7) How should the total area of permanent openings for section C3.i) be
calculated if the openings include some type of cover?
Buildings constructed on extended foundation walls or that have other enclosures below the Base
Flood Elevation in A Zones are subject to flood forces that include hydrostatic pressure of
floodwaters against the foundation or enclosure walls. If the walls are not designed to withstand
hydrostatic pressure, they can be weakened or can fail causing damages to the building. The NFIP
Regulations at 44 CFR 60.3(c)(5) require that foundation and enclosure walls of buildings
constructed in A Zones contain openings (flood vents) that will permit the automatic entry and exit
of floodwaters. These openings allow floodwaters to reach equal levels on both sides of the walls
and thereby lessen the potential for damage from hydrostatic pressure. Under the NFIP, the
following requirements must be met for all new or substantially improved A Zone buildings that
have enclosed areas below the Base Flood Elevation:
• There must be a minimum of two openings and the openings should be on different sides of
each enclosed area. If a building has more than one enclosed area, each area must have
openings on exterior walls to allow floodwater to directly enter.
• The total net area of all openings must be at least 1 square inch for each 1 square foot of
• The bottom of each opening can be no more than 1 foot above the adjacent grade.
In situations where it is not feasible or desirable to meet the openings criteria stated above, a design
professional (registered architect or engineer) may design and certify the openings. See Technical
Bulletin 1-93 on Openings in Foundation Walls for Buildings Located in Special Flood Hazard
Areas (FIA-TB-1) for additional guidance on the openings requirement. In all cases, any grates,
louvers, grills, bars, or other opening covers must not block or impede the automatic flow of
floodwaters into and out of the enclosed area.
Figure 2. Limited Access to Crawl Space
Letters equate to items
in Section C3. of the
a) Top of bottom floor
b) Top of next higher
f) Lowest adjacent
g) Highest adjacent
h) No. of permanent
i) Total area of all
in square inches.
National Flood Insurance Program Floodplain Management Bulletin
Page 10 of 20
Item C3.h) of the Elevation Certificate asks for the number of permanent openings in the walls
supporting the building that are no higher than 1 foot above the adjacent grade and item C3.i) asks
for the total area of all such openings in square inches. If there are no permanent openings within 1
foot above the adjacent grade, “0” (zero) should be entered in items C3.h) and i). Also, the surveyor
should note in the Comments section whether the openings are in the foundation walls of the
building and/or in the walls of any attached garage.
When there are grates, louvers, grills, or other opening covers as indicated in Figure 3, the surveyor
can estimate the net open area in the flood vent (total area of all permanent openings in square
inches). If the size of the openings, excluding any grates, louvers, grills, or other covers, cannot be
estimated, the surveyor can measure the size of the opening, without consideration to the existence
of any covers, and indicate in the comment section the type of opening cover that exists. It is the
community’s responsibility and not the surveyor’s to determine whether the size, number, and
location of the openings meet the requirements of the community’s floodplain management