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Openings in FoundationWalls and Walls ofEnclosuresBelow Elevated Buildings in Special Flood Hazard Areasin accordance with the National Flood Insurance Program

Technical Bulletin 1 / August 2008


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Comments on the Technical Bulletins should be directed to:

Department o Homeland Security

FEMA Mitigation Directorate500 C Street, SW.

Washington, D.C. 20472

Technical Bulletin 1-08 replaces Technical Bulletin 1-93, Openings in Foundation Walls.

Photograph Credits:

Figure 3. Bill Bryant, Anne Arundel County, Maryland

Figure 4. Smart Vent, Inc.

Figure 17. North Carolina Emergency Management/T. Riddle

Table o Contents

Introduction ..................................................................................................................................1

NFIP Regulations ..........................................................................................................................4

How Openings Aect Flood Insurance Rates ..............................................................................4Documenting Elevations and Inormation About Openings .................................................... .5

Enclosed Areas Below Elevated Buildings ....................................................................................5

Enclosures That Require Openings ..................................................................................6

Situations That Do Not Require Openings ....................................................................12

Requirements and Guidance or Installation o Openings .......................................................13

Minimum Number o Openings .....................................................................................13

Height o Openings Above Grade ..................................................................................14

Installation Examples ......................................................................................................15

Non-Engineered Openings and Engineered Openings ............................................................18

Unacceptable Measures ...................................................................................................19

Non-Engineered Openings .............................................................................................20

Engineered Openings .....................................................................................................24

The NFIP ......................................................................................................................................28

NFIP Technical Bulletins ............................................................................................................28

Ordering Technical Bulletins .....................................................................................................28

Further Inormation ...................................................................................................................29

Glossary ........................................................................................................................................30


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1Technical BulleTin 1 augusT 2008

Introduction

Protecting buildings that are constructed in special ood hazard areas (SFHAs) rom dam-age caused by ood orces is an important objective o the National Flood Insurance Program(NFIP). In support o this objective, the NFIP regulations include minimum building de-

sign criteria that apply to new construction, repair o substantially damaged buildings, andsubstantial improvement o existing buildings in SFHAs. The base ood is used to delineateSFHAs on Flood Insurance Rate Maps (FIRMs) prepared by the NFIP. The base ood is theood that has a 1-percent chance o being equaled or exceed-ed in any given year (commonly called the 100-year ood).Certain terms used in this Technical Bulletin are defned inthe Glossary.

The NFIP regulations require that residential buildingsconstructed in A zones have the lowest oor (including base-ment) elevated to or above the base ood elevation (BFE). In

this Technical Bulletin, the term A zones includes all zonesshown on FIRMs as Zones A, AE, A1-A30, AR, AO, and AH.

Enclosed areas (enclosures) are permitted under elevatedbuildings provided the enclosed areas meet certain use re-strictions and construction requirements related to oodresistance, including use o ood damage-resistant materialsand installation o openings to allow or automatic entry andexit o oodwaters. Enclosures under buildings in V zones(includes all Zones V, VE, and V1-V30) must meet the same en-closure requirements except that openings are not required

and walls must be non-supporting breakaway walls, open lat-tice-work, or insect screening (see Technical Bulletin 9,Designand Construction Guidance or Breakaway Walls Below ElevatedCoastal Buildings).

The NFIP regulations or new construction and substantialimprovements o existing buildings require that enclosed ar-eas under elevated non-residential buildings meet the samerequirements as those or enclosures under elevated residen-tial buildings. New non-residential buildings constructed in Azones, and substantial improvements o existing non-residen-

tial buildings, must either have their lowest oors elevated toor above the BFE or be oodprooed (made watertight) to orabove the BFE.

Many types o oundations are used to elevate buildings. Whilethe main portions o elevated buildings are above the BFE,the oundation and any enclosed areas below the BFE willbe exposed to ood orces. Enclosed areas below the BFE

Under the NFIP, the low-est oor is the oor o the

lowest enclosed area oa building. An unfnished

or ood-resistant enclo-sure that is used solely or

parking o vehicles, build-ing access, or storage is

not the lowest oor, provid-ed the enclosure is built incompliance with applicable

requirements.

As used by the NFIP, an

enclosure is an area thatis enclosed on all sides by

walls.

The NFIP defnes a base-

ment as any area that isbelow-grade on all sides.

The regulations do not allowbasements to extend belowthe BFE.

Owners o existing elevatedbuildings with enclosures

below the BFE may wishto retroft the enclosures.

Lower NFIP ood insur-ance rates may apply i the

retroft enclosures haveopenings that meet the re-

quirements in this TechnicalBulletin and also meet otherrequirements or enclosures

(limited use, ood dam-age-resistant materials, and

elevated utilities).


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2 Technical BulleTin 1 augusT 2008

(including crawlspaces) are permitted i used only or parking o vehicles, building access,and storage. Figure 1 illustrates a typical crawlspace oundation wall and a typical ramed wallsurrounding an enclosed area.

I enclosure walls are not designed with openings to relieve the

pressure o standing or slow-moving water against them (calledhydrostatic loads), the walls can be damaged or ail during aood. I the walls are load-bearing walls that support the el-evated building, ailure o the walls may result in damage to,or collapse o, the building. To address this concern, the NFIPregulations require that enclosure walls contain openings thatwill allow or the automatic entry and exit o oodwaters. Theseopenings allow oodwaters to reach equal levels on both sideso the walls, thereby lessening the potential or damage causedby a dierence in hydrostatic loads on opposite sides o thewalls. In A zones, the requirement or ood openings applies

to all enclosed areas below new elevated buildings and belowsubstantially improved buildings.

This Technical Bulletin explains the NFIP requirements or ood openings and providesguidance or prescriptive (non-engineered) openings and engineered openings. Non-engi-neered openings are used to meet the NFIPs prescriptive requirement o 1 square inch o netopen area or every square oot o enclosed area. As an alternative, engineered openings thathave characteristics that dier rom non-engineered openings may be used provided they aredesigned and certifed by a registered design proessional as meeting certain perormancecharacteristics described in this Technical Bulletin.

Areas o shallow ood-

ing may be shown as AO

zones on FIRMs. Ratherthan BFEs, AO zones haveood depths that range

rom 1 to 3 eet. In thesezones, all NFIP require-ments related to BFEs

apply, including elevation othe lowest oor to or above

the designated ood depthand requirements or enclo-

sures with ood openingsthat are located so that

oodwaters will ow in andout.

Figure 1. Typical enclosures with ood openings


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This Technical Bulletin also discusses how openings could aect ood insurance premiums,provides examples o enclosures that require openings and situations where openings are notrequired, and outlines the requirements or, and provides guidance on, the ollowing:

n Installation o openings, including the minimum number o openings and height o open-ings above grade,

n Non-engineered openings, and

n Engineered openings.

