CRC · California Residential Code
What are the natural light and natural ventilation requirements for habitable rooms?
Homes must provide natural light equal to **8% of a room’s floor area** and natural ventilation equal to **4% of floor area**, unless the code’s listed exceptions (artificial lighting, mechanical ventilation at 0.35 ACH, porch/sunroom conditions, etc.) apply; see **§ R325.1.1** and **§ R325.1.2** for the controlling text.
Last reviewed: July 6, 2026
What the code requires — 2-4 sentences
In plain English: habitable rooms must have enough natural light and natural ventilation sized to the room area — specifically an aggregate glazed area of at least 8% of the floor area for natural light and an aggregate openable area of at least 4% of the floor area for natural ventilation. These requirements are set out in § R325.1.1 and § R325.1.2 of the California Residential Code.
The single most important rule: provide at least 8% glazed area for natural light and 4% openable area to the outdoors for natural ventilation in each habitable room unless an allowed exception applies.
Requirements in detail
Natural light (what to size and where it must face)
- Required minimum: aggregate area of glazed openings ≥ 8% of the room’s floor area. § R325.1.1.
- Required glazed openings must face directly onto a street, alley, public way, yard or court on the same lot (there are limited exceptions). § R325.1.1.
- Alternate: artificial lighting may be used instead when it provides an average illumination of 6 foot‑candles (65 lux) at 30 in above the floor — this is a specific exception to glazed openings. § R325.1.1.
Natural ventilation (openable area and allowed openings)
- Required minimum: aggregate openable area to the outdoors ≥ 4% of the room’s floor area. Openable area may be through windows, skylights, doors, louvers or other approved openings. § R325.1.2.
- Openings must be readily accessible or readily controllable by occupants. § R325.1.2.
- Exceptions allow substitution of mechanical ventilation in certain cases (see Exceptions & special cases below). § R325.1.2.
Adjoining rooms (how rooms can count for each other)
- A room may be treated as part of an adjoining room for light/ventilation calculations when at least one‑half of the common wall area is open and unobstructed and the opening provides not less than one‑tenth (10%) of the floor area of the interior room and not less than 25 sq ft. § R325.1.3.
Decision‑relevant dimensions/values (quick reference table)
| Requirement / metric | Value / threshold | Applies to / notes | Code Reference |
|---|---|---|---|
| Natural glazed area (minimum) | 8% of the room floor area | Aggregate glazed openings (windows, glazed doors) | § R325.1.1 |
| Natural openable area (minimum) | 4% of the room floor area | Aggregate openable area (windows, skylights, doors, louvers) | § R325.1.2 |
| Artificial‑light alternative | 6 foot‑candles (65 lux) average at 30 in above floor | If provided, glazed openings are not required | § R325.1.1 (Exception 3) |
| Mechanical ventilation substitution | 0.35 air changes per hour (ACH) capability for habitable rooms | Whole‑house or zone mechanical ventilation per the Mechanical Code | § R325.1.2 (Exception 1) |
| Adjoining‑room opening for ventilation/light | ≥ 10% of interior room floor area and ≥ 25 sq ft (and half common wall open) | Counts adjoining space toward requirements | § R325.1.3 |
| Roofed porch exception (light) | porch longer side ≥ 65% unobstructed; ceiling ≥ 7 ft | Glazed openings may face into such porch | § R325.1.1 (Exception 1) |
| Sunroom / thermally isolated openings (vent) | Sunroom allowed if openable area between rooms ≥ 10% of interior room and ≥ 20 sq ft; sunroom openable to outdoors sized on combined area | § R325.1.2 (Exceptions 3 & 4) |
Exceptions & special cases
- Artificial lighting: glazed openings are not required where artificial lighting meets 6 fc (65 lx) at 30 in above the floor. § R325.1.1 (Exception 3).
- Roofed porch / patio: required glazed openings can face into a roofed porch/deck/patio that abuts a street/yard/public way when the porch’s longer side is ≥ 65% unobstructed and the ceiling height is ≥ 7 ft. § R325.1.1 (Exception 1).
- Mechanical ventilation substitute: habitable rooms (other than kitchens) do not require natural ventilation where a whole‑house mechanical ventilation system or a mechanical system capable of 0.35 ACH in the habitable rooms is installed per the California Mechanical Code. § R325.1.2 (Exception 1).
- Kitchens: natural ventilation can be omitted if a local mechanical exhaust complying with the Mechanical Code is provided. § R325.1.2 (Exception 2).
- Openings may discharge into a thermally isolated sunroom or roofed porch for ventilation when that opening meets perimeter/opening area criteria (see table). § R325.1.2 (Exceptions 3–4).
If a proposed arrangement relies on sunrooms, passive solar collectors, or openings into covered porches, read the specific exceptions carefully — they add sizing or perimeter‑open requirements and sometimes require increasing exterior glazing/openable area to “compensate.” § R325.1.1–.2.
Common mistakes
- Counting total window frame area instead of net glazed area: the requirement is the glazed opening area (glass), not the entire framed unit. § R325.1.1.
