Fire-Resistant Construction | CRC § R302


This page introduces you to the fire-resistant construction regulations of the California Residential Code. To ensure a clear and comprehensive understanding, you need to know technical terms used within these regulations. 

The California Residential Code Sections provided are especially focused on fire safety measures for dwellings.

A "dwelling" refers to a house or a place where people live. This code applies to all types of dwellings, including single-family homes, two-family homes (like a duplex), and any accessory buildings, such as detached garages or sheds.

"Accessory structures" or "accessory buildings" are secondary buildings that exist on the same property as the main dwelling. Examples could be a tool shed or detached garage.

Here are a few key terms that you need to understand to better interpret these codes: 

  1. Fire separation distance: This term refers to the distance that must be maintained between buildings to prevent or slow the spread of fire from one building to another. It is defined in the CRC as "This distance is measured from the building face to one of the following:
    • To the closest interior lot line.
    • To the centerline of a street, an alley or public way.
    • To an imaginary line between two buildings on the lot."
  1. Automatic sprinkler system: These are systems installed in a building that automatically discharge water when a fire is detected, either by heat or smoke. These are a crucial fire safety feature in many modern buildings. It is defined in building code as, "An integrated system of underground and overhead piping designed in accordance with fire protection engineering standards. The system includes a suitable water supply. The portion of the system above the ground is a network of specially sized or hydraulically designed piping installed in a structure or area, generally overhead, and to which automatic sprinklers are connected in a systematic pattern. The system is usually activated by heat from a fire and discharges water over the fire area."
  2. Fire-resistance rating: This is a measure of how long a fire-resistive material or construction can withstand a standard fire resistance test. It is usually measured in hours or minutes. It is defined in building code as "The period of time a building element, component or assembly maintains the ability to confine a fire, continues to perform a given structural function, or both, as determined by the tests, or the methods based on tests, prescribed in Section 703."
  3. Gypsum board: This is a common construction material used for walls and ceilings, also known as drywall or plasterboard. Different thicknesses and types of gypsum board have different fire-resistance properties.
  4. ASTM E119: This is a test standard developed by ASTM International for fire tests of building construction and materials. This standard is widely used to measure and describe the response of materials, products, or assemblies to heat and flame under controlled conditions.
  5. Ducts: These are conduits or passages used in heating, ventilation, and air conditioning (HVAC) to deliver and remove air.
  6. Fireblocking: This is a building technique used to prevent the spread of fire within concealed spaces of a building such as walls and floors. It involves placing fire-resistant materials in these spaces. It is defined in building code as, "Building materials or materials approved for use as fireblocking, installed to resist the free passage of flame to other areas of the building through concealed spaces."
  7. Luminaire: This is a technical term for a light fixture, including both the lamp and its fixture.

Exterior Walls

Construction, projections, openings and penetrations of exterior walls of dwellings and accessory buildings shall comply with Table R302.1(1); or dwellings and accessory buildings equipped throughout with an automatic sprinkler system installed in accordance with section R313 shall comply with Table R302.1(2).


  1. Walls, projections, openings or penetrations in walls perpendicular to the line used to determine the fire separation distance.
  2. Walls of individual dwelling units and their accessory structures located on the same lot.
  3. Detached tool sheds and storage sheds, playhouses and similar structures exempted from permits are not required to provide wall protection based on location on the lot. Projections beyond the exterior wall shall not extend over the lot line.
  4. Detached garages accessory to a dwelling located within 2 feet (610 mm) of a lot line are permitted to have roof eave projections not exceeding 4 inches (102 mm).
  5. Foundation vents installed in compliance with this code are permitted.

Two-Family Dwellings

Dwelling units in two-family dwellings shall be separated from each other by wall and floor assemblies having not less than a 1-hour fire-resistance rating where tested in accordance with ASTM E119, UL 263 or Section 703.2.2 of the California Building Code. Such separation shall be provided regardless of whether a lot line exists between the two dwelling units or not. Fire-resistance rated floor/ceiling and wall assemblies shall extend to and be tight against the exterior wall, and wall assemblies shall extend from the foundation to the underside of the roof sheathing.


  1. A fire-resistance rating of 1/2 hour shall be permitted in buildings equipped throughout with an automatic sprinkler system installed in accordance with Section R313.
  2. Wall assemblies need not extend through attic spaces where the ceiling is protected by not less than 5/8-inch (15.9 mm) Type X gypsum board, an attic draft stop constructed as specified in section R302.12.1 is provided above and along the wall assembly separating the dwellings and the structural framing supporting the ceiling is protected by not less than ½-inch (12.7 mm) gypsum board or equivalent.

