Current through Register 1531, September 27, 2024
The space between the bottom of the floor joists and the
earth under any building except spaces occupied by basements or cellars shall
be provided with ventilation openings through foundation walls or
exterior walls. Such openings shall be placed so as to provide
cross ventilation of the under-floor space.
1203.3.1
Openings for under-floor
ventilation. The minimum net area of ventilation openings shall not be
less than 1 square foot for each 150 square feet (0.67
m2 for each 100 m2) of
crawl-space area. Ventilation openings shall be covered for their height and
width with any of the following materials, provided that the least dimension of
the covering shall not exceed
1/4 inch (6 mm):
1. Perforated sheet metal plates not less
than 0.070 inch (1.8 mm) thick.
2.
Expanded sheet metal plates not less than 0.047 inch (1.2 mm) thick.
3. Cast-iron grilles or gratings.
4. Extruded load-bearing vents.
5. Hardware cloth of 0.035 inch (0.89 mm)
wire or heavier.
6.
Corrosion-resistant wire mesh, with the least dimension not exceeding
1/8 inch (3.2 mm).
1203.3.2
Exceptions.
The following are exceptions to Sections 1203.3 and 1203.3.1:
1. Where warranted by climatic conditions,
ventilation openings to the outdoors are not required if ventilation openings
to the interior are provided.
2.
The total area of ventilation openings is permitted to be reduced to
1/1,500 of the under-floor
area where the ground surface is covered with a Class I vapor retarder material
and the required openings are placed so as to provide cross ventilation of the
space. The installation of operable louvers shall not be prohibited.
3. Ventilation openings are not required
where continuously operated mechanical ventilation is provided at a rate of 1.0
cubic foot per minute (cfm) for each 50 square feet (1.02 L/s for each 10
m2) of crawl space floor area and the ground surface
is covered with a Class I vapor retarder.
4. Ventilation openings are not required when
the ground surface is covered with a Class I vapor retarder, the perimeter
walls are insulated and the space is conditioned in accordance with the
International Energy Conservation Code.
5. For buildings in flood hazard areas as
established in Section 1612.3, the openings for under-floor ventilation shall
be deemed as meeting the flood opening requirements of ASCE 24 provided that
the ventilation openings are designed and installed in accordance with ASCE
24.
