International Building Code Section 1203


International Building Code 1203.1

General. Buildings shall be provided with natural ventilation
in accordance with Section 1203.4, or mechanical ventilation
in accordance with the International Mechanical Code.

International Building Code 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.Aminimum
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.

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.

International Building Code 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.

International Building Code 1203.3

Under-floor ventilation. The space between the bottom
of the floor joists and the earth under any building except
spaces occupied by a basement or cellar 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.

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).

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 treated with an approved 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
2006 INTERNATIONAL BUILDING CODE 249
floor area and the ground surface is covered with an
approved vapor retarder.
4. Ventilation openings are not required when the
ground surface is covered with an approved 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.

International Building Code 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).

International Building Code 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 treated with an approved 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
2006 INTERNATIONAL BUILDING CODE 249
floor area and the ground surface is covered with an
approved vapor retarder.
4. Ventilation openings are not required when the
ground surface is covered with an approved 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.

International Building Code 1203.4

Natural ventilation. Natural ventilation of an occupied
space shall be through windows, doors, louvers or other
openings to the outdoors. The operating mechanism for such
openings shall be provided with ready access so that the openings
are readily controllable by the building occupants.

Ventilation area required. The minimum
openable area to the outdoors shall be 4 percent of the floor
area being ventilated.

Adjoining spaces. Where rooms and spaces
without openings to the outdoors are ventilated through
an adjoining room, the opening to the adjoining room
shall be unobstructed and shall have an area of not less
than 8 percent of the floor area of the interior room or
space, but not less than 25 square feet (2.3m2). The minimum
openable area to the outdoors shall be based on the
total floor area being ventilated.
Exception: Exterior openings required for ventilation
shall be permitted to open into a thermally isolated
sunroom addition or patio cover provided that
the openable area between the sunroom addition or
patio cover and the interior room shall have an area of
not less than 8 percent of the floor area of the interior
room or space, but not less than 20 square feet (1.86
m2). The minimum openable area to the outdoors
shall be based on the total floor area being ventilated.

Openings below grade. Where openings
below grade provide required natural ventilation, the
outside horizontal clear space measured perpendicular to
the opening shall be one and one-half times the depth of
the opening. The depth of the opening shall be measured
from the average adjoining ground level to the bottom of
the opening.

Contaminants exhausted. Contaminant sources
in naturally ventilated spaces shall be removed in accordance
with the International Mechanical Code and the
International Fire Code.

Bathrooms. Rooms containing bathtubs,
showers, spas and similar bathing fixtures shall be
mechanically ventilated in accordance with the International
Mechanical Code.

Openings on yards or courts. Where natural ventilation
is to be provided by openings onto yards or courts,
such yards or courts shall comply with Section 1206.

International Building Code 1203.4.1

Ventilation area required. The minimum
openable area to the outdoors shall be 4 percent of the floor
area being ventilated.

Adjoining spaces. Where rooms and spaces
without openings to the outdoors are ventilated through
an adjoining room, the opening to the adjoining room
shall be unobstructed and shall have an area of not less
than 8 percent of the floor area of the interior room or
space, but not less than 25 square feet (2.3m2). The minimum
openable area to the outdoors shall be based on the
total floor area being ventilated.
Exception: Exterior openings required for ventilation
shall be permitted to open into a thermally isolated
sunroom addition or patio cover provided that
the openable area between the sunroom addition or
patio cover and the interior room shall have an area of
not less than 8 percent of the floor area of the interior
room or space, but not less than 20 square feet (1.86
m2). The minimum openable area to the outdoors
shall be based on the total floor area being ventilated.

Openings below grade. Where openings
below grade provide required natural ventilation, the
outside horizontal clear space measured perpendicular to
the opening shall be one and one-half times the depth of
the opening. The depth of the opening shall be measured
from the average adjoining ground level to the bottom of
the opening.

International Building Code 1203.4.1.1

Adjoining spaces. Where rooms and spaces
without openings to the outdoors are ventilated through
an adjoining room, the opening to the adjoining room
shall be unobstructed and shall have an area of not less
than 8 percent of the floor area of the interior room or
space, but not less than 25 square feet (2.3m2). The minimum
openable area to the outdoors shall be based on the
total floor area being ventilated.
Exception: Exterior openings required for ventilation
shall be permitted to open into a thermally isolated
sunroom addition or patio cover provided that
the openable area between the sunroom addition or
patio cover and the interior room shall have an area of
not less than 8 percent of the floor area of the interior
room or space, but not less than 20 square feet (1.86
m2). The minimum openable area to the outdoors
shall be based on the total floor area being ventilated.

International Building Code 1203.4.1.2

Openings below grade. Where openings
below grade provide required natural ventilation, the
outside horizontal clear space measured perpendicular to
the opening shall be one and one-half times the depth of
the opening. The depth of the opening shall be measured
from the average adjoining ground level to the bottom of
the opening.

International Building Code 1203.4.2

Contaminants exhausted. Contaminant sources
in naturally ventilated spaces shall be removed in accordance
with the International Mechanical Code and the
International Fire Code.

Bathrooms. Rooms containing bathtubs,
showers, spas and similar bathing fixtures shall be
mechanically ventilated in accordance with the International
Mechanical Code.

International Building Code 1203.4.2.1

Bathrooms. Rooms containing bathtubs,
showers, spas and similar bathing fixtures shall be
mechanically ventilated in accordance with the International
Mechanical Code.

International Building Code 1203.4.3

Openings on yards or courts. Where natural ventilation
is to be provided by openings onto yards or courts,
such yards or courts shall comply with Section 1206.

International Building Code 1203.5

Other ventilation and exhaust systems. Ventilation
and exhaust systems for occupancies and operations involving
flammable or combustible hazards or other contaminant
sources as covered in the International Mechanical Code or the
International Fire Code shall be provided as required by both
codes.