- Confusing glazed area (for light) with openable area (for ventilation). A fixed glazed unit contributes to the 8% light requirement but only openable portions count toward the 4% ventilation requirement unless other provisions apply. § R325.1.1–.2.
- Assuming any interior opening counts for adjoining room credit; the common wall must be ≥ 50% open and unobstructed and the opening must meet the 10% / 25 sq ft thresholds. § R325.1.3.
- Forgetting occupant control: required ventilation openings must be readily accessible or readily controllable by occupants — inaccessible or permanently sealed “openable” units do not comply. § R325.1.2.
Worked example — concrete numbers
Scenario: a bedroom with a floor area of 200 square feet.
Step 1 — Natural light:
- Required glazed area = 8% × 200 sf = 16 sf of glazed openings (glass area). Provide windows/doors with combined clear glazed area ≥ 16 sq ft. § R325.1.1.
Step 2 — Natural ventilation:
- Required openable area = 4% × 200 sf = 8 sf of openable area to the outdoors. This could be one window with an 8 sq ft operable sash, or two windows whose operable sash areas total 8 sq ft. § R325.1.2.
Notes and caveats:
- If the window(s) face into a roofed porch rather than directly to a yard/street, ensure the porch meets the 65% unobstructed and ≥7 ft ceiling rules, otherwise the glazing must face a yard/public way. § R325.1.1 (Exception 1).
- If a whole‑house mechanical ventilation system is installed that provides 0.35 ACH in habitable rooms per the Mechanical Code, you may omit the natural ventilation opening requirement for this room (but kitchens have separate rules). § R325.1.2 (Exception 1).
Related provisions
- § R325.1.1 — Natural light requirements (glazed area = 8% of floor area).
- § R325.1.2 — Natural ventilation requirements (openable area = 4% of floor area) and exceptions.
- § R325.1.3 — Adjoining rooms (how to count adjoining spaces toward light/ventilation).
- R325.2 — Bathroom glazing / exhaust requirements (mechanical exhaust rates and when windows are not acceptable).
- California Mechanical Code — details on mechanical ventilation rates and the 0.35 ACH mechanical substitution referenced in § R325.1.2.
Code references
Grounded in the retrieved California Residential Code — click a citation to read the verbatim passage:
CRC § 1.1 High relevance — show source text
R325.1.1 Natural light. Habitable rooms shall have an aggregate area of glazed openings not less than 8 percent of the floor area of such rooms. Required glazed openings shall face directly onto a street, alley or public way, or a yard or court located on the same lot as the building.
Exceptions:
Required glazed openings shall be permitted to face into a roofed porch, deck or patio adjacent to a street, alley, public way, yard or court, where there the longer side of the roofed area is not less than 65 percent unobstructed and the ceiling height is not less than 7 feet (2134 mm).
Required glazed openings shall be permitted to face into a sunroom adjacent to a street, alley, public way, yard or court.
Glazed openings are not required where artificial light is provided that is capable of producing an average illumination of 6 footcandles (65 lux) over the area of the room at a height of 30 inches (762 mm) above the floor level.
Eave projections shall not be considered as obstructing the clear open space of a yard or court. 5. Glazed openings may open into a passive solar energy collector provided the area of exterior glazed opening(s) into the passive solar energy collector is increased to compensate for the area required by the interior space.
R325.1.2 Natural ventilation. Habitable rooms shall have an aggregate area openable to the outdoors not less than 4 percent of the floor area of such rooms. Openings shall be through windows, skylights, doors, louvers or other approved openings to the outdoor air. Such openings shall be provided with ready access or shall otherwise be readily controllable by the building occupants.
Exceptions:
Natural ventilation shall not be required in habitable rooms other than kitchens where a whole-house mechanical ventilation system or a mechanical ventilation system capable of producing 0.35 air changes per hour in the habitable rooms is installed in accordance with the California Mechanical Code .
Natural ventilation shall not be required in kitchens where a local exhaust system is installed in accordance with the California Mechanical Code .
Required ventilation openings shall be permitted to open into a thermally isolated sunroom or roofed porch, deck, or patio where not less than 40 percent of the roofed area perimeter is open to the outdoor air.
Required ventilation openings shall be permitted to open into a thermally isolated sunroom provided there is an openable area between the adjoining room and the sunroom of not less than one-tenth of the floor area of the interior room and not less than 20 square feet (1.9 m [2] ). The minimum openable area of the sunroom to outdoor air shall be based on the total floor area of the adjoining room and the sunroom. 5. The windows, doors, louvers and other approved closeable openings not required by Section R319 may open into a passive solar energy collector for ventilation required by this section. The area of ventilation openings to the outside of the passive solar energy collector shall be increased to compensate for the openings required by the interior space.
R325.1.3 Adjoining rooms. For the purpose of determining light and ventilation requirements, rooms shall be considered to be a portion of an adjoining room where not less than one-half of the area of the common wall is open and unobstructed and provides an opening of not less than one-tenth of the floor area of the interior room and not less than 25 square feet (2.3 m [2] ).
