers, blades, screens, grills, faceplates, and devices and
revises the table of coefcients of discharge
Equivalent to
NFIP 44 CFR
§ 60.3(c)(5) but with
more specicity:
minimum rate
of rise and fall,
minimum dimension
of openings,
and formula
for engineered
openings.
Installation of
ood openings
ASCE 24 Section 2.7.3.
Species the following for the installation of openings:
• At least two openings in at least two walls of each enclosed area
• The bottom of each opening not more than 1 foot above the higher of the
nal interior grade or oor and the nished exterior grade immediately
under each opening
• Openings in doors and windows permitted
Change from ASCE 24-05: Consolidates installation requirements, which
apply to both non-engineered and engineered openings, and claries that
the position is relative to the higher of the interior and exterior grade or oor.
Equivalent to
NFIP 44 CFR
§ 60.3(c)(5) but with
more specicity:
openings on
different sides,
bottom of openings
above higher of
interior and exterior
grade or ood, and
openings in doors
and windows.
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NFIP TECHNICAL BULLETIN 1 MARCH 2020
4 NFIP Flood Insurance Implications
Careful attention to compliance with NFIP requirements for enclosures below elevated lowest floors and
flood openings is important during the design, plan review, construction, and inspection of buildings in
SFHAs. Compliance influences vulnerability to flood damage and also the cost of NFIP flood insurance
policies. The presence of enclosures may result in higher NFIP flood insurance premiums. If flood
openings are not compliant, the floor of a crawlspace or the floor of an enclosure will be deemed the
lowest floor for insurance rating purposes, which may result in higher NFIPflood insurance premiums,
especially if the floor of the crawlspace or enclosure is more than 1 foot below the BFE.
5 Documenting Building Elevations
and Flood Openings Using the NFIP
Elevation Certificate
Communities are required to obtain the following from permit holders for buildings in SFHAs: the
surveyed elevation of lowest floors of new buildings and buildings that have been Substantially Improved
or repaired after incurring Substantial Damage. The elevations may be provided on the NFIP Elevation
Certificate or in other formats.
The NFIP Elevation Certificate is designed to facilitate the collection of information that will help local
officials evaluate compliance with floodplain management requirements and to provide the information
necessary for the proper rating of NFIP flood insurance policies. For guidance on completing the
certificate, see NFIP Elevation Certificate and Instructions (FEMA, 2015) and FEMA 467-1, Floodplain
Management Bulletin: Elevation Certificate (FEMA, 2004).
The required information includes the following
characteristics of crawlspaces, enclosures, and
attached garages:
• Square footage of the enclosed area, measured
on the outside of the enclosure walls
• Number of permanent flood openings within
1.0 foot above adjacent grade
• Total net open area of flood openings
• Whether engineered openings are used
According to the NFIP Elevation Certificate
instructions, when an enclosed area has no flood
openings or if all flood openings (non-engineered
NFIP ELEVATION CERTIFICATE COMMENTS
The comment section of the NFIP Elevation
Certicate should be used to note
characteristics of enclosures and ood
openings that comply with the requirements but
that, without close inspection, may appear to be
non-compliant. In particular, without clarifying
comments on engineered openings, local
ofcials and insurance agents may inadvertently
determine that enclosures are non-compliant
and deem the oor of the enclosure the lowest
oor, resulting in unnecessarily high NFIP ood
insurance premiums.
NFIP TECHNICAL BULLETIN 1 MARCH 2020
9
or engineered) are higher than 1.0 foot above the adjacent grade, “N/A” (not applicable) should be
entered for both the number of flood openings within 1.0 foot above adjacent grade and total net open
area of flood openings. If the bottoms of some flood openings are within 1.0 foot above the adjacent
grade, only the number and net open area of those openings should be recorded (openings that are
higher than 1.0 foot are not included).
The certificate does not require users to determine whether any portion of a flood opening is above the
BFE. However, for compliance purposes, see Section 8.3.6 of this Technical Bulletin for guidance on
flood openings that extend above the BFE, which can occur in areas with shallow flooding. In these areas,
even if the bottom of an opening is less than 1.0 foot above grade, a portion of the opening may extend
above the BFE.
The NFIP Elevation Certificate has space for comments. Comments must be entered when engineered
openings are used. Section 9.3.2 of this Technical Bulletin describes the documentation that is required
for engineered openings and that must be attached to the certificate.
6 Use of Enclosed Areas Below Elevated
Buildings
The NFIP regulations specify that enclosed areas under
elevated buildings in SFHAs may be allowed if the enclosed
areas are used solely for:
• Parking of vehicles (attached garages or parking areas
below elevated buildings)
• Building access (stairwells, foyers)
• Storage (recommended to be limited to storage of low-
value items)
The NFIP regulations do not list crawlspaces and under-floor
spaces as allowable uses of enclosed areas. However, buildings
in Zone A may be elevated using perimeter foundation walls
that create these enclosed areas. Crawlspaces and under-
floor spaces provide access to under-floor utilities such as
pipes, ductwork, and electric conduits.
DRY FLOODPROOFED BUILDINGS
The only buildings with enclosed
areas that are not required to have
ood openings are non-residential
buildings that are engineered to be
dry oodproofed. For information on
dry oodproong, see FEMA P-936,
Floodproofing Non-Residential
Buildings (FEMA, 2013), and NFIP
Technical Bulletin 3, Non-Residential
Floodproofing – Requirements and
Certification. FEMA has granted
exceptions to a small number of
communities to allow engineered,
dry-oodproofed basements in
specic circumstances.
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NFIP TECHNICAL BULLETIN 1 MARCH 2020
A compliant enclosed area below the BFE can be
rendered non-compliant by installing features
that are inconsistent with the limitations on uses.
Examples of features that are not allowed below
the BFE are:
• Appliances
• Heating and air conditioning equipment
• Ventilation
• Ductwork
• Plumbing fixtures
• Materials that are not flood damage-resistant
materials
• More than the minimum electric service required to address life-safety and electric code requirements
for vehicle parking, building access, or storage
7 Foundation Walls and Enclosure Walls
that Require Flood Openings
The NFIP regulations require that enclosed areas below the lowest floors of elevated buildings in
Zone A have flood openings to equalize the hydrostatic flood forces (loads) on the enclosure walls. This
requirement applies whether the walls are crawlspace, load-bearing, or non-load-bearing walls.
Examples of foundation and enclosure walls that require openings are listed below and described in
Sections 7.1 through 7.9.
• Solid perimeter foundation walls (crawlspaces and under-floor spaces)
• Solid perimeter foundation walls (below-grade crawlspaces)
• Garages attached to elevated buildings
• Enclosed areas under buildings elevated on open foundations
• Enclosed areas with breakaway walls under buildings elevated on open foundations
• Above-grade (elevated) enclosed areas
• Two-level enclosed areas
• Solid perimeter foundation walls on which manufactured homes are installed
• Accessory structures (detached garages and storage sheds)
NON-CONVERSION AGREEMENTS
When some communities issue permits for
buildings with enclosed areas below the BFE,
permittees are required to execute Non-
Conversion Agreements. These agreements
document the permittees’ understanding that
the allowed use of enclosures is limited, that
conversion to other uses is not allowed, and that
modifying enclosed areas may render a building
non-compliant with minimum requirements and
result in higher NFIP ood insurance rates.
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7.1 Solid Perimeter Foundation Walls (Crawlspaces
and Under-Floor Spaces)
The crawlspace or under-floor space that is created when
a building is elevated on a solid perimeter foundation
wall that is below the BFE (see Figure 2) must meet all
of the requirements for enclosed areas, including flood
openings. If brick veneer, siding, or other material covers
the wall, the openings in the wall must penetrate into the
enclosed area. A crawlspace access door does not qualify as
a flood opening unless the door has an opening installed
in it or otherwise meets the performance requirement to
allow automatic entry and exit of floodwater.
