B08 Attach 6 Fema tb1 Openings Foundation Walls of Enclosures 031320.pdf

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

2 National Flood Insurance Program Regulations

3 Building Codes and Standards

3.1 International Residential Code

3.2 International Building Code and ASCE 24

4 NFIP Flood Insurance Implications

5 Documenting Building Elevations and Flood Openings Using the NFIP Elevation Certificate

6 Use of Enclosed Areas Below Elevated Buildings

7 Foundation Walls and Enclosure Walls that Require Flood Openings

7.1 Solid Perimeter Foundation Walls (Crawlspacesand Under-Floor Spaces)

7.2 Solid Perimeter Foundation Walls (Below-Grade Crawlspaces)

7.3 Garages Attached to Elevated Buildings

7.4 Enclosed Areas Under Buildings Elevated on Open Foundations

7.5 Enclosed Areas with Breakaway Walls Under Buildings Elevated on Open Foundations

7.6 Above-Grade (Elevated) Enclosed Areas

7.7 Two-Level Enclosed Areas

7.8 Solid Perimeter Foundation Walls on which Manufactured Homes Are Installed

7.9 Accessory Structures

8 Requirements and Guidance for Installation of Flood Openings

8.1 Location and Minimum Number of Flood Openings

8.2 Height of Flood Openings Above Grade or Floor

8.3 Examples of Flood Opening Installations

8.3.1 Interior Grade or Floor Higher than the Exterior Grade

8.3.2 Sloping Sites

8.3.3 Buildings with Large Enclosed Areas

8.3.4 Townhouses with Limited Exterior Walls

ii NFIP TECHNICAL BULLETIN 1 MARCH 2020

8.3.5 Buildings with Multiple Enclosures

8.3.6 Flood Openings in Areas with Shallow Flooding

9 Non-Engineered Flood Openings and Engineered Flood Openings

9.1 Measures Not Acceptable as Flood Openings

9.2 Non-Engineered Flood Openings

9.3 Engineered Flood Openings

9.3.1 Design and Performance Requirements

9.3.2 Documentation of Engineered Openings for Compliance

9.3.3 Engineered Openings with Certification Reports

9.3.4 Engineered Openings Individually Certified for Specific Buildings

9.3.5 NFIP Elevation Certificate and Documentation of Engineered Openings for Flood Insurance

10 References

List of Figures Figure 1: Equalizing flood forces (hydrostatic loads) on exterior walls

Figure 2: Typical enclosures with flood openings in Zone A

Figure 3: Full-height, solid perimeter walls surrounding a garage and storage area with flood openings

Figure 4: Backfilled stem wall foundation; flood openings not required

Figure 5: Limitations on below-grade crawlspaces in shallow flood hazard areas

Figure 6: Engineered openings in garage doors

Figure 7: Enclosure with flood openings under a house elevated on pilings

Figure 8: Above-grade enclosures

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

Figure 10: Manufactured home supported on interior piers and masonry perimeter wall with flood openings

Figure 11: Foundation plan of home with multiple enclosed areas, each with flood openings

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)

Figure 13: Flood openings in enclosure walls on a sloping site

Figure 14: Flood openings that are stacked and closely grouped to satisfy the required total net open area

NFIP TECHNICAL BULLETIN 1 MARCH 2020 iii

Figure 15: Suggested flood openings in enclosures under elevated townhouses

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

Figure 17: Standard air vent that is unacceptable as a flood opening because it is not disabled in the open position

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

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

Figure 20: Typical air vents with insect screens blocked by flood debris

Figure 21: Examples of typical air vents in crawlspace foundation walls used as flood openings with varying net open areas

Figure 22: Decorative masonry units and closely spaced holes in brickwork; the area of each hole counts toward the total net open area

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 24: Wood frame with insect screen inserted in void in poured concrete foundation wall;

inside dimensions of frame determine net open area

Figure 25: Equation used to determined total net area of engineered openings

Figure 26: Completing the NFIP Elevation Certificate when engineered openings are used

List of Tables Table 1: Comparison of Selected 2018 IRC and NFIP Flood Opening Requirements

Table 2: Comparison of Selected 2018 IBC and ASCE 24-14 Flood Opening Requirements with NFIP Requirements

Table 3: Flood Opening Coefficient of Discharge iv 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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• 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 definitions 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 flood 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 floor subgrade (below ground level) on all sides. NFIP regulations do not allow basements to extend below the base flood elevation (BFE) except in dry-floodproofed, non-residential buildings.