CRC § 6.9 High relevance — show source text
R324.6.9 Testing and labeling. Unit skylights and tubular daylighting devices shall be tested by an approved independent laboratory, and bear a label identifying manufacturer, performance grade rating and approved inspection agency to indicate compliance with the requirements of AAMA/WDMA/CSA 101/I.S.2/A440.
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R324.6.9.1 Comparative analysis for glass-glazed unit skylights. Structural wind load design pressures for glass-glazed unit skylights different than the size tested in accordance with Section R324.6.9 shall be permitted to be different than the design value of the tested unit where determined in accordance with one of the following comparative analysis methods:
Structural wind load design pressures for glass-glazed unit skylights smaller than the size tested in accordance with Section R324.6.9 shall be permitted to be higher than the design value of the tested unit provided that such higher pressures are determined by accepted engineering analysis. Components of the smaller unit shall be the same as those of the tested unit. Such calculated design pressures shall be validated by an additional test of the glass-glazed unit skylight having the highest allowable design pressure.
In accordance with WDMA I.S.11.
SECTION R325—LIGHT, VENTILATION AND HEATING
R325.1 Habitable rooms. Habitable space shall be provided natural light and natural ventilation in accordance with Sections R325.1.1 through R325.1.3.
R325.1.1 Natural light. Habitable rooms shall have an aggregate area of glazed openings not less than 8 percent of the floor area of such rooms. Required glazed openings shall face directly onto a street, alley or public way, or a yard or court located on the same lot as the building.
Exceptions:
Required glazed openings shall be permitted to face into a roofed porch, deck or patio adjacent to a street, alley, public way, yard or court, where there the longer side of the roofed area is not less than 65 percent unobstructed and the ceiling height is not less than 7 feet (2134 mm).
Required glazed openings shall be permitted to face into a sunroom adjacent to a street, alley, public way, yard or court.
Glazed openings are not required where artificial light is provided that is capable of producing an average illumination of 6 footcandles (65 lux) over the area of the room at a height of 30 inches (762 mm) above the floor level.
Eave projections shall not be considered as obstructing the clear open space of a yard or court. 5. Glazed openings may open into a passive solar energy collector provided the area of exterior glazed opening(s) into the passive solar energy collector is increased to compensate for the area required by the interior space.
R325.1.2 Natural ventilation. Habitable rooms shall have an aggregate area openable to the outdoors not less than 4 percent of the floor area of such rooms. Openings shall be through windows, skylights, doors, louvers or other approved openings to the outdoor air. Such openings shall be provided with ready access or shall otherwise be readily controllable by the building occupants.
Exceptions:
CRC § 1.9 High relevance — show source text
Natural ventilation shall not be required in kitchens where a local exhaust system is installed in accordance with the California Mechanical Code .
Required ventilation openings shall be permitted to open into a thermally isolated sunroom or roofed porch, deck, or patio where not less than 40 percent of the roofed area perimeter is open to the outdoor air.
Required ventilation openings shall be permitted to open into a thermally isolated sunroom provided there is an openable area between the adjoining room and the sunroom of not less than one-tenth of the floor area of the interior room and not less than 20 square feet (1.9 m [2] ). The minimum openable area of the sunroom to outdoor air shall be based on the total floor area of the adjoining room and the sunroom. 5. The windows, doors, louvers and other approved closeable openings not required by Section R319 may open into a passive solar energy collector for ventilation required by this section. The area of ventilation openings to the outside of the passive solar energy collector shall be increased to compensate for the openings required by the interior space.
R325.1.3 Adjoining rooms. For the purpose of determining light and ventilation requirements, rooms shall be considered to be a portion of an adjoining room where not less than one-half of the area of the common wall is open and unobstructed and provides an opening of not less than one-tenth of the floor area of the interior room and not less than 25 square feet (2.3 m [2] ).
R325.2 Bathrooms. Bathrooms, water closet compartments and other similar rooms shall be provided with aggregate glazing area in windows of not less than 3 square feet (0.3 m [2] ), one-half of which shall be openable.
Exception: The glazed areas shall not be required where artificial light and a local exhaust system are provided. The minimum local exhaust rates shall be 50 cubic feet per minute (25 L/s) for intermittent ventilation or 20 cubic feet per minute (10 L/s) for contin- uous ventilation in accordance with the California Mechanical Code, Chapter 4 . Exhaust air from the space shall be exhausted directly to the outdoors.
R325.2.1 Bathroom exhaust fans. Each bathroom containing a bathtub, shower or tub/shower combination shall be mechanically ventilated for purposes of humidity control in accordance with the California Mechanical Code, Chapter 4; and the California Green Building Standards Code, Chapter 4, Division 4.5.
Note: Window operation is not a permissible method of providing bathroom exhaust for humidity control.
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R325.3 Ventilation. Ventilation air rates shall be in compliance with the California Mechanical Code.
R325.4 Opening location. Outdoor intake and exhaust openings shall be located in accordance with Sections R325.4.1 and R325.4.2.