Section 8.2 of this Technical Bulletin explains that the
bottom of each opening must be no higher than 1 foot above the higher of the finished interior grade (or
floor) or the finished exterior grade immediately under the opening. Therefore, the expected finished
exterior grade and the final interior grade (or floor) of a crawlspace must be known before the location
of the openings in a perimeter foundation wall can be determined.
Building codes may require ventilation of under-floor spaces. Ventilation openings are typically positioned
near the top of the foundation wall to facilitate air flow. In most cases, ventilation openings are too far
above grade to satisfy flood opening requirements.
In SFHAs where BFEs are several feet above grade or when owners want enough head room in an under-
floor space to allow for parking of vehicles and storage, solid perimeter foundation walls may be used to
create a full-height, under-floor space (see Figure 3). The walls surrounding an under-floor space must
meet all flood-opening requirements.
CONDITIONED CRAWLSPACES
MUST HAVE FLOOD OPENINGS
In many parts of the country, a common
practice is to build “conditioned
crawlspaces” that are sealed and have
mechanical ventilation. In SFHAs, all
crawlspaces must have ood openings
that meet the NFIP requirements and
building codes.
Figure 3: Full-height, solid perimeter walls surrounding a garage and
storage area with flood openings (only three openings are shown)
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Full-height, under-floor spaces must also meet all other NFIP requirements, which will minimize the
likelihood of future conversion to uses other than the allowed uses (parking of vehicles, building access,
or storage). Features that are inconsistent with the allowed uses are not permitted (see Section 6).
A backfilled stem wall foundation (also called
chain wall, raised-slab-on-grade, and slab-
on-stem-wall-with-fill) can look like a solid
perimeter foundation wall from the outside, but
a backfilled stem wall foundation is backfilled
with compacted structural fill, concrete, or
gravel that supports the floor slab (see Figure 4).
Because stem wall foundations are backfilled,
flood openings are not required and should not
be installed.
BACKFILLED STEM WALLS
AND NFIP ELEVATION CERTIFICATES
When the NFIP Elevation Certicate for a building
elevated on a backlled stem wall is completed,
the foundation should be described in the
comment section to clarify that the foundation is
not a crawlspace and therefore does not require
and should not have ood openings.
Figure 4: Backfilled stem wall foundation; flood openings
not required
7.2 Solid Perimeter Foundation Walls (Below-Grade Crawlspaces)
The NFIP regulations do not allow buildings in
SFHAs to have basements (areas below grade on
all sides) except for engineered, non-residential
buildings in Zone A that are designed and
certified to be dry floodproofed. Therefore,
crawlspaces that are below grade on all sides
are not allowed because they are basements. An
exception is available only in SFHAs with shallow
flooding and then only if specific requirements
and limitations are met. For more information,
LIMITATIONS ON
BELOW-GRADE CRAWLSPACES
Before authorizing below-grade crawlspaces,
communities are required to adopt specic
provisions in their ordinances to be consistent
with the limitations specied in NFIP Technical
Bulletin 11. Communities should consult NFIP
State Coordinators or FEMA Regional Ofces for
the appropriate language.
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see NFIP Technical Bulletin 11, Crawlspace Construction for Buildings Located in Special Flood Hazard Areas:
National Flood Insurance Program Interim Guidance.
According to Technical Bulletin 11, below-grade
crawlspaces may be allowed if the foundation wall
height is less than 4 feet from the bottom of the
floor joist/truss to the top of the footing or interior
grade/floor (whichever is higher). The top of the
footing or interior grade/floor must be no more than
2 feet below grade (see Figure 5). Flood openings
are required in the foundation walls surrounding
below-grade crawlspaces and, as noted in Section 7.1,
ventilation may be required. Because below-grade
crawlspaces may contribute to increased humidity
and mold growth, Technical Bulletin 11 requires that
below-grade crawlspaces have adequate drainage
systems to minimize moisture damage.
Although crawlspaces that meet the limitations in
Technical Bulletin 11 are not considered basements
for floodplain management purposes, they are
considered basements for NFIP flood insurance
purposes, and premiums will be higher if the grade
inside a crawlspace is below the exterior grade on
all sides.
7.3 Garages Attached to Elevated Buildings
Many buildings, especially homes, have an attached garage that extends laterally from the building and
may or may not have living space above it. The floor of a garage that is attached to a building in an SFHA
is allowed to be below the BFE if the garage meets all of the requirements for an enclosed area below the
BFE. The use of the garage space must be limited to parking of vehicles, building access, or storage.
Flood openings are required in the exterior walls of garages in Zone A. Openings may be installed
in garage doors (see Figure 6). However, because garage doors are likely to be replaced over the life
of a building and subsequent owners may inadvertently replace garage doors without openings, flood
openings should be installed in garage doors only when there is insufficient wall area in which to install
the required number of openings.
Garage doors themselves do not meet the requirements for openings because human intervention would
be needed to open garage doors when flooding is expected. Human intervention is inconsistent with
the requirement that openings allow for the automatic entry and exit of floodwater. Garage doors with
mechanisms that open the doors when water is detected do not meet the requirements because electric
service cannot be guaranteed even if a backup power source is provided. Similarly, gaps that may be
present between the garage door and the door jamb or walls do not guarantee automatic entry and exit of
floodwater and do not count toward the net open area requirement.
Figure 5: Limitations on below-grade crawlspaces in
shallow flood hazard areas (see NFIP Technical Bulletin 11
for more information)
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7.4 Enclosed Areas Under Buildings Elevated on Open Foundations
A building that is elevated on an open foundation (e.g., piers, posts, columns, pilings) in Zone A may have
enclosed areas below the elevated floor (see Figure 7). Sometimes, only part of the footprint is enclosed,
such as for a stairwell or storage room. All of the requirements for enclosed areas apply. Requirements
include openings, elevated utilities, flood damage-resistant materials, and limitations on use (parking of
vehicles, building access, or storage).
Skirting used to enclose areas under
manufactured homes or other elevated
buildings is typically made of weather-resistant
material and extends from the bottom of the
floor system down to grade. Rigid vinyl and
aluminum skirting must have flood openings.
Flood openings are not required when flexible
skirting is used, but flexible skirting may be
pushed against foundations if floodwater
rises rapidly, in which case open lattice may
be more appropriate. Unattached skirting
can become dislodged during flooding and
generate damaging debris.
Figure 6: Engineered openings in garage doors
NATIONAL FIRE PROTECTION ASSOCIATION
(NFPA) INSTALLATION STANDARD
AND SKIRTING
NFPA 225, Model Manufactured Home Installation
Standard (NFPA, 2017), species that the installation
of skirting does not trigger the requirement for ood
openings if the skirting does not provide structural
support and would collapse under wind and water
loads that are less than those expected during the
base ood event without causing structural damage
to the elevated home or foundation.
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7.5 Enclosed Areas with Breakaway Walls Under Buildings Elevated
on Open Foundations
Open foundations (e.g., piers, posts, columns, pilings) are recommended in riverine SFHAs where flow
velocities are expected to exceed 10 feet per second and in coastal areas where breaking wave heights
during base flood conditions are expected to be between 1.5 and 3 feet (called Coastal A Zones).
Buildings in these areas may be exposed to significant hydrodynamic loads, debris impact, and scour,
any of which could be sufficient to damage typical perimeter foundation walls and enclosure walls even
when there are flood openings.
UTILITY CHASES
For oodplain management and NFIP ood insurance purposes, utility chases designed to protect utility
lines from freezing are not considered enclosures. Utility chases must be small and not allow access for a
person to enter the space (access panels for servicing the lines are appropriate).
Because a utility chase is not considered an enclosure, it does not have to have ood openings (but ood
openings may be provided). The utility chase must be constructed of ood damage-resistant materials
below the BFE, and the enclosed utility lines must meet the requirement to be watertight and capable of
withstanding ood loads (hydrostatic, hydrodynamic, wave).