Dwelling-Garage Fire Separation

The garage and/or carport shall be separated.

  • From the residence and attics by not less than ½-inch gypsum board or equivalent applied to the garage side.
  • From habitable rooms above the garage or carport by not less than 5/8-inch Type X gypsum board or equivalent.
  • Structure(s) supporting floor/ceiling assemblies used for separation required by this section by not less than ½-inch gypsum board or equivalent.
  • Garages located less than 3 feet from a dwelling unit on the same lot by not less than ½-inch gypsum board or equivalent applied to the interior side of exterior walls that are within this area.

Dwelling-Garage Opening Protection

Openings from a private garage directly into a room used for sleeping purposes shall not be permitted. Other openings between the garage and residence shall be equipped with solid wood doors not less than 1 3/8 inches (35 mm) in thickness, solid or honeycomb-core steel doors not less than 1 3/8 inches (35 mm) thick, or 20-minute fire-rated doors. Doors shall be self-latching and equipped with a self-closing or automatic closing device.


  1. Where the residence and the private garage are protected by an automatic residential fire sprinkler system in accordance with Sections R309.6 and R313, other door openings between the private garage and the residence need only be self-closing and self-latching. This exception shall not apply to rooms used for sleeping purposes.

Dwelling-Garage Penetration Protection

Ducts in the garage and ducts penetrating the walls or ceilings separating the dwelling from the garage shall be constructed of a minimum No. 26 gage (0.48 mm) sheet steel or other approved material and shall not have openings into the garage. Penetrations through the separation required in the dwelling/garage common wall shall be protected at openings around vents, pipes, ducts, cables and wires at ceiling and floor level, with an approved material to resist the free passage of flame and products of combustion. The material filling this annular space shall not be required to meet the ASTM E136 requirements.


In combustible construction, fireblocking (two-inch nominal lumber, mineral wool, and other material per R302.11.1) shall be provided to cut off both vertical and horizontal concealed draft openings and to form an effective fire barrier between stories, and between a top story and the roof space. Fireblocking shall be provided in wood-framed construction in the following locations:

  1. In concealed spaces of stud walls and partitions, including furred spaces and parallel rows of studs or staggered studs, as follows:
    • Vertically at the ceiling and floor levels.
    • Horizontally at intervals not exceeding 10 feet (3048 mm).
  2. At interconnections between concealed vertical and horizontal spaces such as occur at soffits, drop ceilings and cove ceilings.
  3. In concealed spaces between stair stringers at the top and bottom of the run. Enclosed spaces under stairs shall comply with Section R302.7.
  4. At openings around vents, pipes, ducts, cables and wires at ceiling and floor level, with an approved material to resist the free passage of flame and products of combustion. The material filling this annular space shall not be required to meet the ASTM E136 requirements.
  5. For the fireblocking of chimneys and fireplaces, see Section R1003.19.
  6. Fireblocking of cornices of a two-family dwelling is required at the line of dwelling unit separation.

Fire Protection of Floors

Floor assemblies that are not required elsewhere in this code to be fire-resistance rated, shall be provided with a 1/2-inch (12.7 mm) gypsum wall-board membrane, 5/8-inch (16 mm) wood structural panel membrane, or equivalent on the underside of the floor framing member. Penetrations or openings for ducts, vents, electrical outlets, lighting, devices, luminaires, wires, speakers, drainage, piping and similar openings or penetrations shall be permitted.


  1. Floor assemblies located directly over a space protected by an automatic sprinkler system in accordance with Section R313, NFPA 13D, or other approved equivalent sprinkler system.
  2. Floor assemblies located directly over a crawl space not intended for storage or for the installation of fuel-fired or electric-powered heating appliances.
  3. Portions of floor assemblies shall be permitted to be unprotected where complying with the following:
    • The aggregate area of the unprotected portions does not exceed 80 square feet (7.4 m2) per story.
    • Fireblocking in accordance with Section R302.11.1 is installed along the perimeter of the unprotected portion to separate the unprotected portion from the remainder of the floor assembly.
  4. Wood floor assemblies using dimension lumber or structural composite lumber equal to or greater than 2-inch by 10-inch (50.8 mm by 254 mm) nominal dimension, or other approved floor assemblies demonstrating equivalent fire performance.

Combustible Insulation Clearance

Combustible insulation shall be separated not less than 3 inches (76 mm) from recessed luminaires, fan motors and other heat-producing devices.


  1. Where heat-producing devices are listed for lesser clearances, combustible insulation complying with the listing requirements shall be separated in accordance with the conditions stipulated in the listing.