R325.4.1 Intake openings. Mechanical and gravity outdoor air intake openings shall be located not less than 10 feet (3048 mm) from any hazardous or noxious contaminant, such as vents, chimneys, plumbing vents, streets, alleys, parking lots and loading docks.
For the purpose of this section, the exhaust from dwelling unit toilet rooms, bathrooms and kitchens shall not be considered as hazardous or noxious.
CRC § 1240.13 High relevance — show source text
1240.13 Lighting. There shall be either natural or artificial light or both for all rooms and compartments.
1240.13.1 All rooms in which poultry or livestock are killed, eviscerated or otherwise processed shall have at least 30 foot-candles (323 lux) of light intensity on all working surfaces.
Exceptions: 1. At the inspection stations such light intensity shall be at least 50 footcandles (538 lux). 2. In all other rooms in which poultry or livestock are not killed, eviscerated or otherwise processed, there shall be provided at least 5 footcandles (54 lux) of light intensity when measured at a distance of 30 inches (762 mm) from the floor.
1240.14 Ventilation. There shall be either natural or artificial ventilation, adequate to control odors, vapors and condensation to the extent necessary to prevent adulteration of product and the creation of insanitary conditions, in all rooms and compartments.
1240.14.1 Freezing rooms, other than those for plate freezers or liquid freezing, shall have forced-air circulation, and freezers and coolers shall be equipped with floor racks or pallets unless other means are used which will assure that products will be maintained in a wholesome condition.
1240.14.2 Toilet rooms shall be ventilated to the outside of the building.
1240.15 Lavatories, toilets and other sanitary facilities.
1240.15.1 Lavatory and toilet accommodations, including but not limited to, running hot and cold water, shall be provided as follows in Table 1240.15.1.
TABLE 1240.15.1 Col2 PERSONS OF SAME SEX TOILET BOWLS REQUIRED 1 to 15, inclusive 1 1 to 15, inclusive 2 1 to 15, inclusive 3* 1 to 15, inclusive 4* For each additional 30 persons in excess of 80 1* * Urinals may be substituted for toilet bowls, but only to the extent of one-third of the total number of bowls stated. * Urinals may be substituted for toilet bowls, but only to the extent of one-third of the total number of bowls stated. 1240.15.2 Lavatories shall be in or adjacent to toilet and locker rooms and at other places in the plant to provide for the cleanliness of all personnel handling products.
1240.15.3 Toilet rooms opening directly into rooms where products are exposed shall have self-closing doors.
1240.15.4 Dressing rooms and toilet rooms shall be provided in each establishment and shall be ample in size and readily accessible. They shall be separated from the rooms and compartments in which products are prepared, stored or handled. Where both sexes are employed, separate facilities shall be provided.
1240.15.5 Lockers or other facilities shall be provided for employees’ wearing apparel and for the storing and changing of clothing. Lockers shall not be located in rooms where processing operations are conducted.
CRC § 0.0283 High relevance — show source text
For SI units: 1 cubic foot per minute = 0.0283 m [3] /min, 1 cubic foot per minute = 0.4719 L/s, 1 cubic foot per minute per square foot = 5.08
[(L/s)/m [2] ], 1 square foot = 0.0929 m [2]
Where:
Vbz = breathing zone outdoor airflow, per Table 402.1. Az = zone floor area, the net occupiable floor area of the ventilation zone. W S = aggregated width of all single outdoor openings located at the same elevation.
H S = vertical dimension of the single opening or the least vertical dimension of the openings where there are multiple openings.
Volumetric airflow rates used to estimate required openable area are based on the following:
Dry-air density of 0.075 lbda/ft [3] (1.2 kgda/m [3] ) at a barometric pressure of 1 atm (101.3 kPa) and an air temperature of 70°F (21°C)
Temperature difference between indoors and outdoors of 1.8°F (1°C)
Gravity constant of 32.2 ft/s [2] (9.81m/s [2] )
Window discharge coefficient of 0.6
(2) Determine the effect of pressure losses along natural ventilation airflow paths on the resulting flow rates, including inlet openings, air transfer grills, ventilation stacks, and outlet openings during representative conditions of expected natural ventilation system use.
(3) Quantify natural ventilation airflow rates of identified airflow paths accounting for wind induced and thermally induced driving pressures during representative conditions of expected natural ventilation system use.
(4) Design to provide outdoor air in quantities sufficient to result in acceptable IAQ as established under Section 403.2.1 or ASHRAE 62.1 during representative conditions of expected natural ventilation system use. {ASHRAE 62.1:6.4.2}
402.2.3 Control and Accessibility. The means to open required operable openings shall be readily accessible to building occupants whenever the space is occupied. Controls shall be designed to coordinate operation of the natural and mechanical ventilation systems.