Figure 7: Enclosure with flood openings under a house elevated on pilings
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Many Flood Insurance Rate Maps (FIRMs) for
coastal communities that have been revised since
2009 show a Limit of Moderate Wave Action
(LiMWA), which delineates the inland extent of
the 1.5-foot wave. In Coastal A Zones, identified
as Zone A on FIRMs, FEMA recommends that
walls surrounding enclosed areas be designed
as breakaway walls. To comply with the NFIP
requirements, flood openings are required in
breakaway walls in Zone A.
The NFIP regulations require that enclosures
below elevated buildings in SFHAs identified as
Zone V meet the same requirements for enclosures
in Zone A, except that (1) walls must be non-
supporting breakaway walls, open lattice-work, or
insect screening and (2) flood openings are not
required (see NFIP Technical Bulletin 9, Design
and Construction Guidance for Breakaway Walls). The
guidance in Technical Bulletin 9 should be used when flood openings are installed in breakaway walls to
minimize wall failure under flooding that occurs more frequently than the base flood.
7.6 Above-Grade (Elevated) Enclosed Areas
In flood hazard areas that experience frequent
flooding, some owners construct enclosures with
floor systems that are elevated above grade, not in
contact with the ground, but still below the BFE
(see Figure 8). Placing the enclosure floor above
grade minimizes the potential for damage to the
enclosure and contents during frequent, low-level
flood events.
Above-grade enclosures must meet all requirements
applicable to enclosures (flood openings, flood damage-resistant materials, and used only for storage or
building access). The floor system of above-grade enclosures may be independently supported on piers or
posts, or enclosures may be structurally attached to the building’s column or piling foundation. Although
the floors of above-grade enclosures are not the lowest floor for floodplain management purposes, the
enclosure floors are the lowest floor for NFIP flood insurance rating purposes.
One or more floor grates should be installed in the enclosure floor to reduce the potential for structural
damage. Damage could result from buoyancy loads on the enclosure floors before water enters through
the flood openings installed in walls. Openings in floors also allow enclosures to drain completely,
reducing the potential for damage caused by the added weight of water.
I-CODES AND COASTAL A ZONE
Starting with the 2015 editions, I-Codes treat
Coastal A Zones like Zone V if the LiMWA
is delineated on FIRMs or if communities
designate Coastal A Zones. In addition,
the I-Codes and ASCE 24-14 require ood
openings in all breakaway walls, including
those in Coastal A Zones and Zone V.
Post-ood assessments indicate that
breakaway walls with openings prevent wall
failure under frequent, shallow ood events.
Preventing frequent wall failures reduces
debris, keeps enclosure interiors and contents
protected from wind-driven rain and sand,
and reduces the cost of replacing walls.
“HANGING ENCLOSURE”
The term “hanging enclosure” has been used
to refer to raised, above-grade enclosures
although above-grade enclosures are typically
supported by other means and do not actually
hang from elevated buildings.
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7.7 Two-Level Enclosed Areas
In flood hazard areas where the BFE is more than one story
above the ground, some owners want to build two-level
enclosures (see Figure 9). For compliance purposes, to avoid
the second-level enclosure from being identified as the lowest
floor, both enclosure levels must meet all of the requirements
for enclosed areas, including openings, elevated utilities, flood
damage-resistant materials, and limitations on use (parking
of vehicles, building access, or storage). To facilitate drainage
from the upper level of the enclosure, an opening with a grate
should be installed in the floor.
ABOVE-GRADE ENCLOSURES AND NFIP FLOOD INSURANCE
NFIP ood insurance policies for elevated buildings with above-grade enclosures are rated assuming
the above-grade enclosure is the lowest oor (i.e., the oor of the enclosure instead of the oor of the
elevated building). See the “Lowest Floor Guide” section of the NFIP Flood Insurance Manual (FEMA,
2019). Above-grade enclosures can result in higher NFIP ood insurance premiums than enclosures
with oors that are at-grade or close to grade. Owners should ask their insurance companies to submit
requests to the NFIP for a special rating for buildings with above-grade enclosures.
Figure 8: Above-grade enclosures
TERMS USED
FOR TWO-LEVEL ENCLOSURES
Two-level enclosures are also
referred to as two-story enclosures,
double enclosures, and stacked
enclosures.
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Figure 9 shows a two-level enclosure in which
the surrounding walls are not load-bearing; the
same configuration and requirement apply if the
surrounding walls are load-bearing perimeter walls.
Two-level enclosures are unusual and warrant
consideration of flood loads based on site-specific
flood conditions. Local officials may require that
buildings with two-level enclosures be designed
and certified by a registered design professional
rather than rely on non-engineered foundations and
enclosure configurations.
Figure 9: Two-level enclosure with non-load-bearing
walls under building elevated on pilings or columns;
configuration also applies if walls are load-bearing
TWO-LEVEL ENCLOSURES
AND NFIP FLOOD INSURANCE
Designers and owners should be aware that a
building with a two-level enclosure, even if allowed
by permit, will have a higher NFIP ood insurance
premium than if the building has a one-level
enclosure. Even if a two-level enclosure complies
with building codes and oodplain management
requirements for enclosures, the upper oor of
the two-level enclosure will be deemed the lowest
oor for insurance rating purposes (the lowest
oor for ood insurance purposes is the rst
oor elevated above ground). Owners should ask
their insurance companies to submit requests
to the NFIP for a special rating for buildings with
two-level enclosures.
7.8 Solid Perimeter Foundation Walls on which Manufactured Homes
Are Installed
Manufactured homes may be installed on solid perimeter foundation walls that enclose the space below the homes
(see Figure 10). Even if not part of a home’s load-bearing support system, a solid perimeter foundation wall is
required to have openings; otherwise, hydrostatic loads may damage the wall, which could lead to damage of the
home’s supporting foundation and anchor system.
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7.9 Accessory Structures
Communities participating in the NFIP are required to regulate all development in SFHAs, including
detached garages, detached storage buildings, and small storage sheds. Accessory structures may be
elevated in accordance with the requirements for elevated buildings or dry floodproofed.
When communities have FEMA-approved
limitations on the size of accessory structures
or when communities grant variances for non-
elevated accessory structures, the structures
may be allowed without elevation provided
the structures are wet floodproofed (see
NFIP Technical Bulletin 7, Wet Floodproofing
Requirements for Certain Buildings Located in Special
Flood Hazard Areas). Alternatively, communities
without FEMA-approved size limits may consider
granting variances for non-elevated accessory
structures in accordance with FEMA policies
and guidance.
ADDITIONAL ACCESSORY
STRUCTURE CONSIDERATIONS
Some communities have FEMA-approved
regulations that specify limitations on the size
of accessory structures that are allowed in
SFHAs without having to comply with elevation
requirements. Other considerations for accessory
structures are set forth in FEMA policies
and guidance.
Local ofcials should consult NFIP State
Coordinators or FEMA Regional Ofces for
additional guidance and for appropriate size limits
and language to include in local regulations.
Figure 10: Manufactured home supported on interior piers
and masonry perimeter wall with flood openings (ground
anchors not shown)
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Wet-floodproofed accessory structures must comply with the following measures:
• Use is limited to parking of vehicles and storage
• Utilities are elevated
• Materials below the BFE are flood damage-resistant materials
• Flood opening requirements are satisfied
• Structures are anchored to resist flotation, collapse, or lateral movement under flood conditions
A best practice is to require Non-Conversion Agreements when non-elevated accessory structures
are allowed. These agreements, when recorded with property deeds, inform future owners about
the limitations and the wet-floodproofing measures. Accessory structures that are allowed to be wet
floodproofed must not be used for any habitable or other prohibited purpose.
8 Requirements and Guidance
for Installation of Flood Openings
The NFIP regulations specify installation requirements for all flood openings, whether non-engineered
or engineered. See Section 9 of this Technical Bulletin for information on non-engineered and
engineered flood openings. Installation requirements specify the minimum number of openings and the
maximum height of openings above grade. The requirements and guidance on installation are provided
in Sections 8.1 through 8.3.