• Enclosed area (enclosure): An area below an elevated building that is enclosed by walls on all sides.

• Lowest floor: Lowest floor of the lowest enclosed area of a building, including basement. An unfinished or flood-resistant enclosure that is used solely for parking of vehicles, building access, or storage is not the lowest floor, provided the enclosure is built in compliance with applicable requirements.

• Net open area: Permanently open area of a non-engineered flood opening.

• Special Flood Hazard Area (SFHA): Area subject to flooding by the base flood (1-percent-annual-chance flood) 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.

4 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 officials 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 flood hazard areas.

Substantial Improvement and Substantial Damage. As part of issuing permits, local officials 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 definitions 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 officials 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 retrofit the enclosures to conform to current requirements for enclosures, even when the enclosure is below grade on all sides. Lower NFIP flood insurance rates may apply if retrofit enclosures have flood openings that meet the requirements in this Technical Bulletin and other requirements for enclosures (e.g., limited use, flood 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.

https://www.fema.gov/building-code-resources

6 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 flood elevation, including crawlspaces, to have flood 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 specificity:

measurement of enclosed area and minimum dimensions of opening.

Installation of flood openings

Section R322.2.2.1 Installation of openings.

Specifies the following for the installation of flood 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 final interior grade (or floor) and the finished 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 specificity than NFIP 44 CFR § 60.3(c)(5): openings on different sides, openings installed above higher of interior and exterior grade or floor, 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 flood loads to have flood 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.

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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

Certification of engineered openings

Section 1612.4(1.2).

Requires submission of a certification statement that the design provides for equalization of hydrostatic flood forces in accordance with ASCE 24, Section 2.7.2.2 (for engineered openings), if flood 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.

Specifies non-engineered openings, requires enclosed areas to be measured on the exterior, specifies 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: Specifies measurement of enclosed areas to determine square footage. Clarifies that the presence of louvers, blades, screens, faceplates, and devices must be accounted for in the measurement of net open area of flood openings.

Equivalent to

NFIP 44 CFR

§ 60.3(c)(5) but with more specificity:

measurement of enclosure area, minimum dimension of openings, and measurement of net open area.

Engineered openings

ASCE 24 Section 2.7.2.2.

Specifies 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 flood 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. Specifies 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 coefficients of discharge

Equivalent to

NFIP 44 CFR

§ 60.3(c)(5) but with more specificity:

minimum rate of rise and fall, minimum dimension of openings, and formula for engineered openings.

Installation of flood openings

ASCE 24 Section 2.7.3.

Specifies 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 final interior grade or floor and the finished 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 clarifies that the position is relative to the higher of the interior and exterior grade or floor.

Equivalent to

NFIP 44 CFR

§ 60.3(c)(5) but with more specificity:

openings on different sides, bottom of openings above higher of interior and exterior grade or flood, and openings in doors and windows.

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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 Certificate should be used to note characteristics of enclosures and flood 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 officials and insurance agents may inadvertently determine that enclosures are non-compliant and deem the floor of the enclosure the lowest floor, resulting in unnecessarily high NFIP flood 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 flood openings are non-residential buildings that are engineered to be dry floodproofed. For information on dry floodproofing, 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-floodproofed basements in specific circumstances.

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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 flood insurance rates.

NFIP TECHNICAL BULLETIN 1 MARCH 2020 11

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 flood 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 Certificate for a building elevated on a backfilled 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 flood 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 specific provisions in their ordinances to be consistent with the limitations specified in NFIP Technical Bulletin 11. Communities should consult NFIP State Coordinators or FEMA Regional Offices 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), specifies that the installation of skirting does not trigger the requirement for flood 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 flood 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 floodplain management and NFIP flood 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 flood openings (but flood openings may be provided). The utility chase must be constructed of flood damage-resistant materials below the BFE, and the enclosed utility lines must meet the requirement to be watertight and capable of withstanding flood 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 flood openings in all breakaway walls, including those in Coastal A Zones and Zone V.

Post-flood assessments indicate that breakaway walls with openings prevent wall failure under frequent, shallow flood 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 flood insurance policies for elevated buildings with above-grade enclosures are rated assuming the above-grade enclosure is the lowest floor (i.e., the floor of the enclosure instead of the floor 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 flood insurance premiums than enclosures with floors 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 flood insurance premium than if the building has a one-level enclosure. Even if a two-level enclosure complies with building codes and floodplain management requirements for enclosures, the upper floor of the two-level enclosure will be deemed the lowest floor for insurance rating purposes (the lowest floor for flood insurance purposes is the first floor 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…