Examples are provided to illustrate types o buildings and enclosures that require openings,and to address several commonly encountered situations. Other situations may require the ad-vice o a registered design proessional. Questions should be directed to the appropriate localofcial, NFIP State Coordinating Ofce, or FEMA Regional Ofce.

Solid perimeter oundation walls and walls surrounding en-closed areas below the BFE may be damaged by orces related

to moving oodwaters and wave impacts (called hydrodynamicloads), and debris impacts. The requirement or openings isintended to reduce only ood damage associated with hydro-static not hydrodynamic loads.

Hydrodynamic loads and debris impacts may be signifcant insome ood hazard areas shown as A zones on FIRMs, includ-ing riverine areas where high ow velocities are likely (e.g.,aster than 5 eet per second) and areas where wave heights o1.5 eet or more are possible. In these areas, it is recommend-ed that a registered design proessional evaluate oundation

designs. Open oundations without enclosed areas are less vul-nerable to the type o damage that can be caused by high owvelocities and wave action.

Buildings in V zones (Zones V, VE, and V1-V30) must meet certain design and constructionrequirements that are specifed in the NFIP regulations at Section 60.3(e). The area below thelowest oors o buildings in V zones must be ree o obstruction or, i enclosed, the walls oenclosures must be constructed with non-supporting breakaway walls, open wood lattice-work,or insect screening. Openings may be provided, but are not required, in breakaway walls un-der buildings in V zones. For inormation on V-zone design and construction requirements,reer to the NFIP regulations, the Technical Bulletin series (especially Technical Bulletin5, Free-o-Obstruction Requirementsand Technical Bulletin 9, Design and Construction Guidance or Breakaway Walls Below Elevated Coastal Buildings), the Coastal Construction Manual(FEMA55CD), Flood Resistant Design and Construction(ASCE 24), and Home Builders Guide to CoastalConstruction(FEMA 499).

This Technical Bulletin dis-cusses openings in walls

below the BFE. Readersshould check with the

community to determinewhether a higher eleva-

tion standard is enorced.For example, communi-ties may add reeboard or

may regulate to the designood elevation (DFE). In

those cases, reerences tothe BFE in this Technical

Bulletin should be con-

strued as reerences tothe communitys elevation

requirement.


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NFIP Regulations

The NFIP regulations or enclosures are codifed in Title 44 o the Code o Federal Regula-tions, in Section 60.3(c)(5), which states that a community shall:

Require, or all new construction and substantial improvements, that ully enclosed ar-eas below the lowest oor that are usable solely or parking o vehicles, building access,or storage in an area other than a basement and which are subject to ooding shall be

designed to automatically equalize hydrostatic ood orces on exterior walls by allowingor the entry and exit o oodwaters. Designs or meeting this requirement must either becertifed by a registered proessional engineer or architect or meet or exceed the ollowingminimum criteria: A minimum o two openings having a total net area o not less thanone square inch or every square oot o enclosed area subject to ooding shall be provided.The bottom o all openings shall be no higher than one oot above grade. Openings may

be equipped with screens, louvers, valves, or other coverings or devices provided that theypermit the automatic entry and exit o oodwaters.

Proposals or substantial improvement o existing buildings in SFHAs, and proposals to repairthose that have sustained substantial damage, must comply with the requirements or newconstruction. In A zones, the applicable requirements include openings in the walls surround-ing enclosed areas below the BFE. As part o issuing permits, community ofcials must reviewsuch proposals to determine whether they comply with the requirements. Further inorma-tion on substantial improvement and substantial damage is ound in Answers to Questions AboutSubstantially Damaged Buildings(FEMA 213).

How Openings Aect Flood Insurance Rates

Careul attention to compliance with the NFIP regulations or ood openings is importantduring design, plan review, construction, and inspection. Compliance inuences both the

vulnerability to ood damage and the cost o NFIP ood insurance. I openings are not com-pliant, the oor o the crawlspace or the oor o the enclosure becomes the lowest oor. Inthose cases, the result may be signifcantly higher ood insurance premiums, especially i theoor o the crawlspace or enclosure is more than a oot or two below the BFE.

The NFIP Technical Bulletins provide guidance on the minimum requirements o the NFIP regulations.

Community or State requirements that exceed those o the NFIP take precedence. Design proes-sionals should contact the community to determine whether more restrictive provisions apply to thebuilding or site in question. All other applicable requirements o the State or local building codes must

also be met or buildings in ood hazard areas.


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Documenting Elevations and Inormation About Openings

Communities are required to collect data rom permittees to document the surveyed elevationo the lowest oors o new buildings and existing buildings that are substantially improved.Although the data may be provided in other ormats, the NFIPs Elevation Certifcate (FEMA

Form 81-31) is designed specifcally or this purpose. The current version o the Elevation Cer-tifcate is online at http://www.ema.gov/business/nfp/elvinst.shtm.

The Elevation Certifcate is designed to collect inormation that acilitates determining com-pliance o new construction and to provide data necessary or the proper rating o NFIP oodinsurance. For guidance, see the instructions that accompany the Elevation Certifcate andthe Floodplain Management Bulletin: Elevation Certifcate(FEMA 467-1).

The Elevation Certifcate has blanks that are to be completed i there are enclosures underelevated buildings, including:

n

The square ootage o the enclosed area,n The number o ood openings within 1.0 oot above adjacent grade, and

n The total net area o ood openings.

The Elevation Certifcate provides space or comments. As noted above and explained in moredetail below, the regulations provide two ways to satisy the requirements or openings. Com-ments should be provided when engineered openings are used, and when there are otheraspects o enclosures and openings that comply with the requirements but that, without closeinspection, may appear to be non-compliant. The documentation required or engineeredopenings should be attached to the Elevation Certifcate (described on page 25, Documenta-

tion o engineered openings or ood insurance).

Enclosed Areas Below Elevated Buildings

The NFIP regulations speciy that enclosed areas under elevated buildings may be allowedprovided the enclosed areas are used solely or:

n Parking o vehicles (attached garages or parking areas be-low elevated buildings)

n Building access (stairwells, oyers, elevators)

n Storage (low-value items)

Although crawlspaces are not listed explicitly as an allowableuse, buildings may be elevated using perimeter oundationwalls that create enclosed areas, typically called crawlspaces orunder-oor spaces. Crawlspaces provide access to under-oorutilities such as pipes, ductwork, and electric conduits.

Some communities requirepermittees to execute anon-conversion agreement

to document their under-standing that the use o

enclosures is limited, thatconversion to other uses is

not allowed, and that modi-fcation o enclosures may

result in higher NFIP oodinsurance rates.


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It is important to understand how an otherwise compliant en-closed area below the BFE can be rendered non-compliant byinstalling eatures that are not consistent with the limitationson uses. The ollowing are not allowed below the BFE becauseo potential damage and their presence is inconsistent with

the allowed uses: appliances, heating and cooling equipment,plumbing fxtures, more than the minimum electric servicerequired to address lie saety and electric code requirementsor building access and storage areas, and materials that arenot ood damage-resistant.