8.1 Location and Minimum Number of Flood Openings
Every enclosed area is required to have at least two
flood openings on exterior walls. Flood openings
should be installed in at least two sides of each
enclosed area to decrease the chance that all
openings will be blocked by floating debris and to
allow for more even filling and drainage of enclosed
areas than if openings are installed on only one side.
FEMA recommends that openings be distributed
around the perimeter of enclosed areas unless
there is clear justification for putting all of the openings on only one or two sides, such as in townhouses
with limited exterior walls (see Section 8.3.4) and buildings set into sloping sites (see Section 8.3.2). If
openings are not distributed around the perimeter, an imbalance in flood loads could result in damage
to or collapse of walls.
Figure 11 shows a foundation plan with multiple enclosures and openings in the perimeter wall of each
enclosed area. Note that the number of openings shown is for illustration purposes only; the total number
of openings and the adequacy of the net open area of the openings depend on the type of opening and
whether air-vent devices or engineered openings are installed.
LOCATION OF FLOOD OPENINGS
The IRC and IBC (by reference to ASCE 24)
require ood openings “on different sides of
each enclosed area” (IRC R322.2.2.1) and
“in at least two walls of each enclosed area”
(ASCE 24, Section 2.7.3).
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In some situations, openings in interior walls or partitions are necessary to ensure that floodwater can
reach all enclosed areas and minimize unbalanced hydrostatic loads on interior and exterior walls. When
openings are used in interior walls, the total number of openings and their net open area should be
based on the size of the enclosed area, but openings in interior walls are not counted toward the required
total opening requirement based on the exterior measurement of the enclosed area. To maintain safe fire
separation, flood openings should not be placed in the wall separating a garage from living spaces and
crawlspaces unless devices used as flood openings that are designed to satisfy fire-separation requirements
are used.
8.2 Height of Flood Openings Above Grade or Floor
The bottom of each flood opening must be positioned no higher than 1 foot above the higher of the final
(finished) interior or exterior grade or the floor that is immediately under each opening so water will
begin to flow through the opening when water rises just above the bottom of the opening. The purpose
of this requirement is to satisfy the performance
expectation that the difference in water levels
between the interior and exterior will not
exceed 1 foot as floodwater begins to rise and as
it recedes from the site. To reduce the amount
of water trapped inside, a good practice is to
install some openings closer to grade than the
maximum 1 foot allowed. See Section 8.3.6 for
information on openings that extend above the
BFE in areas with shallow flooding.
When interior and exterior grades are different,
the higher of (1) the finished exterior grade
immediately under each opening and (2) the
final interior grade or floor is used to determine
Figure 11: Foundation plan of home with multiple enclosed areas, each with flood
openings (number of openings for illustration purposes only)
ENCLOSURES BELOW GRADE
ON ALL SIDES ARE BASEMENTS
An enclosure that is below grade on all sides is
a basement regardless of whether the interior
grade or oor is below grade because backll,
topsoil, or landscaping materials were added or
because the footing trenches inside the perimeter
foundation walls are not completely backlled.
Basements do not comply with the minimum
NFIP requirements. In addition, the presence of
such below-grade enclosures will result in higher
NFIP ood insurance premiums.
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the position of flood openings. The following should be considered when determining which grade or
floor to use:
• Finished exterior grade. Care should be taken when placing backfill, topsoil, or landscaping materials
around the outside of enclosures, especially solid perimeter foundation walls. If the finished exterior
grade is higher than the interior grade on all sides of the building, the enclosed area will be a
basement as defined by the NFIP.
• Final interior grade or floor. The trench that is excavated to construct footings and foundation walls
must be backfilled completely; otherwise, a basement will be created. If the interior grade or floor is
higher than the exterior grade, the openings must be no higher than 1 foot above the interior grade
or floor.
8.3 Examples of Flood Opening Installations
The following examples of flood opening installations are described in Sections 8.3.1 through 8.3.6:
• Interior grade or floor higher than the exterior grade
• Sloping sites
• Buildings with large enclosed areas
• Townhouses with limited exterior walls
• Buildings with multiple enclosures
• Openings in areas with shallow flooding
8.3.1 Interior Grade or Floor Higher than the Exterior Grade
This section describes enclosures in which
the interior grade or floor is higher than
the exterior grade. As water rises against
the outside of the foundation, the interior
fill or slab resists the hydrostatic load. When
water rises above the interior grade or slab,
the lateral load will become unbalanced
and therefore must be equalized with
openings that allow water to automatically
enter and exit.
Figure 12 is an example of a framed
enclosure below a manufactured home
that is elevated on columns. As indicated
by the driveway on the left, the interior slab
is higher than the exterior grade along the
side of the building. The flood openings are
within 1 foot of the interior floor surface.
Here, the full-height enclosed area is used
for parking of vehicles and storage.
Figure 12: Manufactured home installed on columns above a full-
height, framed garage (note elevation of thick driveway slab on left;
the flood openings are within 1 foot of interior floor surface)
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When viewed from the outside, an enclosure with
the interior grade or floor higher than the exterior
grade may appear non-compliant with the installation
requirements for openings because the openings
appear to be too high above the exterior grade.
Therefore, the final documentation of as-built
elevations should note the difference in interior and
exterior grades. For example, if the NFIP Elevation
Certificate is used, the comments should indicate
whether the openings are (or are not) within 1 foot of
the higher of the two grades and should explain that
the interior grade or floor is higher than the exterior
grade. Without the explanation, NFIP flood insurance
premiums may be higher than necessary.
8.3.2 Sloping Sites
Buildings on solid perimeter foundation walls set into sloping sites present a special situation for the
installation of flood openings. Careful attention must be paid to the following:
• The interior grade or floor along the lowest side of the building must be at or above the exterior grade
across the entire length of the lowest side, and there must be positive surface drainage away from the
building; otherwise, the enclosure will be considered a basement as defined by the NFIP.
• The bottom of each opening must be no higher than 1 foot above the exterior or interior grade
immediately below the opening, whichever is higher (see Figure 13).
• For flood openings to perform their intended function, they should be below the BFE.
INTERIOR GRADE
OR FLOOR ABOVE BFE
When the interior grade or oor of an
enclosure below an elevated building is
entirely above the BFE, ood openings are
recommended but not required. When the
oor of an enclosure is above the BFE, the
NFIP ood insurance policy will be rated
using the enclosure oor as the lowest oor
rather than the next higher oor above the
enclosure. Installing ood openings in these
situations will result in lower NFIP ood
insurance premiums.
Figure 13: Flood openings in enclosure walls on a sloping site
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• Interior partitions and load-bearing walls must have openings to allow water to readily reach every
enclosed area (see Section 8.3.5 for information on buildings with multiple enclosures).
8.3.3 Buildings with Large Enclosed Areas
Some buildings, especially commercial and industrial buildings, have large under-floor spaces,
crawlspaces, or enclosures. Flood openings may be stacked or grouped (see Figure 14), or large-dimension
openings may be used, provided all of the requirements for openings are satisfied. Vertically stacked or
closely spaced openings function together as one opening, and the bottom of the lowest opening must be
no higher than 1 foot above the exterior grade or interior grade, whichever is higher.
Figure 14: Flood openings that are stacked and closely grouped to
satisfy the required total net open area
8.3.4 Townhouses with Limited Exterior Walls
Townhouses are single-family dwelling units constructed in groups of three or more attached units in
which each unit extends from foundation to roof with exterior walls on at least two sides. Flood openings
are required for townhouses in SFHAs that are constructed with solid perimeter foundation walls or solid
walls surrounding enclosed areas under the elevated portion of the building.
Because interior townhouse units have less linear exterior wall length than end units, meeting all of the
requirements for flood openings can be a challenge, especially the requirement for adequate opening
area and the requirement that each enclosed area have openings. If openings cannot be provided in at
least two exterior walls of each enclosed area, the NFIP allows all openings to be installed in one wall.
