Flood opening
Encyclopedia
A flood opening or flood vent is an orifice in an enclosed structure intended to allow the free passage of water between the interior and exterior.
, flood openings are used to provide for the automatic equalization of hydrostatic pressure on either side of a wall. Building codes usually require the installation of flood openings in the walls of structures located in FEMA-recognized A-type flood zones. Various agencies in the United States define necessary characteristics for flood openings.
requirements apply to any structure that is not dry flood-proofed and which is in the mapped flood zone. It calls for openings in load-bearing foundation walls located below the mapped flood elevation. Where non-engineered openings are used, each opening must be at least three inches in diameter, and have no screen or other cover that interferes with the transition of water between interior and exterior. The total net open area of all flood openings in the structure must be equal to or greater than one square inch, per square foot of footprint of the enclosed area—though no fewer than two openings, total, which must be located on different walls. Openings must be placed such that the bottom of each opening is no more than one foot above the adjacent ground level.
In lieu of these requirements, engineered openings must conform to a performance standard: during a flood with a rate of rise/fall of five feet per hour, the difference between interior and exterior flood water levels in an enclosure using the engineered openings must not be greater than one foot.
refers to the American Society of Civil Engineer requirements for both non-engineered and engineered flood openings.
does not have the authority over the building code, it maintains crucial influence over flood opening standards through its administration of the National Flood Insurance Program
, or NFIP. By controlling the de facto standards for nearly all flood insurance
in the United States, the NFIP exerts exceptional authority over many aspects of floodplain construction. The FEMA (and, thus, NFIP) requirements for non-engineered openings are largely in accord with those of the American Society of Civil Engineers. They differ in that FEMA requires the placement of openings such that the bottom of each opening is no more than one foot above the higher of the adjacent ground level, or the interior foundation slab height.
For engineered openings, FEMA offers two subclassifications: individual certification openings, and openings with ICC-ES Evaluation Reports. Individual certification openings are offered for use when, "[f]or architectural or other reasons, building designers or owners may prefer to use unique or individually designed openings or devices". In such cases, an architect
or engineer
may provide certification including the professional's signature and applied seal. The certification must include a "statement certifying that the openings are designed to automatically equalize hydrostatic flood loads on exterior walls by allowing the automatic entry and exit of floodwaters in accordance with the...design requirements"; "[d]escription of the range of flood characteristics tested or computed for which the certification is valid, such as rates of rise and fall of floodwaters"; and "[d]escription of the installation requirements and limitations that, if not followed, will void the certification". The nature of the "live seal" requirement means that each structure containing an individual certification opening must have a separate certification, even if the opening is identical to that used in another structure.
The alternative subclassification is an opening that carries certification through the International Code Council Evaluation Service., According to FEMA, "Evaluation Reports are issued only after the ICC-ES performs technical evaluations of documentation submitted by a manufacturer, including technical design reports, certifications, and testing that demonstrate code compliance and performance." The report must include a statement concerning the purpose of the opening tested; a description of the characteristics tested; and a description of installation requirements. FEMA allows a copy of the report to be used as a blanket certification of any project including an ICC-ES certified opening, in contrast to the requirements of an individual certification opening.
s per minute
flooding, at a minimum of five foot per hour rate of rise. Additionally, water levels on the testing tank's "interior" and "exterior" portions must at no point differ more than one foot. To gauge performance against waterborne debris
, leaves and grass clippings are added to both chambers of the tank.
Flood Openings in the United States
In the United StatesUnited States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
, flood openings are used to provide for the automatic equalization of hydrostatic pressure on either side of a wall. Building codes usually require the installation of flood openings in the walls of structures located in FEMA-recognized A-type flood zones. Various agencies in the United States define necessary characteristics for flood openings.
Engineered vs. Non-Engineered Openings
Most regulatory authorities in the United States that offer requirements for flood openings define two major classes of opening: engineered, and non-engineered. The requirements for non-engineered openings are typically stricter, defining necessary characteristics for aspects ranging from overall size of each opening, to allowable screening or other coverage options, to number and placement of openings. Engineered openings receive special dispensation to ignore many of these requirements, depending on the particular regulatory authority. To qualify as an engineered opening, testing and/or certification by a qualified agency (varying from regulator to regulator, and indicated below where appropriate) is required.American Society of Civil Engineers Definition
The ASCEAmerican Society of Civil Engineers
The American Society of Civil Engineers is a professional body founded in 1852 to represent members of the civil engineering profession worldwide. It is the oldest national engineering society in the United States. ASCE's vision is to have engineers positioned as global leaders who strive toward...
requirements apply to any structure that is not dry flood-proofed and which is in the mapped flood zone. It calls for openings in load-bearing foundation walls located below the mapped flood elevation. Where non-engineered openings are used, each opening must be at least three inches in diameter, and have no screen or other cover that interferes with the transition of water between interior and exterior. The total net open area of all flood openings in the structure must be equal to or greater than one square inch, per square foot of footprint of the enclosed area—though no fewer than two openings, total, which must be located on different walls. Openings must be placed such that the bottom of each opening is no more than one foot above the adjacent ground level.