The NFIP regulations require that enclosed areas surroundedby solid walls that extend below the BFE have ood open-ings. The requirement applies whether the walls are load-bearing walls or non-load-bearingwalls. Thereore, openings are required in solid perimeter oundation walls that surroundcrawlspaces and openings are required in the walls o ully enclosed areas that meet the use

limitations (parking o vehicles, building access, or storage). The requirement applies to newconstruction and to buildings that are undergoing substantial improvement, including repairo substantial damage.

Enclosures That Require Openings

Several examples o enclosures that require openings are described below:

n Solid perimeter oundation walls (crawlspaces or under-oor spaces)

n Solid perimeter oundation walls (below-grade crawlspaces)

n Solid perimeter oundation walls (with ull-height under-oor spaces)

n Garages attached to elevated buildings

n Enclosed areas under buildings elevated on open oundations in A zones

n Enclosed areas with breakaway walls under buildings elevated on open oundations in Azones

n Solid perimeter oundation walls on which manuactured homes are installed

n Accessory structures (detached garages and storage sheds)

Solid perimeter oundation walls (crawlspaces or under-oor

spaces)The crawlspace or under-oor space that is created when abuilding is elevated on a solid perimeter oundation wall is anenclosed area below the BFE that must meet all o the require-ments or enclosed areas (reer to Figure 1). I a brick veneer,siding, or other material covers the wall, then the openingsmust completely penetrate into the enclosed area. A crawlspaceaccess with a door does not qualiy as a ood opening unless

In many parts o the coun-

try, a common practice isto build conditioned crawl-spaces that are sealed and

have mechanical ventilation.In SFHAs, all crawlspacesmust have ood openings

that meet the requirementso the NFIP and the building

codes.

The only exception to theopenings requirement is

or non-residential build-ings that are engineered to

be oodprooed by meetingstringent requirements to

be watertight. For inorma-tion on oodproofng, reerto Technical Bulletin 3, Non-

Residential Floodproofng Requirements and

Certifcation.


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the door has an opening installed in it or otherwise meets the perormance requirement thatit will allow automatic entry and exit o oodwaters.

As explained on page 14 (Height o Openings Above Grade), the bottom o each opening isto be located no higher than 1 oot above the higher o the fnal interior or exterior grades

under the opening. Thereore, placement o the openings in the oundation wall requiresknowledge o the expected fnished exterior grade and the fnal interior grade o the crawl-space.

Building code requirements may call or ventilation o certain under-oor spaces. Ventilationopenings typically are positioned near the top o the oundation wall to acilitate air ow. Inmost cases, ventilation openings will be too high above grade to satisy the requirements orood openings.

Solid perimeter oundation walls (below-grade crawlspaces)

The NFIP regulations do not allow buildings to be constructed

with areas that are below grade on all sides (basements), ex-cept or certain engineered non-residential buildings that aredesigned and certifed to be oodprooed. Thereore, crawl-spaces that are below-grade on all sides are not allowed becausethey are basements. An exception is available only in shallowoodplains, and then only i certain other requirements andlimitations are met. Those requirements and limitations aredetailed in Technical Bulletin 11, Crawlspace Construction or Buildings Located in Special FloodHazard Areas: National Flood In-surance Program Interim Guidance. According to this guidance, be-

low-grade crawlspaces may beallowed provided the wall heightis less than 4 eet when measuredrom bottom o the oor joist/truss to the top o ooting, whichmust be no more than 2 eet be-low-grade (see Figure 2). Floodopenings are required in theoundation walls surroundingthese crawlspaces and, as notedabove, air ventilation may be re-quired.

Although crawlspaces that satisythe limitations in TB 11 are notconsidered basements or ood-plain management purposes, itis important to note that theyare basements or NFIP ood

Communities are requiredto adopt specifc provi-sions in their ordinances

to be consistent with thelimitations in TB 11 in or-

der to permit below-gradecrawlspaces.

Figure 2. Limitations on below-grade crawlspaces in shallow

ood hazard areas (TB 11)


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insurance purposes. Thereore, NFIP ood insurance will be more expensive i the grade insidethe crawlspace is below the exterior grade on all sides. In addition, below-grade crawlspacesmay contribute to increased humidity and mold growth. TB 11 requires that an adequatedrainage system be provided in order to minimize oodwater contact with crawlspace materi-als and related moisture damage.

Solid perimeter oundation walls (with ull-height under-oor spaces)

In SFHAs where the BFE is more than 4 or 5 eet above grade, or where owners want enoughhead room to allow or parking o vehicles and storage, solid perimeter oundation walls maybe used to create ull-height under-oor spaces (see Figure 3). The walls surrounding the un-der-oor space must meet all o the opening requirements.

It is important that ull-height under-oor spaces also meet all other NFIP requirements tominimize the likelihood o uture conversion to uses other than the allowed uses (parkingo vehicles, building access, or storage). As noted in the discussion o limitations on uses oenclosures, the ollowing are not allowed below the BFE in ull-height enclosures because o

potential damage and their presence is inconsistent with the allowed uses: appliances, heatingand cooling equipment, plumbing fxtures, more than the minimum electric service requiredto address lie saety and electric code requirements or building access and storage areas, andmaterials that are not ood damage-resistant.

Garages attached to elevated buildings

Many buildings, especially homes, are designed with attached garages. An attached garagemay have its oor below the BFE provided the garage meets all o the requirements or an en-closed area below the BFE. The use o the garage space must be limited to parking o vehicles,building access, and storage.

Figure 3. Full-height

solid perimeter walls

surrounding garage and

storage area (only two

openings visible)

Flood openings(only 2 shown)


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Openings are required in the exterior walls o the garage, and openings may be installed inexit doors and garage doors (see Figure 4). It is important to note that garage doors them-selves do not meet the requirements or openings. Human intervention would be necessaryto open garage doors when ooding is expected, which is inconsistent with the requirementthat openings allow or the automatic entry and exit o oodwaters. Similarly, gaps that may

be present between the garage door and the door jamb or walls do not guarantee automaticentry and exit o oodwaters and do not count towards the net open area requirement.

I an attached garage is built with its oor below the BFE and it does not have compliantopenings, the garage oor becomes the lowest oor. Flood insurance premiums may be sig-nifcantly higher than i the garage complies with the requirements or openings and otherrequirements, such as ood damage-resistant materials and elevated utilities.

Enclosed areas under buildings elevated on open oundations in A zones

A building that is elevated on an open oundation (e.g., piers, posts, columns, or pilings) in anA zone may have enclosed areas below the elevated oor (see Figure 5). Sometimes only parto the ootprint is enclosed, such as or a stairwell or storage room. All o the requirements orenclosed areas apply, including openings, elevated utilities, ood damage-resistant materials,and limitations on use (parking o vehicles, building access,and storage).

Open oundations are recommended in riverine ood haz-ard areas where ow velocities are expected to exceed 5 eetper second because o the anticipated hydrodynamic loadsand potential or debris impact and scour. These loads maybe sufcient to damage typical solid perimeter oundationwalls, even though ood openings are provided.