NFIP TECHNICAL BULLETIN 1 MARCH 2020
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The design of interior townhouse units can satisfy the guidance that openings should be located on
different sides of each enclosed area if interior partitions and walls have openings to connect enclosed
spaces from front to back. Figure 15 shows suggested locations for openings. Note that the number of
openings in Figure 15 is for illustration purposes only; the total number of openings and the adequacy of
the opening area depend on the type of opening and whether non-engineered or engineered openings are
installed. Fire-safety limitations generally preclude openings in the walls that separate townhouse units.
Providing adequate openings in enclosures below elevated townhouse units, other than end units, may be
even more challenging if a multi-unit building is set into a sloping site. In this case, it may be appropriate
to consider an open foundation or a backfilled stem wall foundation that does not require openings.
Figure 15: Suggested flood openings in enclosures under elevated townhouses (number of openings for illustration
purposes only)
8.3.5 Buildings with Multiple Enclosures
Every enclosed area is required to meet the requirements for enclosures, including the requirement for
flood openings in exterior walls. Figure 11 in Section 8.1 shows a home foundation plan with multiple
enclosures. In some situations, openings in interior walls or partitions may be necessary to ensure that
floodwater can reach all areas to minimize unbalanced hydrostatic loads on load-bearing interior walls
and exterior walls (see middle townhouse in Figure 15 in Section 8.3.4). When openings are used in
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NFIP TECHNICAL BULLETIN 1 MARCH 2020
interior walls, the total number of openings in exterior walls and the total opening area should be based
on the size of the entire enclosed area. Openings in interior walls do not count toward the total opening
requirements based on the exterior measurement of the enclosed area.
8.3.6 Flood Openings in Areas with Shallow Flooding
Some FIRMs show mapped SFHAs where the depth
of floodwater above grade will be shallow (2 feet or
less during the base flood). Shallow flooding occurs
toward the landward boundary of SFHAs and in areas
identified as being subject to sheet flow or ponding.
The NFIP regulations require flood openings in
enclosures even if the depth of flooding is only 1 foot
and the difference in water depth between the inside
and outside of enclosures is 1 foot or less.
Depending on the depth of floodwater in areas with
shallow flooding, flood openings may extend above
the BFE if the bottom of the opening is no higher than 1 foot above the higher of the final interior grade
or floor and the finished exterior grade of the crawlspace or enclosure. When flood openings extend
above the BFE, alternatives to satisfy the requirements include:
• Raise the floor of the enclosure to be at or above the BFE, perhaps by using a thicker slab, resulting in
no need for openings. Although this alternative satisfies the construction requirement, for NFIP flood
insurance rating purposes, the top of the slab is the elevation of the lowest floor, not the next higher
floor (see the text box “Interior Grade or Floor above BFE” in Section 8.3.1).
• Install openings as close to grade (or floor) as possible to maximize the open area available for inflow
and outflow of floodwater (see Figure 16). The total net open area of the openings must be based on
the enclosed area even if some portion of the opening is above the BFE.
Figure 16: Bottom of the flood opening positioned as close as
possible to grade (or floor) when any portion of the opening extends
above the BFE
NFIP ELEVATION CERTIFICATE
AND SHALLOW FLOODING
The NFIP Elevation Certicate requires
users to input the number of ood openings
within 1.0 foot above the adjacent grade or
oor. The certicate does not require users
to determine how much of a ood opening
is above or below the BFE.
NFIP TECHNICAL BULLETIN 1 MARCH 2020
27
9 Non-Engineered Flood Openings
and Engineered Flood Openings
The NFIP regulations, described in previous sections, identify
options for providing sufficient size and number of flood
openings to allow for the automatic (free) entry and exit of
floodwater. This section describes how the automatic entry
and exit of floodwater can be accomplished by the use of:
• Non-engineered openings that meet the prescriptive
requirement to provide 1 square inch of net open area
for each square foot of enclosed area, where the enclosed
area is measured on the exterior of the enclosure walls.
Section 9.2 describes a variety of options that can serve as
non-engineered openings.
• Engineered openings for which Evaluation Reports are
issued by the ICC Evaluation Service (ICC-ES), a subsidiary
of the ICC, or equivalent reports issued by other product
certification organizations.
• Engineered openings designed and certified by a
registered design professional for a specific building and
site-specific conditions.
All of the following requirements for installation apply
regardless of whether engineered openings or non-engineered
openings are used to satisfy the NFIP requirements (also see
Section 8):
• Each enclosed area must have a minimum of two openings.
When multiple enclosed areas are present, each area must have openings in its exterior walls.
Section 8.3.5 describes connecting multiple areas by installing openings in interior walls or partitions
to ensure that floodwater can reach all enclosed areas.
• The bottom of each opening must be no more than 1 foot above the higher of the final interior grade
or floor or the finished exterior grade immediately under the opening.
• Insect screens, grates, grilles, fixed louvers, blades, faceplates, or other devices, if any, must not block
the automatic flow of floodwater into and out of the enclosed area.
Section 9.1 provides a list of measures that are not acceptable as flood openings.
I-CODE REQUIREMENTS
FOR FLOOD OPENINGS
The IRC includes requirements for
non-engineered and engineered
ood openings, and the IBC
includes the same requirements by
reference to ASCE 24.
FLOOD DAMAGE-RESISTANT
MATERIALS
Flood openings must be made of
ood damage-resistant materials
in order to satisfy the requirement
that materials used below the
BFE be resistant to ood damage.
Metals should be corrosion
resistant, and plastics should be
weather resistant. For guidance,
see NFIP Technical Bulletin 2,
Flood Damage-Resistant
Materials Requirements.
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NFIP TECHNICAL BULLETIN 1 MARCH 2020
9.1 Measures Not Acceptable as Flood Openings
FEMA has determined that the following measures do not satisfy the requirements for flood openings:
• Standard foundation air-ventilation devices that can be closed manually unless they are permanently
disabled in the open position because otherwise, they do not allow for the automatic entry and exit of
floodwater (see Figure 17).
• Standard foundation air-ventilation devices that have detachable solid covers intended to be manually
installed over the vent because they do not allow for the automatic entry and exit of floodwater when
the cover is in place.
• Standard foundation air-ventilation devices that are designed to open and close based on temperature
unless they are also designed to allow for the automatic entry and exit of floodwater.
• Devices with covers or panels that are intended to displace when floodwaters rise on only one side
of a wall because they do not satisfy the requirement for automatic entry and exit of floodwater in
both directions.
• Windows below the BFE because the automatic entry and exit of floodwater cannot be satisfied by the
expectation that windows will break under rising floodwater.
• Garage doors without openings because human intervention is required to open garage doors when
flooding is expected. Gaps between the garage door and the door jamb or walls do not count toward
the net open area requirement.
9.2 Non-Engineered Flood Openings
Flood openings without moving parts are non-engineered openings, while those with moving parts
should be certified as engineered openings (see Section 9.3). Non-engineered openings are used to
provide 1 square inch of net open area for each square foot of enclosed area. The size of an enclosed
Figure 17: Standard air vent that is unacceptable as a flood opening
because it is not disabled in the open position
NFIP TECHNICAL BULLETIN 1 MARCH 2020
29
area in square feet should be measured
on the exterior of the enclosure walls. A
variety of non-engineered opening options
are available.
“Net open area” refers to the permanently
open area of a non-engineered opening.
The NFIP regulations indicate that flood
openings may be equipped with “coverings
or devices” if they permit the automatic
(free) entry and exit of floodwater in
both directions.
The measurement of the net open area must
take into consideration any solid obstructions
such as grilles, fixed blades and louvers, or
faceplates. Methods used by the ventilation
industry to account for such obstructions
when determining net open area for air
flow may be used. Figure 18 shows a typical
standard air-vent faceplate and measurements
of the net open area. Figure 19 shows a typical
ventilation louver with fixed blades and
indicates how the net open area is determined.