[ASHRAE 62.1:6.4.3]
402.3 Mechanical Ventilation. [Not permitted for OSHPD 1, 2, 3, 4 & 5] Where natural ventilation is not permitted by this section or the California Building Standards Code, mechanical ventilation systems shall be designed, constructed, and installed to provide a method of supply air and either return air or exhaust air, or both, as applicable. Mechan
|Col1|TABLE 402.2.1.6(A)(2) MINIMUM OPENABLE AREAS: TWO VERTICALLY SPACED OPENINGS* [ASHRAE 62.
CRC § 1240.6 High relevance — show source text
1240.6 Inspector’s office. Office space for the use of government personnel shall be provided. The room or space must meet the approval of the inspection service and provide for the following: 1. Light
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2. Heat
3. Ventilation
4. Desk space
5. File cabinets
1240.7 Facilities for program employees. Establishments shall have facilities for program employees.
1240.8 Lunch rooms. Lunch rooms or lunch areas separate from the processing, packing or supply rooms shall be provided in establish- ments where employees eat their lunches.
1240.9 Floors. All floors in rooms where exposed products are prepared or handled shall be constructed of, or finished with, materials impervious to moisture. The floors in killing, ice cooling, ice packing, eviscerating, cooking, boning and cannery rooms shall be graded for complete runoff with no standing water.
1240.10 Walls, posts, partitions and doors. All walls, posts, partitions and doors in rooms where exposed products are prepared or handled shall be smooth and constructed of materials impervious to moisture to a height of at least 8 feet (2438 mm) above the floor. All surfaces above this height must be smooth and finished with moisture-resistant material.
1240.11 Ceilings. Ceilings must be moisture resistant in rooms where exposed products are prepared or handled, finished and sealed.
1240.12 Rails. Rails should be located and passageway space provided so that exposed product does not come in contact with posts, walls and other fixed parts of the building or with barrels, boxes or other containers trafficked through holding and operation areas.
1240.13 Lighting. There shall be either natural or artificial light or both for all rooms and compartments.
1240.13.1 All rooms in which poultry or livestock are killed, eviscerated or otherwise processed shall have at least 30 foot-candles (323 lux) of light intensity on all working surfaces.
Exceptions: 1. At the inspection stations such light intensity shall be at least 50 footcandles (538 lux). 2. In all other rooms in which poultry or livestock are not killed, eviscerated or otherwise processed, there shall be provided at least 5 footcandles (54 lux) of light intensity when measured at a distance of 30 inches (762 mm) from the floor.
1240.14 Ventilation. There shall be either natural or artificial ventilation, adequate to control odors, vapors and condensation to the extent necessary to prevent adulteration of product and the creation of insanitary conditions, in all rooms and compartments.
1240.14.1 Freezing rooms, other than those for plate freezers or liquid freezing, shall have forced-air circulation, and freezers and coolers shall be equipped with floor racks or pallets unless other means are used which will assure that products will be maintained in a wholesome condition.
1240.14.2 Toilet rooms shall be ventilated to the outside of the building.
1240.15 Lavatories, toilets and other sanitary facilities.
CRC § 403.2.1. High relevance — show source text
Pz = Zone population: see Section 403.2.1. Ra = Area outdoor air rate, CFM/ft [2] . See Section 403.2.1.
Rp = People outdoor air rate, CFM/person. See Section 403.2.1.
Vbz = Breathing zone outdoor airflow, CFM. See Section 403.2.1.
Vdz = Zone discharge airflow, CFM. The expected discharge (supply) airflow to the zone that includes primary airflow and secondary recirculated airflow, CFM.
Vot = Outdoor air intake flow, CFM. See Section 403.3, Section 403.4, and Section 403.5.2.
Vou = Uncorrected outdoor air intake, CFM. See Section 403.5.1.
Voz = Zone outdoor airflow, CFM. See Section 403.2.3. Vps = System primary airflow, CFM. The total primary airflow supplied to all zones served by the system from the air-handling unit at which the outdoor air intake is located.
Vpz = Zone primary airflow, CFM. The zone primary airflow to the ventilation zone, including outdoor air and recirculated air.
Xs = Average outdoor air fraction: At the primary air handler, the fraction of outdoor air intake flow in the system primary airflow. Zpz = Primary outdoor air fraction: The outdoor air fraction required in the primary air supplied to the ventilation zone prior to the introduction of any secondary recirculation air. [ASHRAE 62.1:A3]
For SI Units: 1 square foot = 0.0929 m [2], 1 cubic foot per minute =
0.0283 m [3] /min, 1 cubic foot per minute = 0.4719 L/s, 1 cubic foot per
minute per square foot = 5.08 [(L/s)/m [2] ]
405.0 Ventilation for Residential Occupancies.
405.1 General. Rooms or occupied spaces within residential occupancies, where the occupants are nontransient, shall be designed to have mechanical ventilation and exhaust air in accordance with Section 405.2 through Section 405.5.
405.1.1 Natural Ventilation. Where approved by the Authority Having Jurisdiction, natural ventilation shall be permitted for Climate Zone 1, Climate Zone 2, or for thermally conditioned buildings for less than 876 hours
per year.
405.2 Ventilation Air Rate. The required mechanical ventilation outdoor air rate ( Qtot ) shall be as calculated in accordance with Equation 405.2.