Figure 4. Attached

garage, with engineered

openings installed in the

garage door

Flood openings

ASCE 24 and several o

the act sheets included inthe Home Builders Guideto Coastal Construction

(FEMA 499) are excellentresources or ood-resistant

building methods in coastalA hazard areas.


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I a waterway was studied using detailed methods and a oodway is shown on a FIRM, thenthe Floodway Data Table in the Flood Insurance Study should be reviewed or data that canbe used to estimate velocities. For each cross section, the table provides the mean velocity thatcan be used to approximate velocities in the oodplain outside o the oodway. For other wa-terways in areas known to have ast-moving water, standard methods can be used to compute

an approximate velocity. Examples o other sources o inormation that should be reviewedinclude local observations and studies prepared by State and local agencies.

Enclosed areas with breakaway walls under buildings elevated on open oundations in A zones

Open oundations are also recommended in A zones in coastal areas where breaking waveheights can be between 1.5 and 3.0 eet (called Coastal A Zones). In these areas, it is recom-mended that walls surrounding enclosed areas be designed as breakaway walls. Flood openingsare required in breakaway walls in A zones in order to comply with the NFIP requirements.ASCE 24 includes specifc provisions or openings in breakaway walls.

Solid perimeter oundation walls on which manuactured homes are installed

Manuactured homes may be installed on solid perimeter oun-

dation walls that enclose space below the homes (see Figure 6).Even i it is not part o the load-bearing oundation, a solidperimeter wall is required to have openings, otherwise hydro-static loads may damage the perimeter wall, which could, inturn, damage the homes supporting oundation and anchorsystem.

Figure 7 shows an example o a ramed enclosure below an ele-vated manuactured home. In this case, the ull-height enclosed

Openings are required inrigid skirting that is attachedto rames or oundations o

manuactured homes to re-lieve hydrostatic loads and

minimize transerring loadsthat can damage homes

and their supporting oun-dation systems.

Figure 5. Enclosure with ood

openings, under house elevated on

pilings


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area is used or parking and storage. Openings are required because the walls surroundingthe enclosed area are solid walls. As indicated by the driveway on the let, the interior slab ishigher than the exterior grade along the side o the building. The openings shall be locatedwithin 1 oot o the interior grade.

Figure 6. Manuactured homesupported on piers; masonry perimeter

wall with ood openings (ground

anchors not shown)

Figure 7. Manuactured

home installed above

a ull-height ramed

garage (note elevation

o driveway slab on let;

the openings are within

1 oot o interior grade o

the slab)


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Accessory structures: detached garages and storage sheds

Detached garages and detached storage buildings in A zones may be permitted without requir-ing them to be elevated i they comply with all o the requirements or enclosures. Garagesand other accessory buildings must be used only or parking o vehicles and storage, utilitiesmust be elevated, ood damage-resistant materials must be used below the BFE, the require-

ments or ood openings must be satisfed, and they must be anchored to resist otation,collapse, or lateral movement under ood conditions.

Communities are required to regulate all development in SFHAs, including the placement osmall storage sheds. Storage sheds in A zones are not required to be elevated i they complywith all o the requirements or enclosures. They must be used only or storage, utilities mustbe elevated, ood damage-resistant materials must be used below the BFE, and the require-ments or ood openings must be satisfed. In addition, sheds are to be anchored to preventotation, collapse, or lateral movement under ood conditions.

Situations That Do Not Require OpeningsTwo situations that do not require openings are described below:

n Manuactured home with skirting

n Back-flled stem wall oundation

Manuactured home with exible skirting

Skirting used to enclose the area under manuactured homestypically is made o weather-resistant material and extendsrom the bottom o the home down to grade. Flexible skirt-

ing and rigid skirting that are not attached to the rame oroundation o a manuactured home are not required tohave openings. However, where oodwaters are expected torise rapidly, there may be concerns about the skirting beingpushed against oundation systems. In these areas, open lat-tice may be more appropriate to minimize the potential orood damage.

Filled stem wall oundation

A flled stem wall oundation (also called a chain wall) canlook like a solid perimeter oundation wall rom the outside,but this type o oundation is backflled with compacted struc-tural fll that supports the oor slab (see Figure 8). Because o the fll, unbalanced lateralloads against the walls will be minimized as oodwaters, and thus openings are not required.

It is important that the fnal Elevation Certifcate, or other documentation o elevations, in-clude an explanation when stem wall oundations are used to avoid the assumption that itis a crawlspace that lacks the required openings. The Elevation Certifcate diagrams do notillustrate flled stem wall oundations. A note in the comment section should describe theoundation so that insurance agents are alerted as to why there are no openings.

The National Fire Protection

Associations standard,Model Manuactured HomeInstallation Standard(NFPA

225), specifes that instal-

lation o skirting does nottrigger the requirement orood openings provided

the skirting does not pro-vide structural support andwill collapse under wind and

water loads that are lessthan those expected during

the base ood event withoutcausing structural damage

to the elevated home or theoundation.


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Requirements and Guidance or Installation o Openings

The NFIP regulations speciy certain installation requirements that must be met by all oodopenings, whether non-engineered openings or engineered openings, which are describedstarting on page 18. The installation requirements address the minimum number o openingsand the maximum height o openings above grade. Additional guidance and explanations or

various situations are described below.

Minimum Number o Openings

Each enclosed area is required to have a minimum o two openings on exterior walls to allowoodwaters to enter directly. In order to meet the requirement, the openings must be locatedso that the portion o the opening intended to allow or inow and outow is below the BFE.Openings that are entirely above the BFE (or any portion o an opening that is above the BFE)will not serve the intended purpose during base ood conditions and thus are not countedtowards the compliance with the ood opening requirements.

The openings should be installed on at least two sides o eachenclosed area to decrease the chances that all openings couldbe blocked with oating debris and to allow or more evenflling by oodwater and draining o the enclosed area. It isrecommended that openings be reasonably distributed aroundthe perimeter o the enclosed area unless there is clear justif-cation or putting all openings on just one or two sides (suchas in townhouses or buildings set into sloping sites).

Figure 8. Back-flled stem wall

oundation (openings not required)

The InternationalResidential Codeand the

International Building Code(by reerence to ASCE 24)both require a minimum

o two openings on dier-ent sides o each enclosed

area.


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Figure 9 shows a sketch illustrating where openings could be located when an elevated build-ing has multiple enclosed areas. [Note: the number o openings shown in Figure 9 is orillustration only; the total number o openings and the adequacy o the net open area o thoseopenings depend on the type o opening, covering, and whether vent devices or engineeredopenings are installed.]

Height o Openings Above Grade

The bottom o each opening is to be located no higher than 1 oot above the grade that isimmediately under each opening. The purpose o this requirement is to satisy the peror-mance expectation that the dierence in water levels between the interior and exterior willnot exceed 1 oot as water begins to rise and as oodwaters recede rom the site. Note that theopenings (or those portions that count towards the required net open area) must be locatedbelow the BFE. In areas with shallow ood depths, this may require positioning the openingscloser to grade than the maximum 1 oot allowed.