Some manufacturers of standard air vents
stamp the number of square inches the
device provides for air flow into the frame
of the device or may note the number in the
packaging. The measurement accounts for
MEASUREMENT MUST ACCOUNT
FOR OBSTRUCTIONS
Section C2.7.2.1 of the ASCE 24 commentary
emphasizes that the measurement of net open area
is not based on the dimensions of the opening (void)
in the wall. The measurement must account for any
portion of the void that is obstructed or covered in
any way (other than by screening).
Figure 18: Example
of non-engineered opening: Typical standard
air vent faceplate providing 42 square inches of net open area if
disabled in the open position; measurement of net open area uses a
slot width of 0.5 inch times a slot height of 6.5 inch times the total
number of slots
Figure 19: Example of non-engineered opening: Typical standard air vent with fixed, angled
blades providing approximately 44 square inches of net open area; measurement of net
open area uses slot width of 13 inches times the sum of the spaces between the blades
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NFIP TECHNICAL BULLETIN 1 MARCH 2020
the presence of fixed blades, insect screens, and other obstructions. The same number of square inches
should be used for the net open area calculation when these devices are installed as non-engineered
openings. If not indicated by the manufacturer, the net open area must be measured. Guidance on
measuring the net opening area may be available from manufacturers or other sources.
To qualify as non-engineered flood openings that permit the automatic entry and exit of floodwater:
• Standard air vents must not have solid covers (detachable or integrated with the vent) that are
intended to be manually installed.
• Typical air-vent devices that are designed to be opened and closed manually must be disabled
permanently in the open position.
• Air-vent devices that are designed to open and close based on temperature must also be designed to
allow the automatic entry and exit of floodwater.
Insect screens that do not block the entry and exit
of floodwater are allowed and do not affect the
determination of the net open area. Communities
that administer the IBC or IRC should note the
requirement to cover ventilation openings for
crawlspaces and under-floor spaces. The codes
provide a list of acceptable covering materials.
The IBC and IRC commentaries note that some
covering materials for ventilation openings may
reduce the gross open area of the vent by as much
as 50 percent. Although the net open area is not
reduced by screens, in areas where floodwater is
expected to carry debris such as grass clippings and
leaves, insect screens tend to clog (see Figure 20).
Engineers, architects, and local officials may determine that a different type of opening is appropriate
or that more than the minimum number of flood openings is required to increase the likelihood that
openings will perform as expected during flooding, even if some of them become clogged with debris.
AREAS LIKELY TO HAVE
DEBRIS AND SEDIMENT
Section C2.7.2.1 of the ASCE 24 commentary
suggests using caution in selecting or
specifying openings with louvers, blades,
screens, or faceplates that may be blocked
by debris and sediment. In areas where
experience indicates that oodborne
debris and sediment are likely, ASCE 24
recommends avoiding the use of openings
with components that have been shown to
become blocked or clogged.
Figure 20: Typical air vents with insect screens blocked by flood debris
NFIP TECHNICAL BULLETIN 1 MARCH 2020
31
Examples of non-engineered openings are described
below and shown in Figures 21 through 24.
• Figure 21 shows typical standard air-ventilation
devices that are intended for crawlspace foundation
walls. If installed as flood openings, they must
be disabled permanently in the open position to
satisfy the requirement for automatic entry and exit
of floodwater.
• Figure 22 shows decorative masonry units and
decorative brickwork with closely spaced, open
holes. Only the net open area of each hole is counted.
• Figure 23 shows standard concrete blocks that are turned sideways and have insect screening. The
voids in the blocks are measured to determine the net open area.
• Figure 24 shows a foundation in which a hole was created when the concrete was poured. The
horizontal dimension should be greater than the vertical dimension to facilitate flow-through. A
wood frame covered with insect screening is inserted into the hole. The framed void is measured
to determine the net open area. A similar situation results when a block is omitted from perimeter
foundation walls constructed of concrete masonry units, resulting in a void the size of the
omitted block.
MINIMUM DIMENSION
SPECIFIED BY I-CODES
The IRC and IBC (by reference to
ASCE 24) require that openings be not less
than 3 inches in any direction in the plane
of the wall. This requirement applies to the
opening in the wall, excluding any device
that may be inserted.
Figure 21: Examples of typical air vents in crawlspace foundation walls used as flood openings with varying net open areas
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NFIP TECHNICAL BULLETIN 1 MARCH 2020
Figure 23: Concrete blocks turned sideways with insect screening;
a typical 8- by 16-inch block provides approximately 60 square
inches of net open area
Figure 22: Decorative masonry units and closely spaced holes in brickwork; the area of each hole counts toward the
total net open area
NFIP TECHNICAL BULLETIN 1 MARCH 2020
33
Figure 24: Wood frame with insect screen inserted in void in poured
concrete foundation wall; inside dimensions of frame determine net
open area
9.3 Engineered Flood Openings
Engineered flood openings, which have moving parts, must be designed and certified by registered design
professionals as engineered flood openings (see Section 9.2 for openings without moving parts). The
certification must specifically address the performance required by the NFIP regulations. Devices with
moving parts should be certified as engineered openings. In general, engineered openings remain closed
until flood conditions trigger the movable parts to allow floodwater and debris to freely and automatically
enter or exit. This section describes the design and performance requirements and the certification and
documentation requirements for engineered openings.
9.3.1 Design and Performance Requirements
The design and performance criteria for engineered openings are in ASCE 24, Section 2.7.2.2.
Section C2.7.2.2 of the ASCE 24 commentary provides additional information on engineered openings
and the best means to test expected performance.
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NFIP TECHNICAL BULLETIN 1 MARCH 2020
ASCE 24 EMPHASIS ON PERFORMANCE
AND CERTIFICATION
Engineered opening requirements changed
between the 2005 and 2014 editions of ASCE 24.
The 2014 edition places more emphasis on
evidence of performance and consideration of
factors that represent expected ood conditions.
Section C2.7.2.2 of the ASCE 24-14 commentary
notes that the best means to certify performance
is to test engineered openings under conditions
that mimic a range of rates of rise and fall,
including rates many times the minimum rate of
5 feet per hour.
Documentation of performance under faster rates
of rise and fall provides building designers and
local ofcials with sufcient information on which
to base decisions regarding whether to increase
the number or size of openings to account for
faster rates. The ASCE 24 commentary also notes
that testing should be done with water containing
debris typical of ooding around buildings (e.g.,
leaves, grass clippings, small branches, trash).
Figure 25: Equation used to determined total net area of engineered openings (ASCE 24-14; used
with permission)
The equation includes a coefficient (0.033) that
corresponds to a factor of safety of 5, which is
consistent with design practices related to the
protection of life and property. The ASCE 24
commentary provides additional background on
the derivation of the equation.
Design and performance criteria for engineered
openings specified in ASCE 24 include all of
the following:
• Performance must allow for the automatic
entry and exit of floodwater. The ASCE 24
commentary notes that the certification
requires consideration of a number of
factors that represent expected base flood
conditions and not simply application of the
equation. (Flood conditions in different areas
can vary widely; in some areas, the onset of
flooding may be rapid while in other areas,
flood conditions may develop over much
longer periods.)
• Performance must account for the presence
of obstructions such as louvers, blades,
screens, grilles, faceplates, and devices that
are part of the engineered opening assembly itself. In accordance with ASCE 24, Table 2-2 (see Table
3 of this Technical Bulletin), the opening coefficient of discharge (c) is 0.20 for openings of all shapes
if partially obstructed during design flood conditions by “louvers, blades, screens, grilles, faceplates,
or other covers or devices [that] are present during the design flood,” as opposed to blocked by debris.
A
0
= 0.033 [1/c] R A
e
Where: A
0
= total net area of openings required (in
2
)
0.033 = coefficient corresponding to a factor of safety of 5.0 (in
2
⦁
hr/ft
3
)
c = opening coefficient (non-dimensional; see ASCE 24, Table 2-2)
R = worst case rate of rise and fall (ft/hr)
A
e
= total enclosed area (ft
2
)
The equation from ASCE 24, shown in Figure 25, is used to determine the total net area of engineered
openings required for a given total enclosed area, based on some of the characteristics of the openings.
