SECTION 1203 VENTILATION
1203.2 Attic spaces.
Enclosed attics and enclosed rafter spaces formed where ceilings
are applied directly to the underside of roof framing members
shall have cross ventilation for each separate space by ventilating
openings protected against the entrance of rain and snow.
Blocking and bridging shall be arranged so as not to interfere
with the movement of air. A minimum of 1 inch (25 mm) of airspace
shall be provided between the insulation and the roof sheathing.
The net free ventilating area shall not be less than 1/150
of the area of the space ventilated, with 50 percent of the
required ventilating area provided by ventilators located
in the upper portion of the space to be ventilated at least
3 feet (914 mm) above eave or cornice vents with the balance
of the required ventilation provided by eave or cornice vents.
Exception: The minimum
required net free ventilating area shall be 1/300
of the area of the space ventilated, provided a vapor retarder
having a transmission rate not exceeding 1 perm in accordance
with ASTM E 96 is installed on the warm side of the attic
insulation and provided 50 percent of the required ventilating
area provided by ventilators located in the upper portion
of the space to be ventilated at least 3 feet (914 mm) above
eave or cornice vents, with the balance of the required ventilation
provided by eave or cornice vents.
1203.2.1 Openings into attic.
Exterior openings into the attic space of any building intended
for human occupancy shall be covered with corrosion-resistant
wire cloth screening, hardware cloth, perforated vinyl or
similar material that will prevent the entry of birds, squirrels,
rodents, snakes and other similar creatures. The openings
therein shall be a minimum of 1/8 inch
(3.2 mm) and shall not exceed 1/4 inch
(6.4 mm). Where combustion air is obtained from an attic area,
it shall be in accordance with Chapter 7 of the International
Mechanical Code.
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