Given the requirement that the bottom o openings shall not be higher than 1 oot abovegrade, a question arises i the interior and exterior grades are dierent: which grade shouldbe used to determine placement o ood openings? The higher o the fnal interior gradeand the fnished exterior grade that is immediately under each opening is used to make thisdetermination:

n Finished exterior grade. Care should be taken when placing backfll, topsoil, and land-scaping materials around the outside o enclosures, especially solid perimeter oundation

Figure 9. Sketch o oundation plan o home with multiple enclosed areas, each with ood openings

(number o openings or illustration purposes only)


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walls. I the fnished exterior grade is higher than the interior grade on all sides o thebuilding, then the enclosed area becomes a basement as defned by the NFIP.

n Final interior grade. The trench that is excavated to construct ootings and oundationwalls must be backflled completely, otherwise a basement is created. I the interior gradeis higher than the exterior grade, the openings are to be no higher than 1-oot above the

interior grade.

Installation Examples

Interior grade higher than exterior grade

Consider a crawlspace enclosure that has its interior grade higher than the exterior grade. Aswater rises against the outside o the oundation, the ground or fll on the interior balancesthe hydrostatic load (see Figure 10). It is only when the water rises above the interior gradethat the lateral load becomes unbalanced and thereore must be equalized by openings.

When viewed rom the outside, a solid perimeter oundation wall or wall surrounding an en-closed area with the interior grade higher than the exterior grade will appear to not meet theinstallation requirements or openings. The openings will appear to be too high above the ex-terior grade (illustrated in Figure 7). Thereore, it is important that the fnal documentationo as-built elevations note the dierence in interior and exterior grades. For example, i theNFIP Elevation Certifcate is used, comments should explain that the interior grade is higherthan the exterior grade and it should be noted whether the openings are (or are not) within1 oot o the higher o the two grades.

Figure 10 . Illustration o oodopenings installed within 1 oot o the

higher o interior or exterior grade


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Sloping sites

Buildings on solid perimeter oundation walls that are set into a sloping site present anotherspecial situation with respect to installation o openings. Careul attention must be paid to theollowing:

n

The interior oor along the lower side o a building that is set into a sloping site must beat or above the exterior grade across the entire length o that side o the building, other-wise the enclosure becomes a basement.

n The bottom o each opening shall be located no higher than 1 oot above the exterior orinterior grade immediately below the opening, whichever is higher (see Figure 11).

n For openings to perorm their intended unction, sufcient open area must be below theBFE.

Townhouses with limited exterior walls

Townhouses are single-amily dwelling units constructed in a group o three or more attachedunits in which each unit extends rom oundation to roo and with exterior walls on at leasttwo sides. Openings are required i townhouses in SFHAs are constructed with solid perimeteroundation walls or with solid walls surrounding enclosed areas under the elevated portion othe building.

Because the interior townhouse units have less linear exterior wall length than the end units,it can be a challenge to meet all o the requirements, especially the requirement or adequatenet open area and the requirement that each enclosed area have openings. I openings can-not be provided in at least two walls, the NFIP allows all openings to be installed in one wall.

Figure 11. Openings in enclosure

walls, sloping site


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Design o interior townhouse units can satisy the guidance that openings should be on dier-ent sides i the walls inside the enclosed area have openings to connect enclosed spaces romront to back. Figure 12 shows suggested locations or openings. [Note: the number o open-ings shown in Figure 12 is or illustration only; the total number o openings and the adequacyo the net open area depend on the type o opening, covering, and whether a vent device is

installed in the openings.]

It may be even more challenging to provide adequate openings in enclosures under interiortownhouse units i the multi-unit building is set into a sloping site, in which case it may be ap-propriate to consider using a flled stem wall oundation or an open oundation. Use o fllacross one side o elevated townhouses may create a similar complication.

Openings that extend above the BFEOnly those portions o openings that are below the BFE can be counted towards the requirednet open area. Stacked vent devices may be installed or large-dimension openings may be pro-vided (Figure 13). In both cases, i the BFE does not reach the top o the opening, only theportion that is below the BFE will count as contributing to the required net open area. Simi-larly, i the oor o a mechanical room is below the BFE (with elevated equipment inside) anda louvered door provides ventilation, only the open portion o the louvered door that is belowthe BFE will count towards the required net area o ood openings.

Figure 12. Illustration o suggested ood openings in enclosures under elevated townhouses (number o

openings or illustration purposes only)


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Depth o water 1 oot or less

Some FIRMs show mapped SFHAs where the depth o water will be 1-oot deep or shallower.Although the dierence in water depth between the outside and inside o the enclosure un-der a building in these areas will not exceed 1 oot during the base ood, the NFIP regulations

require openings.

There are at least two solutions to this situation. The frst is to elevate the oor o the enclo-sure the necessary height so that it is at or above the BFE and there is no need or openings.The second solution is to install openings, taking care to ensure that all o the necessary openarea is below the BFE (otherwise the openings will not unction as intended). This can be ac-complished by positioning the bottom o the openings at or very close to grade, rather thanthe maximum o 1 oot above grade. In addition to complying with the regulations, the wallswill not experience excessive dierential hydrostatic pressure when oodwaters rise higherthan the BFE.

Non-Engineered Openings and Engineered Openings

The NFIP regulations identiy alternatives to provide sufcient size and number o openingsto allow or the automatic entry and exit o oodwaters. This section describes how this levelo perormance can be satisfed by use o:

n Non-engineered openings (or covers and devices) that meet the prescriptive require-ment to provide 1 square inch o net open area or each square oot o enclosed area (as

Figure 13. Stacked vents inserted in

large openings must be below the BFE


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described below, a variety o options and devices can serveas non-engineered openings).

n Engineered openings (or covers and devices) that arespecifcally designed and certifed by a registered designproessional as meeting the required perormance and

design requirements outlined below (and, i applicable,the communitys building code).

n Engineered openings (or covers and devices) or whichan Evaluation Report has been issued by the Internation-al Code Council (ICC) Evaluation Service, Inc. (ICC-ES),a subsidiary o the International Code Council, Inc.(http://www.iccsae.org).

The ollowing requirements or installation apply regardless o whether engineered openingsor non-engineered openings are used to satisy the NFIP requirements (also see page 13, Re-

quirements and Guidance or Installation o Openings):n Each enclosed area must have a minimum o two openings; i there are multiple enclosed

areas, each area must have openings in its exterior walls,

n The bottom o each opening must be no more than 1 oot above the higher o the interioror exterior grade immediately under the opening, and

n Any screens, grates, grilles, fxed louvers, or other covers or devices must not block or im-pede the automatic ow o oodwaters into and out o the enclosed area.