The calculated minimum net area of engineered openings may be called the “coverage” or “rated” area.
NFIP TECHNICAL BULLETIN 1 MARCH 2020
35
Table 3: Flood Opening Coefficient of Discharge
(1)
Opening Shape and Condition c
All shapes, partially obstructed during design ood
(2)
0.20
Circular, unobstructed during design ood 0.60
Rectangular, long axis horizontal, short axis vertical, unobstructed during design ood 0.40
(3)
Square, unobstructed during design ood 0.35
Rectangular, short axis horizontal, long axis vertical, unobstructed during design ood 0.25
(4)
Other shapes, unobstructed during design ood 0.30
Source: ASCE 24-14, Table 2-2 (used with permission)
(1) Different coefcients of discharge shall be permitted: (1) where a designer has performed detailed, opening-specic
calculations, a coefcient of discharge up to 10% different than given in Table 2-2 shall be permitted; or (2) where
laboratory testing or numerical modeling of ow through the opening has been conducted, the resulting coefcient of
discharge shall be permitted. In no case shall a coefcient of discharge >0.60 be permitted.
(2) Openings shall be classied as partially obstructed if louvers, blades, screens, grilles, faceplates, or other covers or
devices are present during the design ood.
(3) When the horizontal dimension is twice or more the vertical dimension, use 0.4; as the dimensions approach a square,
interpolate from
0.4 to 0.35.
(4) When the horizontal dimension is half or less the vertical dimension, use 0.25; as the dimensions approach a square,
interpolate from 0.25 to 0.35.
FLOODWATER RATE OF RISE AND FALL
Section C2.7.2.2 of the ASCE 24 commentary
notes that a rate of rise of 5 feet per hour, only
1 inch per minute, is not representative of
many ood hazard areas and advises building
designers to be cautious about relying entirely
on that rate. Faster rates of rise and fall are
likely in watersheds where rainfall runoff
accumulates rapidly and in many areas that
are subject to storm surge ooding. ASCE 24
advises that information on rates of rise may
be available from stream and tide gauges;
federal, state, and local sources; and video
documentation of past ood events.
• Performance must account for the potential
for debris blockage even if there are no
louvers, blades, screens, grilles, faceplates, or
other devices, preferably by allowing typical
floodborne debris to pass through.
• Performance must ensure that the difference
between the exterior and interior water levels
will not exceed 1 foot. (Because the minimum
requirement allows the bottom of openings to
be no more than 1 foot above the higher of the
finished interior grade [or floor] or exterior
grade, a difference of no more than 1 foot is
maintained when water begins to pass through
as it crests the bottom of the opening frame.)
• The minimum dimension of an opening in
a wall must not be less than 3 inches in any
direction in the plane of the wall.
• Reliable data on the rates of rise and fall at specific locations are usually not readily available.
Therefore, engineered openings must be designed and must function based on the assumption that
the minimum rate of rise and fall will be 5 feet per hour. Reinforcing the importance of testing for
(The coefficient of discharge, also called an orifice coefficient, is selected to characterize the shape of
the portion of an engineered opening through which water flows.)
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NFIP TECHNICAL BULLETIN 1 MARCH 2020
faster rates of rise and fall, building designers must increase the specified total net area of engineered
openings when site-specific data or analyses of anticipated flood conditions indicate that more rapid
rates of rise and fall are likely.
9.3.2 Documentation of Engineered Openings for Compliance
Engineered openings should be accepted by local
officials when the designs are certified and the
certifications are submitted as part of permit
applications. Acceptable documentation of certification
are the certification reports (i.e., ICC-ES Evaluation
Reports or equivalent reports from other product
certification organizations) and individual certifications
for specific buildings (see Section 9.3.4).
Copies of the certifications must be kept in the
community’s permanent permit files. Community
retention of these documents is important not only
to demonstrate compliance but also in the event that
future building owners do not receive copies of the
certifications when they buy buildings. Owners must
submit certifications with applications for NFIP flood
insurance policies.
9.3.3 Engineered Openings with Certification Reports
The ICC-ES and other product certification organizations develop criteria for acceptance of a variety of
building products, construction methods, and materials. Each organization issues certification reports
after technical evaluation of documentation that is submitted by manufacturers. Documentation typically
includes technical design reports, certifications,
and testing results to demonstrate performance and
compliance with codes and standards. Certification
reports provide evidence that products comply with
specific building codes and standards. Designers,
builders, and local officials who rely on these reports
must determine whether the reports identify the editions
of the building codes and ASCE 24 that are applicable
to individual projects. If applicable editions of the codes
and standard are not identified, the certification report
should not be used.
Documentation submitted by manufacturers to obtain
an ICC-ES Evaluation Report or equivalent certification
report for engineered openings must be supported
by certifications describing the performance of the
openings and the name, title, address, type of license,
license number, the state in which the license was issued,
and the signature and seal of the certifying registered
I-CODES REQUIRE
DESIGN STATEMENTS
The IBC and IRC require that construction
documents submitted for building
permits include design statements by
registered design professionals when
applicants propose using engineered
openings. ICC-ES Evaluation Reports and
equivalent certication reports satisfy this
requirement.
Individual certications prepared for
specic buildings also satisfy the
requirement for design statements.
SITE-SPECIFIC APPLICABILITY
OF ENGINEERED OPENINGS
When an engineered opening product
with a certication report issued by
ICC-ES or an equivalent product
certication organization is specied in
construction documents, the engineer,
architect, or builder should determine
whether the product, given its limitations
and conditions of use, is appropriate
for the conditions of ooding at the site,
especially the rate of rise and fall of
oodwater. Designers should consult
with local ofcials regarding observations
of past rates of rise and fall during
conditions of ooding.
NFIP TECHNICAL BULLETIN 1 MARCH 2020
37
design professional. The certification reports must include a description of installation requirements or
limitations that, if not followed, would void the certification. FEMA considers the following documentation
important:
• Statement certifying that the openings, when properly installed, are designed to automatically
equalize hydrostatic flood loads on exterior walls by allowing the automatic entry and exit of
floodwater in accordance with the design and performance requirements in ASCE 24.
• Statement certifying that the performance accounts for the presence of louvers, blades, screens,
grilles, faceplates, or devices with consideration of the potential for debris blockage when these
features are present.
• Description of the measurement of the actual net area of the engineered opening that is being
certified and identification of the opening coefficient of discharge, which is the variable c in the
formula in ASCE 24 (see Figure 25 and Table 3 of this Technical Bulletin). The coefficient of
discharge is selected by the designer based on the shape and dimensions of the opening and whether
the engineered opening has features such as louvers, blades, screens, grilles, faceplates, or devices that
partially obstruct flow during conditions of flooding.
• The range of flood characteristics tested for which the certification is valid, specifically the rates of
rise and fall of floodwater, which is the variable R in the formula in ASCE 24 (see Figure 25), and
whether there are any limitations based on rates of rise and fall that are faster than 5 feet per hour.
Given the ASCE 24 performance expectations, engineered openings must function during conditions
of the minimum 5 feet per hour rate of rise and fall.
9.3.4 Engineered Openings Individually Certified for Specific Buildings
Engineered openings that do not have ICC-ES Evaluation Reports or equivalent certification reports must
be individually certified as meeting the design requirements described in Section 9.3.1 of this Technical
Bulletin and for acceptability in specific buildings based on site-specific conditions. The formula in
Section 9.3.1 includes the variable R, which is the worst-case rate of rise and fall at a specific location.
ASCE 24 allows the assumption of a minimum rate of rise and fall of 5 feet per hour only in the absence
of reliable data on site-specific rates of rise and fall. Building designers who specify engineered openings
that are individually certified should consult local officials regarding observations of past rates of rise and
fall during conditions of flooding.