Exception: For existing buildings and where permitted by the Authority Having Jurisdiction, the total mechanical ventilation ( Qtot ) is not required where Qtot is calculated to be less than 15 ft [3] /min (7.08 L/s).
Qtot = 0.03 Afloor + 7.5 ( Nbr + 1) (Equation 405.2)
Where:
Qtot = Total required ventilation outdoor air rate, CFM (L/s) Afloor = Floor area, ft [2] (m [2] ) Nbr = Number of bedrooms more than 1
For SI Units: 1 square foot = 0.0929 m [2], 1 cubic foot per minute = 0.0283 m [3] /min, 1 cubic foot per minute = 0.4719 L/s
CRC § 1.49 High relevance — show source text
Screens shall not be required where fully tempered glass is used as single glazing or the inboard pane in multiple glazing and either of the following conditions is met:
- The glass area is 16 square feet (1.49 m [2] ) or less; the highest point of glass is not more than 12 feet (3658 mm) above a walking surface; the nominal glass thickness is not more than [3] / 16 inch (4.8 mm); and for multiple glazing only the other pane or panes are fully tempered, laminated or wired glass.
- The glass is sloped 30 degrees (0.52 rad) or less from vertical; and the highest point of glass is not more than 10 feet (3048 mm) above a walking surface.
R324.6.6 Glass in greenhouses. Any glazing material is permitted to be installed without screening in the sloped areas of greenhouses, provided that the greenhouse height at the ridge does not exceed 20 feet (6096 mm) above grade.
R324.6.7 Screen characteristics. The screen and its fastenings shall: be capable of supporting twice the weight of the glazing; be firmly and substantially fastened to the framing members; be installed within 4 inches (102 mm) of the glass; and have a mesh opening of not greater than 1 inch by 1 inch (25 mm by 25 mm).
R324.6.8 Curbs for skylights. Unit skylights installed in a roof with a pitch of less than 3 units vertical in 12 units horizontal (25percent slope) shall be mounted on a curb extending not less than 4 inches (102 mm) above the plane of the roof, unless otherwise specified in the manufacturer’s installation instructions.
R324.6.9 Testing and labeling. Unit skylights and tubular daylighting devices shall be tested by an approved independent laboratory, and bear a label identifying manufacturer, performance grade rating and approved inspection agency to indicate compliance with the requirements of AAMA/WDMA/CSA 101/I.S.2/A440.
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R324.6.9.1 Comparative analysis for glass-glazed unit skylights. Structural wind load design pressures for glass-glazed unit skylights different than the size tested in accordance with Section R324.6.9 shall be permitted to be different than the design value of the tested unit where determined in accordance with one of the following comparative analysis methods:
Structural wind load design pressures for glass-glazed unit skylights smaller than the size tested in accordance with Section R324.6.9 shall be permitted to be higher than the design value of the tested unit provided that such higher pressures are determined by accepted engineering analysis. Components of the smaller unit shall be the same as those of the tested unit. Such calculated design pressures shall be validated by an additional test of the glass-glazed unit skylight having the highest allowable design pressure.
In accordance with WDMA I.S.11.
SECTION R325—LIGHT, VENTILATION AND HEATING
R325.1 Habitable rooms. Habitable space shall be provided natural light and natural ventilation in accordance with Sections R325.1.1 through R325.1.3.
CRC § 605.1.3 Medium relevance — show source text
E 605.1.3 Dwelling Unit Ventilation. A mechanical exhaust system, supply system, or combination thereof shall be designed and provided with the capacity to deliver outdoor air ventilation to the whole dwelling unit at a continuous rate not less than that specified in Section E 605.1.3.1 through Section E 605.1.3.5. [ASHRAE 62.2:4.1]
E 605.1.3.1 Total Ventilation Rate. The total required ventilation rate ( Qtot ) shall be as specified in Table E 605.1.3.1 or, alternatively, calculated using Equation E 605.1.3.1.
(Equation E 605.1.3.1) Qtot = 0.03 Afloor + 7.5( Nbr + 1)
Where:
Qtot = total required ventilation rate, CFM Afloor = dwelling unit floor area, ft [2] Nbr = number of bedrooms (not to be less than one)
For SI units: 1 cubic foot per minute = 0.00047 m [3] /s, 1 cubic foot
per minute = 0.4719 L/s
Exceptions: Dwelling-unit mechanical ventilation systems shall not be required where the Authority Having Jurisdiction determines that window operation is a locally permissible method of providing ventilation and provided one or more of the following conditions is met:
(1) The building has no mechanical cooling and is in zone 1 or 2 of the climate zone map.