Unacceptable Measures

It is important to note that FEMA has determined that certain measures are not acceptable asood openings, including:

n Standard oundation air ventilation devices that can be closed manually, because they donot allow or the automatic entry and exit o oodwaters unless they are permanently dis-abled in the open position.

n Standard oundation air ventilation devices that have detachable solid covers that are in-tended to be manually installed over the opening in cold weather, because they do notallow or the automatic entry and exit o oodwaters when the cover is in place.

n Standard oundation air ventilation devices that are designed to open and close based on

temperature (unless they also are designed to allow or the automatic entry and exit ooodwaters).

n Windows below the BFE, because the automatic entry and exit o oodwaters cannot besatisfed by the expectation that windows will break under rising oodwaters.

n Garage doors without openings installed in them, because human intervention is requiredto open the doors when ooding is expected. Gaps between the garage door and the doorjamb or walls do not count towards the net open area requirement.

n Standard exterior doors without openings installed in them.

The InternationalResidential Code includes

both the prescriptive (non-engineered) alternative andthe engineered openings

alternative.

The International Building

Codealso includes bothalternatives by reerence to

ASCE 24.


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Non-Engineered Openings

Non-engineered openings are openings that are used to satisy the prescriptive requirementthat calls or 1 square inch o net open area or each square oot o enclosed area. A wide va-riety o options is available to satisy the prescriptive requirements.

The term net open area reers to the permanently open area o a non-engineered opening.The NFIP regulations indicate that ood openings may be equipped with coverings or devic-es provided that they permit the automatic entry and exit o oodwaters. The measuremento the net open area must take into consideration any coverings that have solid obstructions,such as grilles, fxed louvers, or aceplates. Figure 14 shows a typical standard air vent aceplateand measurements o the net open area.

Manuacturers o devices intended or use as standard air vents typically indicate the numbero square inches that each device provides or air ow (either stamped into the metal rame ornoted on the packaging). The same number should be used or the net open area calculationwhen these devices are installed as non-engineered openings. However, in order to qualiy asood openings that permit automatic entry and exit o oodwaters, openings must not havesolid covers that are installed during cold weather. Similarly, typical air vent devices that aredesigned to be opened and closed manually must be disabled permanently in the open posi-tion.

Insect screens that do not impede the entry and exit o oodwaters are allowed and do notaect the determination o the net open area. Communities that administer the InternationalBuilding Code (IBC) or the International Residential Code (IRC) should note the require-ment to cover ventilation openings to keep animals and insects rom entering. These codesprovide a list o acceptable covering materials. The commentaries that accompany those codesnote that some covering materials may reduce the gross open area o the vent by as much as50 percent. In areas where oodwaters are expected to carry debris such as grass clippings andleaves, it is notable that screens tend to clog (Figure 15). Local ofcials may determine thatadditional openings are required to increase the likelihood that openings will perorm as ex-pected, even i some become clogged with debris.

Figure 14. Typical standard air vent

aceplate (this example provides 42

square inches o net open area)


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Examples o several commonly used non-engineered openings are described below and shownin Figures 16 through 21:

n Figures 16 and 17 show typical standard air ventilation devices that are intended or instal-lation in crawlspace oundation walls. I installed as ood openings, they must be disabledpermanently in the open position to satisy the requirementor automatic entry and exit o oodwaters (note that the

device shown in Figure 17 is not compliant because it is notdisabled in the open position).

n Figure 18 shows two examples where the builder provideddecorative treatment or open holes; in each case, only thenet open area is counted, and the area covered by the deco-rative treatment is not counted.

n Figure 19 shows a common practice or solid perimeteroundation walls constructed o standard 16 x 8 concretemasonry blocks. I a block is omitted as shown, the result-ing void provides 128 square inches o net open area.

n Figure 20 shows where standard blocks are turned sideways.The voids in the blocks are measured to determine the netopen area.

n Figure 21 shows a oundation in which a hole was createdwhen the concrete was poured; a wood rame covered withscreening is inserted in the hole. The ramed void is mea-sured to determine the net open area.

Figure 15. Typical air

vent clogged by ood

debris

The IRC and IBC (through

reerence to ASCE 24) re-quire that ood openingsare to be not less than 3

inches in any direction inthe plane o the wall. Thisrequirement applies to the

hole in the wall, exclud-ing any device that may be

inserted such as typicaloundation air vent device.

Communities usually re-

quire screens over voids(open holes) that are creat-ed in walls to serve as oodopenings, to limit the entry

o insects and rodents pro-vided the screens do not

impede the inow and out-ow o oodwaters.


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Figure 16. Examples o typical air vents used as ood openings (net open area varies)

Figure 17. Although this standard air vent was intended as ood openings, it is not acceptable because it is not

disabled in the open position and does not allow automatic inow and outow o oodwaters.


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Figure 18. Decorative treatments using fxed louvers and brickwork (count the "net open area" or have

certifed as engineered openings)

Figure 19. Foundation

wall with omitted blocks

as ood openings (insect

screen not visible)


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Figure 20. Concrete block turned sideways (insectscreening shown)

Figure 21. Wood rame with insect screen inserted inopening in poured concrete oundation wall

Engineered Openings

Openings that are designed and certifed by a registered design proessional as meeting theperormance required by the regulations are called engineered openings. This sectiondescribes certifcation and documentation requirements or engineered openings and thespecifc design requirements.

Engineered openings with individual certifcation

For architectural or other reasons, building designers or owners may preer to use uniqueor individually designed openings or devices. In these cases, a registered design proessionalmust submit a certifcation. As a general rule, States require a designer to be licensed to prac-tice in the State in which building is located.

The original certifcation o the engineered openings must include the design proessionalsname, title, address, signature, type o license, license number, the State in which the licensewas issued, and the signature and applied seal o the certiying registered design proessional.The certifcation shall identiy the building in which the engineered openings will be in-stalled. The language o the certifcation shall address the ollowing:

n A statement certiying that the openings are designed to automatically equalize hydrostat-ic ood loads on exterior walls by allowing the automatic entry and exit o oodwaters inaccordance with the Engineered openings, design requirements on page 26,

n Description o the range o ood characteristics tested or computed or which the certif-cation is valid, such as rates o rise and all o oodwaters, and

n Description o the installation requirements or limitations that, i not ollowed, will voidthe certifcation.


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Engineered openings with ICC-ES Evaluation Reports

Engineered openings or devices may be accepted by localofcials as an alternative to non-engineered openings (pre-scriptive) provided the designs are certifed. The certifcationmay take the orm o the individual certifcation described

above, or it can be an Evaluation Report issued by the ICC-ES.The ICC-ES issues such reports or a variety o building prod-ucts, methods, and materials. Evaluation Reports are issuedonly ater the ICC-ES perorms technical evaluations o docu-mentation submitted by a manuacturer, including technicaldesign reports, certifcations, and testing that demonstratecode compliance and perormance.