In lieu of these requirements, engineered openings must conform to a performance standard: during a flood with a rate of rise/fall of five feet per hour, the difference between interior and exterior flood water levels in an enclosure using the engineered openings must not be greater than one foot.
International Building Code (IBC)
The International Building CodeInternational Building Code
The International Building Code is a model building code developed by the International Code Council . It has been adopted throughout most of the United States.-History:...
refers to the American Society of Civil Engineer requirements for both non-engineered and engineered flood openings.
International Residential Code (IRC)
The International Residential Code requirements vary mildly from revision to revision, but require that entry and exit of floodwater be provided for in accordance with the requirements of the ASCE. These requirements apply for both non-engineered and engineered flood openings.FEMA
While the Federal Emergency Management AgencyFederal Emergency Management Agency
The Federal Emergency Management Agency is an agency of the United States Department of Homeland Security, initially created by Presidential Reorganization Plan No. 1 of 1978 and implemented by two Executive Orders...
does not have the authority over the building code, it maintains crucial influence over flood opening standards through its administration of the National Flood Insurance Program
National Flood Insurance Program
The National Flood Insurance Program is a program created by the Congress of the United States in 1968 through the National Flood Insurance Act of 1968 . The program enables property owners in participating communities to purchase insurance protection from the government against losses from flooding...
, or NFIP. By controlling the de facto standards for nearly all flood insurance
Flood insurance
Flood insurance denotes the specific insurance coverage against property loss from flooding. To determine risk factors for specific properties, insurers will often refer to topographical maps that denote lowlands, floodplains and floodways that are susceptible to flooding.-Hidden floods:Nationwide,...
in the United States, the NFIP exerts exceptional authority over many aspects of floodplain construction. The FEMA (and, thus, NFIP) requirements for non-engineered openings are largely in accord with those of the American Society of Civil Engineers. They differ in that FEMA requires the placement of openings such that the bottom of each opening is no more than one foot above the higher of the adjacent ground level, or the interior foundation slab height.
For engineered openings, FEMA offers two subclassifications: individual certification openings, and openings with ICC-ES Evaluation Reports. Individual certification openings are offered for use when, "[f]or architectural or other reasons, building designers or owners may prefer to use unique or individually designed openings or devices". In such cases, an architect
Architect
An architect is a person trained in the planning, design and oversight of the construction of buildings. To practice architecture means to offer or render services in connection with the design and construction of a building, or group of buildings and the space within the site surrounding the...
or engineer
Engineer
An engineer is a professional practitioner of engineering, concerned with applying scientific knowledge, mathematics and ingenuity to develop solutions for technical problems. Engineers design materials, structures, machines and systems while considering the limitations imposed by practicality,...
may provide certification including the professional's signature and applied seal. The certification must include a "statement certifying that the openings are designed to automatically equalize hydrostatic flood loads on exterior walls by allowing the automatic entry and exit of floodwaters in accordance with the...design requirements"; "[d]escription of the range of flood characteristics tested or computed for which the certification is valid, such as rates of rise and fall of floodwaters"; and "[d]escription of the installation requirements and limitations that, if not followed, will void the certification". The nature of the "live seal" requirement means that each structure containing an individual certification opening must have a separate certification, even if the opening is identical to that used in another structure.
The alternative subclassification is an opening that carries certification through the International Code Council Evaluation Service., According to FEMA, "Evaluation Reports are issued only after the ICC-ES performs technical evaluations of documentation submitted by a manufacturer, including technical design reports, certifications, and testing that demonstrate code compliance and performance." The report must include a statement concerning the purpose of the opening tested; a description of the characteristics tested; and a description of installation requirements. FEMA allows a copy of the report to be used as a blanket certification of any project including an ICC-ES certified opening, in contrast to the requirements of an individual certification opening.
AC364-1006-R1
AC364-1006-R1 documents the ICC-ES's testing standards for flood openings, including specifications for a dual-chambered testing tank. While the requirements for the opening itself are based on ASCE 24, the substance of the test adds new layers of performance expectation. Under these requirements, the opening must activate before water level is one foot above the bottom of the opening, under conditions of 50 and 300 gallonGallon
The gallon is a measure of volume. Historically it has had many different definitions, but there are three definitions in current use: the imperial gallon which is used in the United Kingdom and semi-officially within Canada, the United States liquid gallon and the lesser used United States dry...
s per minute
Minute
A minute is a unit of measurement of time or of angle. The minute is a unit of time equal to 1/60th of an hour or 60 seconds. In the UTC time scale, a minute on rare occasions has 59 or 61 seconds; see leap second. The minute is not an SI unit; however, it is accepted for use with SI units...
flooding, at a minimum of five foot per hour rate of rise. Additionally, water levels on the testing tank's "interior" and "exterior" portions must at no point differ more than one foot. To gauge performance against waterborne debris
Debris
Debris is rubble, wreckage, ruins, litter and discarded garbage/refuse/trash, scattered remains of something destroyed, or, in geology, large rock fragments left by a melting glacier etc. The singular form of debris is debris...
, leaves and grass clippings are added to both chambers of the tank.