(2) The building is thermally conditioned for human occupancy for less than 876 hours per year. [ASHRAE 62.2:4.1.1] E 605.1.3.2 Effective Annual Average Infiltra- tion Rate ( Qinf ) Using a Single-Point Enve- lope Leakage Test. Effective Annual Average
Infiltration Rate ( Qinf ) shall be calculated using a single-point test at 0.007 psi (50 Pa). The Effective Annual Average Infiltration Rate ( Qinf ) shall be calculated using Equation 605.1.3.2:
(Equation E 605.1.3.2) Qinf = 0.052 × Q 50 × wsf × ( H/Hr ) [z]
Where: Qinf = estimated infiltration rate, CFM (L/s). Q50 = leakage rate at 0.007 psi (50 Pa) depressurization or pressurization, CFM (L/s). wsf = weather and shielding factor from ASHRAE 62.2.
H = vertical distance between the lowest and highest above-grade points within the pressure boundary, ft (m). Hr = reference height, 8.2 ft (2.5 m). z = 0.4 for the purpose of calculating the Effective Annual Average Infiltration Rate.
For SI units: 1 foot = 0.3048 m, 1 cubic foot per minute =
0.4719 L/s
CRC § 1204.2 Medium relevance — show source text
[HCD 1] Glazed openings may open into a passive solar energy collector provided the area of exterior glazed openings in the passive solar energy collector is increased to compensate for the area required by the interior space.
1204.2 Natural light. The minimum net glazed area shall be not less than 8 percent of the floor area of the room served.
1204.2.1 Adjoining spaces. For the purpose of natural lighting, any room is permitted to be considered as a portion of an adjoining room where one-half of the area of the common wall is open and unobstructed and provides an opening of not less than onetenth of the floor area of the interior room or 25 square feet (2.32 m [2] ), whichever is greater.
Exception: Openings required for natural light shall be permitted to open into a sunroom with thermal isolation or a patio cover where the common wall provides a glazed area of not less than one-tenth of the floor area of the interior room or 20 square feet (1.86 m [2] ), whichever is greater.
1204.2.2 Exterior openings. Exterior openings required by Section 1204.2 for natural light shall open directly onto a public way, yard or court, as set forth in Section 1205.
Exceptions:
- Required exterior openings are permitted to open into a roofed porch where the porch meets all of the following criteria:
1.1. Abuts a public way, yard or court. 1.2. Has a ceiling height of not less than 7 feet (2134 mm). 1.3. Has a longer side at least 65 percent open and unobstructed. 2. Skylights are not required to open directly onto a public way, yard or court.
1204.3 Artificial light. Artificial light shall be provided that is adequate to provide an average illumination of 10 footcandles (107 lux) over the area of the room at a height of 30 inches (762 mm) above the floor level.
1204.4 Stairway illumination. Stairways within dwelling units and exterior stairways serving a dwelling unit shall have an illumination level on tread runs of not less than 1 footcandle (11 lux). Stairways in other occupancies shall be governed by Chapter 10.
1204.4.1 Controls. The control for activation of the required stairway lighting shall be in accordance with the California Electrical Code.
1204.5 Emergency egress lighting. The means of egress shall be illuminated in accordance with Section 1008.1.
1204.6 Light pollution reduction. [BSC-CG] See California Green Building Standards Code, Chapter 5, Division 5.1 for additional light pollution reduction requirements.
1204.7 Campus lighting for parking facilities and primary walkways at California state universities, colleges and community colleges. [BSC] Artificial light shall be provided for parking facilities and primary walkways at California State Universities, colleges and community colleges in accordance with provisions of this subsection. This subsection shall not apply to the University of California unless the Regents of the University of California, by resolution, make it applicable.
CRC § 12-6 Medium relevance — show source text
1.2. Group F, H, S or U occupancies. 2. [HCD 1] For limited-density owner-built rural dwellings, a heating facility or appliance shall be installed in each dwelling subject to the provisions of Subchapter 1, Chapter 1, Title 25, California Code of Regulations, commencing with Section 74; however, there shall be no specified requirement for heating capacity or temperature maintenance. The use of solid-fuel or solar-heating devices shall be deemed as complying with the requirements of this section. If nonrenewable fuel is used in these dwellings, rooms so heated shall meet current installation standards. 3. [OSHPD 1, 1R, 2, 3, 4 & 5] Space heating systems shall comply with the requirements of the California Mechanical Code. 4. [HCD 1] When a passive solar energy collector is designed as a conditioned area it shall comply with the California Energy Code. Nonconditioned passive solar energy collectors are exempt from compliance with the California Energy Code.
12-6 2025 CALIFORNIA BUILDING CODE
on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.
INTERIOR ENVIRONMENT
SECTION 1204—LIGHTING
1204.1 General. Every space intended for human occupancy shall be provided with natural light by means of exterior glazed openings in accordance with Section 1204.2 or shall be provided with artificial light in accordance with Section 1204.3. Exterior glazed openings shall open directly onto a public way or onto a yard or court in accordance with Section 1205.
[HCD 1] Glazed openings may open into a passive solar energy collector provided the area of exterior glazed openings in the passive solar energy collector is increased to compensate for the area required by the interior space.