Evaluation Reports are supported by certifcations that in-clude appropriate language describing perormance o theopenings and the name, title, address, type o license, license

number, the State in which the license was issued, and the sig-nature and seal o the certiying registered design proessional.The specifc provisions that are addressed in the certifcationmust include:

n A statement certiying that the openings are designed to automatically equalize hydrostat-ic ood loads on exterior walls by allowing the automatic entry and exit o oodwaters inaccordance with the Engineered openings, design requirements below,

n Description o the range o ood characteristics tested or computed or which the certif-cation is valid, such as rates o rise and all o oodwaters, and

n Description o the installation requirements or limitations that, i not ollowed, will voidthe certifcation.

Documentation o engineered openings or compliance

An important part o the evidence necessary to document compliance is the certifcation oengineered openings or the Evaluation Report. A copy o the individual certifcation or theEvaluation Report is required to be kept in the communitys permanent permit fles, alongwith inspection reports. The documentation can be submitted as part o the permit applica-tion and design drawings, or submitted separately. Owners should retain the certifcation or acopy o the Evaluation Report to submit along with applications or NFIP ood insurance.

Documentation o engineered openings or ood insurance

Insurance agents will request that property owners provide documentation as part o appli-cations or NFIP ood insurance. The documentation should be attached to the ElevationCertifcate. The ollowing are acceptable orms o documentation:

n For engineered openings with individual certifcation, the certifcation described abovethat is signed and sealed by a registered design proessional who is licensed in the Statewhere the building in which the engineered openings are used is located; or

ICC-ES has issued

Acceptance Criteria orAutomatic Foundation Flood

Vents(AC364) or one type

o engineered opening. TheICC-ES will develop ac-ceptance criteria or other

types, upon request.

Local ofcials in communi-ties that do not administer

the International CodeSeries determine whether

to accept building prod-ucts that have received

Evaluation Reports issuedby the ICC-ES.


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n For engineered openings with ICC-ES Evaluation Reports, a copy o the Evaluation Reportthat documents that the engineered openings meet the perormance requirements o theNFIP and the building code, and that specifes the number o such openings that are re-quired or a specifed square ootage o enclosed area below the BFE; or

n For engineered openings with ICC-ES Evaluation Reports, a letter or other written evi-

dence rom the local ofcial that use o engineered openings in a specifc building isacceptable.

Engineered openings, design requirements

The American Society o Civil Engineers (ASCE) developed the standardFlood Resistant Designand Construction(ASCE 24). This standard applies to buildings and site developments pro-posed in ood hazard areas; it is reerenced by the International Building Code. ASCE 24 Section2.6.2.2 contains installation and design criteria or engineered openings. ASCE 24 providesthe equation below to determine the total net area o engineered openings that are installedin oundation walls or enclosure walls. The equation includes a coefcient that corresponds

to a actor o saety o 5, which is consistent with design practices related to protection o lieand property. This actor o saety also helps to account or the likelihood that insect screensmay clog with ood-borne debris. The ASCE 24 commentary provides additional backgroundon the derivation o the equation.

As with non-engineered openings, engineered openings must be designed to allow automaticentry and exit o oodwaters.

Three design and perormance criteria or engineered openings are specifed in ASCE 24 butare not explicitly identifed in the NFIP regulations:

n Engineered openings are to perorm such that dierence between the exterior and inte-

rior water levels shall not exceed 1 oot during base ood conditions.

n Engineered openings are to be not less than 3 inches in any direction in the plane o thewall. This requirement applies to the hole in the wall, excluding any screen, grate, grille,louvers, or devices that may be placed in or over the opening.

n In the absence o reliable data on the rates o rise and all, engineered openings are to bedesigned based on the assumption that the minimum rate o rise and all will be 5 eet perhour. Where data or analyses indicate more rapid rates o rise and all, the required num-ber o openings is to be increased to account or those dierent conditions. The numberor size o the openings may be decreased i data or analyses indicate rates o rise and allare less than 5 eet per hour.


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From ASCE 24, the equation to determine area o engineered openings:

Ao

= 0.033 [1/c] R Ae

Where: Ao

= total net area o openings required (in)

0.033 = coefcient corresponding to a actor o saety o 5.0 (in hr/t)

c = opening coefcient (non-dimensional; see ASCE 24,Table 2-2)

R = worst case rate o rise and all (t/hr)

Ae

= total enclosed area (t)

[ASCE 24] Table 2-2

Flood Opening Coefcient o Discharge

Opening Shape and Condition c

circular, unobstructed during design ood 0.60

rectangular, long axis horizontal, short axisvertical, unobstructed during design ood

0.40a

square, unobstructed during design ood 0.35

rectangular, short axis horizontal, long axisvertical, unobstructed during design ood

0.25b

other shapes, unobstructed during design ood 0.30

Notes:

a. When the horizontal dimension is twice or more the vertical dimension, use0.4; as the dimensions approach a square, interpolate rom 0.4 to 0.35.

b. When the horizontal dimension is hal or less the vertical dimension, use 0.25;as the dimensions approach a square, interpolate rom 0.25 to 0.35.

Used with permission rom ASCE.


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The NFIP

The U.S. Congress established the NFIP with the passage o the National Flood InsuranceAct o 1968. The NFIP is a Federal program enabling property owners in participating com-munities to purchase insurance as protection against ood losses, in exchange or State and

community oodplain management regulations that reduce uture ood damages. Participa-tion in the NFIP is based on an agreement between communities and the Federal Government.I a community adopts and enorces adequate oodplain management regulations, FEMA willmake ood insurance available within the community.

Title 44 o the U.S Code o Federal Regulations contains the NFIP criteria or oodplain man-agement, including design and construction standards or new and substantially improvedbuildings located in SFHAs identifed on the NFIPs Flood Insurance Rate Maps. FEMA en-courages communities to adopt oodplain management regulations that exceed the NFIPcriteria. As an insurance alternative to disaster assistance, the NFIP reduces the escalatingcosts o repairing damage to buildings and their contents caused by oods.

NFIP Technical Bulletins

This is one o a series o Technical Bulletins that FEMA has produced to provide guidanceconcerning the building perormance requirements o the NFIP. These requirements are con-tained in Title 44 o the U.S. Code o Federal Regulations at Section 60.3. The bulletins areintended or use by State and local ofcials responsible or interpreting and enorcing the re-quirements in their oodplain management regulations and building codes, and by memberso the development community, such as design proessionals and builders. New bulletins, as

well as updates o existing bulletins, are issued periodically, as necessary. The bulletins do notcreate regulations; rather, they provide specifc guidance or complying with the requirementso existing NFIP regulations. Users o the Technical Bulletins who need additional guidanceshould contact their NFIP State Coordinator or the appropriate FEMA regional ofce. TheUsers Guide to Technical Bulletins(http://www.ema.gov/pd/fnal/guide01.pd) lists the bul-letins issued to date.

Ordering Technical Bulletins

The quickest and easiest way to acquire copies o FEMAs Technical Bulletins is to down-

load them rom the FEMA website (http://www.ema.gov/plan/prevent/oodplain/techbul.shtm).