Generic certifications for manufactured products
place the burden on users (who may not be design
professionals) to determine whether a specific
location is subject to rates of rise and fall greater
than 5 feet per hour. For this reason, generic “fill-in-
the-blank” certifications are not acceptable when a
manufactured product is used for a specific building
unless the builder or design professional for that
building, or the local official, determines that the
rates of rise and fall at the specific location are no
faster than 5 feet per hour. Alternatively, the builder
or design professional may submit documentation
that there are no reliable data for site-specific rates of
INDIVIDUAL CERTIFICATION
FOR SPECIFIC BUILDINGS MUST
ADDRESS SEVERAL FACTORS
Section C2.7.2.2 of the ASCE 24
commentary indicates that “certication
requires more than simply applying the
equation … it requires consideration of a
number of factors that represent expected
base ood conditions.” The commentary
also notes that engineered openings should
be tested unless uniquely designed for a
specic location.
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NFIP TECHNICAL BULLETIN 1 MARCH 2020
rise and fall, in which case the local official may concur that the rates may be assumed to be no faster
than 5 feet per hour.
When engineered openings that have been individually certified for specific buildings are used, the permit
application must include a certification that is signed and sealed by the registered design professional,
who must be licensed to practice in the state in which the building is located. In addition, the submitted
plans must identify the location for the openings and specify installation instructions.
The original certification for engineered openings prepared for specific buildings must include the
design professional’s name, title, address, signature, type of license, license number, the state in which
the license was issued, and the signature and applied seal of the certifying registered design professional.
The original certification must identify the physical location of the building in which the engineered
openings will be installed.
This Technical Bulletin relies on the ASCE 24 requirements for engineered openings as the accepted
standard of practice. The certification must include a description of installation requirements or
limitations that, if not followed, will void the certification. In addition to the design and certification
criteria listed in Section 9.3.1, the certification must include the following:
• Statement certifying that the openings, when properly installed, are designed to automatically
equalize hydrostatic flood loads on exterior walls by allowing the automatic entry and exit of
floodwater in accordance with the design and performance requirements in ASCE 24.
• Statement certifying that the performance accounts for the presence of louvers, blades, screens,
grilles, faceplates, or devices with consideration of the potential for debris blockage when these
features are present.
• Description of the measurement of the actual net area of the engineered opening and identification
of the opening coefficient of discharge, which is the variable c in the formula in ASCE 24 (see
Figure 25 and Table 3 of this Technical Bulletin). The coefficient of discharge is selected by the
designer based on the shape and dimensions of the opening and whether the engineered opening
has features such as louvers, blades, covers, screens, grilles, faceplates, or other elements that partially
obstruct flow during conditions of flooding.
• Determination of the rate of rise and fall of floodwater at the site and a statement certifying that the
openings are designed for that rate of rise and fall or a statement that the opening is designed for a
minimum rate of rise and fall of 5 feet per hour because reliable data on site-specific rates of rise and
fall are not available.
NFIP TECHNICAL BULLETIN 1 MARCH 2020
39
9.3.5 NFIP Elevation Certificate and Documentation of Engineered Openings
for Flood Insurance
When engineered openings are used, the NFIP Elevation Certificate must be completed carefully. The
question “Engineered flood openings?” must be answered with “Yes” (see A8.d and A9.d in Figure 26).
The engineered opening documentation must be attached to the NFIP Elevation Certificate. Insurers
and insurance agents must ask property owners to provide the documentation as part of applications for
NFIP flood insurance policies. The following are acceptable forms of documentation:
• For engineered openings with ICC-ES Evaluation
Reports or equivalent reports from other product
certification organizations, a copy of the report
that identifies the manufacturer’s model number
and specifies the number of such openings that
are required for a specified square footage of
enclosed area
• For engineered openings individually certified for
installation in a specific building, a certification
that is signed and sealed by a registered design
professional who is licensed in the state where the
building is located, and that addresses the statements
described in Section 9.3.4
To complete the NFIP Elevation Certificate with information required for proper rating of NFIP flood
insurance policies for buildings with engineered openings, Item A8.c, “Total net area of flood openings in
A8.b,” must be filled in with the total coverage or rated area of engineered openings. The total coverage
or rated area is the number of engineered openings identified in Item A8.b multiplied by the “coverage”
area, “rated” area, or “enclosed area coverage” identified in the ICC-ES Evaluation Report, equivalent
report, or individual certifications. When engineered openings are used in attached garages, Item A9.c
must be completed in the same manner. The coverage or rated area usually is given in square feet of
enclosed area for which an engineered opening can provide automatic inflow and outflow of floodwater,
which is, in effect, equivalent to the performance that would be provided by that number of square inches
of non-engineered openings.
Also, in Section D, “Check here if attachments” must be selected, and a copy of the certification
report must be attached to the NFIP Elevation Certificate (see Figure 26). Notes must be added in the
Section D comment section to identify the manufacturer and the manufacturer’s model number of the
engineered opening.
NFIP ELEVATION CERTIFICATES
AND NON-ENGINEERED OPENINGS
When non-engineered openings are
used, the total net open area of the
openings that are within 1.0 foot above
the higher of the exterior or interior
grade or oor should be determined by
measurement (see examples in
Section 9.2) or by using the
manufacturer’s specications.
40
NFIP TECHNICAL BULLETIN 1 MARCH 2020
Figure 26: Completing the NFIP Elevation Certificate when engineered openings are used
NFIP TECHNICAL BULLETIN 1 MARCH 2020
41
10 References
This section lists the references cited in this Technical Bulletin. Additional resources related to NFIP
requirements are provided in Technical Bulletin 0.
ASCE/SEI. 2014. ASCE/SEI 24-14, Flood Resistant Design and Construction. Available at
https://www.asce.org/.
FEMA (Federal Emergency Management Agency). Various NFIP Technical Bulletins. Current editions
are available at https://www.fema.gov/nfip-technical-bulletins:
• Technical Bulletin 0, Users Guide to Technical Bulletins.
• Technical Bulletin 2, Flood Damage-Resistant Materials Requirements.
• Technical Bulletin 3, Non-Residential Floodproofing – Requirements and Certification.
• Technical Bulletin 7, Wet Floodproofing Requirements for Certain Buildings Located in Special
Flood Hazard Areas.
• Technical Bulletin 9, Design and Construction Guidance for Breakaway Walls.
• Technical Bulletin 11, Crawlspace Construction for Buildings Located in Special Flood Hazard
Areas: National Flood Insurance Program Interim Guidance.
FEMA. 2004. FEMA 467-1, Floodplain Management Bulletin: Elevation Certificate. Available at
https://www.fema.gov/media-library/assets/documents/3539.
FEMA. 2010. FEMA P-758, Substantial Improvement/Substantial Damage Desk Reference. Available at
https://www.fema.gov/media-library/assets/documents/18562.
FEMA. 2013. FEMA P-936, Floodproofing Non-Residential Buildings. Available at http://www.fema.gov/
media-library/assets/documents/34270.
FEMA. 2015. FEMA Form 086-0-33, NFIP Elevation Certificate and Instructions. Available at http://www.
fema.gov/media-library/assets/documents/160.
FEMA. 2018. FEMA 213, Answers to Questions About Substantially Damaged Improved/Damaged Buildings.
Available at https://www.fema.gov/media-library/assets/documents/169099.
FEMA. 2019. NFIP Flood Insurance Manual. Available at https://www.fema.gov/flood-insurance-manual
ICC (International Code Council). International Codes. Available at https://codes.iccsafe.org/
category/I-Codes.
• 2012 International Building Code
• 2012 International Residential Code
• 2015 International Building Code
• 2015 International Residential Code
• 2018 International Building Code
• 2018 International Residential Code
NFPA (National Fire Protection Association). 2017. NFPA 225, Model Manufactured Home Installation
Standard. Available at www.nfpa.org.
