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Frequently Asked Questions About FEMA Requirements

Do I need certification that my flood vents have engineered openings?
What information needs to be included on the certificate?
Do all flood vents need to be ICC-ES evaluated?
Does a flood vent need to have a 3" opening as required by FEMA?
Can a flood vent have a cover over it or a screen in the opening?
What are the FEMA/NFIP requirements for installation of flood vents?
What isn't allowed by FEMA?

Do I need certification that my flood vents have engineered openings?

YES, it is a requirement that you have an engineered certificate from the manufacturer of the vent in order to be able to use the engineered calculations to determine how many vents you will require.

This certificate must be from the state in which your building is located, unless the vent is ICC-ES certified and has an ICC-ES evaluation report. If the vent has neither an engineered certificate from the state in which your building is located or does not have an ICC-ES evaluation report than you may not use the engineered calculations for the vent to determine how many vents you will require. You would then have to use the ACTUAL net free air of the vent to determine how many vents you will require. This would require far more vents to meet the requirements.

The original certification statement must include:

The design professional’s name and title, address, type of license, license number and the state in which the license was issued along with the signature of the design professional and an applied seal of the certifying registered design professional.

In addition, the certification has to identify the building in which the engineered opening will be installed and it needs to 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.
  • Description of the range of flood characteristics tested or computed for which the certification is valid, such as rates of rise and fall of floodwaters.
  • Description of the installation requirements or limitations that, if not followed, will void the certification.

This data is a certification as having been designed to provide automatic equalization of hydrostatic flood forces by allowing for the entry and exit of flood waters.

Do all flood vents need to be ICC-ES evaluated?

No. This is a test for flood vents that automatically allow water to enter and exit a structure during a flood event to be sure that the vent will open and close as required.

ICC-ES evaluation need not be provided for engineered openings as long as an engineered certificate is provided. The certificate MUST be issued by a design professional within the same state as the building is located. Certificates from another state are not acceptable.

Does a flood vent need to have a 3" opening as required by FEMA?

NO. The requirement refers to only the hole in the wall that the flood vent is to be installed within, excluding any screen, grate, louver or devices that may be placed in or over the opening. The hole must be not less than 3 inches in any direction in the plane of the wall.

Can a flood vent have a cover over it or a screen in the opening?

Openings may be equipped with screens, louvers, valves, or other coverings or devices provided that they permit the automatic entry and exit of floodwaters.

A vent cover that impedes the automatic entry and exit of floodwaters is not permitted. This would pertain to, for example, a cover over the face of the vent for the winter that would not allow for the automatic entry and exit of floodwaters. If this cover needs to be manually removed before a flood event to allow for the automatic entry and exit of floodwaters, it’s not permitted.

Screens are permitted as they do allow the automatic entry and exit of floodwaters.

What are the requirements by FEMA/NFIP for installation of flood vents?

The following requirements for installation apply regardless of whether engineered openings or non-engineered openings are used to satisfy the NFIP requirements. You’ll find the technical information below, but simply put, FEMA/NFIP requirements include:

  • A minimum of one square inch of net open area for each square foot of enclosed area for non-engineered openings OR a minimum of ONE engineered inch for each square foot of enclosed area for an engineered opening.
  • A minimum of two vents per enclosed area, and each must be on at least two different sides of the exterior walls.
  • The bottom of the flood vent opening must not be higher than 12 inches above the grade.
  • An engineered certificate from the state in which the building is located is required for all engineered openings without ICC-ES certification.

Openings
Each enclosed area must have a minimum of two openings; if there are multiple enclosed areas, each area must have openings in its exterior walls, the openings should be installed on at least two sides of each enclosed area to decrease the chances that all openings could be blocked with floating debris and to allow for more even filling by floodwater and draining of the enclosed area.

It is recommended that openings be reasonably distributed around the perimeter of the enclosed area unless there is clear justifi­cation for putting all openings on just one or two sides (such as in townhouses or buildings set into sloping sites).

Non-engineered openings are openings that are used to satisfy the prescriptive requirement that calls for one square inch of net open area for each square foot of enclosed area.

Engineered openings are openings that have been designed and certified by a design professional; engineered openings require fewer vents to satisfy the requirements of the NFIP and FEMA.

Number of openings
ASCE 24 provides an equation to determine the total net area of engineered openings that are installed in foundation walls or enclosure walls. The equation includes a coefficient that corresponds to a factor of safety of 5, which is consistent with design practices related to protection of life and property. This factor of safety also helps to account for the likelihood that insect screens may clog with flood-borne debris. The ASCE 24 commentary provides additional background on the derivation of the equation.

The bottom of each opening must be no more than 12 inches higher above the interior or exterior grade immediately under the opening, and a minimum of two vents per enclosed area, on at least two different sides of the exterior wall must be provided.

Screens, grates, etc.
Any screens, grates, grilles, fixed louvers, or other covers or devices must not block or im­pede the automatic flow of floodwaters into and out of the enclosed area.

What isn't allowed by FEMA?

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

  • Standard foundation air ventilation devices that are closed manually because they do not allow for the automatic entry and exit of floodwaters unless they’re permanently dis­abled in the open position.
  • Standard foundation air ventilation devices that have detachable solid covers that are in­tended to be manually installed over the opening in cold weather, because they do not allow for the automatic entry and exit of floodwaters when the cover is in place.
  • Standard foundation air ventilation devices that are designed to open and close based on temperature (unless they also are designed to allow for the automatic entry and exit of floodwaters).
  • Windows below the BFE because the automatic entry and exit of floodwaters cannot be satisfied by the expectation that windows will break under rising floodwaters.
  • Garage doors without openings installed in them, because human intervention is required to open the doors when flooding is expected. Gaps between the garage door and the doorjamb or walls do not count towards the net open area requirement.
  • Standard exterior doors without openings installed in them.

Source:
FEMA Technical Bulletin 1 / August 2008 (TB-1/2008)

 

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