Technical Bulletins also may be ordered ree o charge rom the FEMA Publications Ware-house by calling 1-800-480-2520, or by axing a request to 301-362-5355, Monday throughFriday between 8 a.m. and 5 p.m. EST. Please provide the FEMA publication number, title,and quantity o each publication requested, along with your name, address, zip code, and day-time telephone number. Written requests may be also be submitted by mail to the ollowingaddress:


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FEMA PublicationsP.O. Box 2012Jessup, MD 20794

Further InormationThe ollowing sources provide urther inormation concerning openings in oundation wallsand walls o enclosures.

American Society o Civil Engineers, Structural Engineering Institute. 2005.Flood Resistant De-sign and Construction, ASCE/SEI 24-05.

American Society o Civil Engineers, Structural Engineering Institute. 2005. Minimum DesignLoads or Buildings and Other Structures, ASCE/SEI 7-05.

FEMA. 1991. Answers to Questions About Substantially Damaged Buildings, FEMA 213.

FEMA. 2000. Coastal Construction Manual, FEMA 55CD (3rd edition).

FEMA. 2004. Floodplain Management Bulletin: Elevation Certifcate, FEMA 467-1 (http://www.ema.gov/pd/fma/ema467-6-10-04.pd).

FEMA. 2005. Home Builders Guide to Coastal Construction: Technical Fact Sheet Series, FEMA 499.

FEMA. 2006. Elevation Certifcate(FEMA Form 81-31, http://www.ema.gov/pd/nfp/elvcert.shtm).

ICC Evaluation Service, Inc. 2007. Acceptance Criteria or Automatic Foundation Flood Vents(AC364,http://www.icc-es.org/criteria/pd_fles/ac364.pd).

International Code Council, Inc. 2006. International Building Code, IBC 2006.

International Code Council, Inc. 2006. International Residential Code, IRC 2006.

National Fire Protection Association. 2005. Model Manuactured Home Installation Standard,NFPA 225.

National Fire Protection Association. 2006. Building Construction and Saety Code, NFPA 5000.


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Glossary

Accessory structure A structure that is on the same parcel o property as a principal struc-ture, the use o which is incidental to the use o the principal structure.

Base ood The ood having a 1-percent chance o being equaled or exceeded in any givenyear, commonly reerred to as the 100-year ood. The base ood is the national standardused by the NFIP and all Federal agencies or the purposes o requiring the purchase o oodinsurance and regulating new development.

Base ood elevation (BFE) The height o the base (1-percent annual chance or 100-year)ood in relation to a specifed datum, usually the National Geodetic Vertical Datum o 1929(NGVD), or the North American Vertical Datum o 1988 (NAVD).

Basement Any area o a building having its oor subgrade (below ground level) on allsides.

Elevation certifcate A orm developed by FEMA to collect surveyed elevations and other A orm developed by FEMA to collect surveyed elevations and otherA orm developed by FEMA to collect surveyed elevations and otherinormation about a building that is necessary to obtain ood insurance.

Enclosure or enclosed area Areas created by a crawlspace or solid walls that ully enclose Areas created by a crawlspace or solid walls that ully encloseAreas created by a crawlspace or solid walls that ully encloseareas below the BFE.

Federal Emergency Management Agency (FEMA) The Federal agency that, in addition toThe Federal agency that, in addition tocarrying out other activities, administers the National Flood Insurance Program.

Flood Insurance Rate Map (FIRM) The ofcial map o a community on which FEMA hasThe ofcial map o a community on which FEMA has

delineated both the special ood hazard areas (SFHAs) and the risk premium zones applica-ble to the community.

Hydrodynamic load The load imposed on an immersed object, such as a oundation element The load imposed on an immersed object, such as a oundation elementThe load imposed on an immersed object, such as a oundation elementor enclosure wall, by water owing against and around it. The magnitude o the hydrodynam-ic load varies as a unction o velocity and other actors.

Hydrostatic load The load imposed on an immersed object such as an enclosure wall, by The load imposed on an immersed object such as an enclosure wall, byThe load imposed on an immersed object such as an enclosure wall, bystanding or slowly moving water. The magnitude o the hydrostatic load increases linearly withwater depth.

Lowest oor The lowest oor o the lowest enclosed area o a building, including a basement. The lowest oor o the lowest enclosed area o a building, including a basement.The lowest oor o the lowest enclosed area o a building, including a basement.Any NFIP-compliant unfnished or ood-resistant enclosure usable used solely or parking ovehicles, building access, or storage (in an area other than a basement) is not considered abuildings lowest oor, provided the enclosure does not render the structure in violation othe applicable design requirements o the NFIP.

Mitigation Directorate The component o FEMA directly responsible or administering theood hazard identifcation and oodplain management aspects o the NFIP.


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Net open area The permanently open area o a non-engineered opening intended to pro-The permanently open area o a non-engineered opening intended to pro-vide automatic entry and exit o oodwaters.

Opening, engineered An engineered opening is an opening that is designed and certifed An engineered opening is an opening that is designed and certifedAn engineered opening is an opening that is designed and certifedby a registered design proessional as meeting certain perormance characteristics related to

providing automatic entry and exit o oodwaters; the certifcation requirement may be satis-fed by an individual certifcation or issuance o an Evaluation Report by the ICC EvaluationService, Inc.

Opening, non-engineered A non-engineered opening is an opening that is used to meet A non-engineered opening is an opening that is used to meetA non-engineered opening is an opening that is used to meetthe NFIPs prescriptive requirement o 1 square inch o net open area or every square oot oenclosed area.

Registered Design Proessional An individual who is registered or licensed to practice theirAn individual who is registered or licensed to practice theirrespective design proession as defned by the statutory requirements o the proessional reg-istration laws o the State or jurisdiction in which the project is to be constructed.

Special Flood Hazard Area (SFHA) An area delineated on a FIRM as being subject to in-An area delineated on a FIRM as being subject to in-undation by the base ood and designated as Zone A, AE, A1-A30, AR, AO, AH, A99, V, VE,or V1-V30.

Substantial damage Damage o any origin sustained by a structure whereby the cost o re- Damage o any origin sustained by a structure whereby the cost o re-Damage o any origin sustained by a structure whereby the cost o re-storing the structure to its beore-damaged condition would equal or exceed 50 percent othe market value o the structure beore the damage occurred. Structures that are determinedto be substantially damaged are considered to be substantial improvements, regardless o theactual repair work perormed.

Substantial improvement Any reconstruction, rehabilitation, addition, or other improve-Any reconstruction, rehabilitation, addition, or other improve-ment o a structure, the cost o which equals or exceeds 50 percent o the market value othe structure (or smaller percentage i established by the community) beore the start oconstruction o the improvement. This term includes structures that have incurred substan-tial damage, regardless o the actual repair work perormed.


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FEMA Hydro Static Relief Info.

Documents

Transcript of FEMA Hydro Static Relief Info.