1204.2 Natural light. The minimum net glazed area shall be not less than 8 percent of the floor area of the room served.
1204.2.1 Adjoining spaces. For the purpose of natural lighting, any room is permitted to be considered as a portion of an adjoining room where one-half of the area of the common wall is open and unobstructed and provides an opening of not less than onetenth of the floor area of the interior room or 25 square feet (2.32 m [2] ), whichever is greater.
Exception: Openings required for natural light shall be permitted to open into a sunroom with thermal isolation or a patio cover where the common wall provides a glazed area of not less than one-tenth of the floor area of the interior room or 20 square feet (1.86 m [2] ), whichever is greater.
1204.2.2 Exterior openings. Exterior openings required by Section 1204.2 for natural light shall open directly onto a public way, yard or court, as set forth in Section 1205.
Exceptions:
- Required exterior openings are permitted to open into a roofed porch where the porch meets all of the following criteria:
1.1. Abuts a public way, yard or court. 1.2. Has a ceiling height of not less than 7 feet (2134 mm). 1.3. Has a longer side at least 65 percent open and unobstructed. 2. Skylights are not required to open directly onto a public way, yard or court.
CRC § 402.2 Medium relevance — show source text
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402.2 Natural Ventilation Procedure. [Not permitted for OSHPD 1, 2, 3, 4 & 5] Natural ventilation systems shall comply with the requirements of either Section 402.2.1 through Section 402.2.1.6(A) or Section 402.2.2. Designers shall provide interior air barriers, insulation, or other means that separate naturally ventilated spaces from mechanically cooled spaces to prevent high-dew-point outdoor air from coming into contact with mechanically cooled surfaces.
[ASHRAE 62.1:6.4]
402.2.1 Prescriptive Compliance Path. Any zone designed for natural ventilation shall include a mechanical ventilation system designed in accordance with Section 403.0.
Exceptions:
(1) Zones in buildings that have all of the following:
(a) Natural ventilation openings that comply with the requirements of Section 402.2.1.
(b) Controls that prevent the natural ventilation openings from being closed during periods of expected occupancy, or natural ventilation openings that are permanently open.
(2) Zones that are not served by heating or cooling equipment. {ASHRAE 62.1:6.4.1}
402.2.1.1 Ceiling Height. For ceilings that are parallel to the floor, the ceiling height ( H ) to be used in Section 402.2.1.3 through Section 402.2.1.5 shall be the minimum ceiling height in the zone.
For zones where ceiling height increases as distance from the openings is increased, the ceiling height shall be determined as the average height of the ceiling within 20 feet (6096 mm) from the operable openings. [ASHRAE 62.1:6.4.1.1]
402.2.1.2 Floor Area to be Ventilated. The nat urally ventilated area in zones or portions of zones shall extend from the openings to a distance determined in accordance with Section 402.2.1.3, Section 402.2.1.4, or Section 402.2.1.5. Openings shall be in accordance with the requirements of Section 402.2.1.6.
For zones where ceilings are not parallel to the floor, the ceiling height shall be determined in accordance with Section 402.2.1.1. [ASHRAE 62.1:6.4.1.2]
402.2.1.3 Single Side Opening. For zones with openings on only one side of the zone, the naturally ventilated area shall extend to a distance not greater than 2 times the height of the ceiling from the openings. [ASHRAE 62.1:6.4.1.3]
402.2.1.4 Double Side Opening. For zones with openings on two opposite sides of the zone, the naturally ventilated area shall extend between the openings separated by a distance not greater than 5 times the height of the ceiling. [ASHRAE 62.1:6.4.1.4]
70 2025 CALIFORNIA MECHANICAL CODE
), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.
VENTILATION AIR
TABLE 402.2.1.6(A)(1) MINIMUM OPENABLE AREAS: SINGLE OPENINGS*
Frequently asked questions
What counts as “glazed openings” for the 8% natural light rule?
“Glazed openings” means the net area of glazing (glass) in windows, glazed doors, skylights, etc., that face the required exterior space. The code requires aggregate glazed area ≥ 8% of the room floor area. § R325.1.1.
Do skylights count for natural ventilation?
Yes — the code lists skylights among acceptable openings for natural ventilation (openable skylights) and they can contribute to the 4% openable area if they are openable to the outdoors. § R325.1.2.
Can I use mechanical ventilation instead of windows?
Yes. Habitable rooms (other than kitchens) do not require natural ventilation if a whole‑house or zonal mechanical ventilation system capable of 0.35 ACH in the habitable rooms is installed per the California Mechanical Code. § R325.1.2 (Exception 1).
If two rooms share a large open opening, how do I size glazing/ventilation?
Rooms can be considered portions of an adjoining room when ≥ 50% of the common wall is open and unobstructed and the opening is ≥ 10% of the interior room floor area and ≥ 25 sq ft. Use § R325.1.3 to determine whether adjoining room area may count.
What if I provide the required light/vent through a sunroom or passive solar collector?
Exceptions allow openings to face into sunrooms or passive solar collectors only when the code’s compensation and perimeter/opening conditions are met (sometimes requiring increased exterior glazing/openable area). Check § R325.1.1–.2 for the specific exception language.
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