What are the code requirements for fire separation between an attached garage and the house?
Tuesday, December 4, 2018
There are requirements for the walls and ceiling, door to the house, HVAC ducts, and any other garage/house penetrations. Let’s take them one at a time:
WALLS AND CEILING - The wall between an attached garage and the house living area is required to be minimum 1/2” drywall. Most garages have a ceiling secured to the bottom chord of the roof trusses or rafters, and that has to be 1/2” drywall also. If there is no ceiling and the roof structure is exposed in the garage, then the wall separating the garage from the dwelling must extend up to the underside of the roof sheathing. There is a high incidence of fires started in garages due to the gasoline and other flammable materials often stored there and, either way, the intent is create a 1/2” drywall barrier between the garage and house for fire protection.
Only common walls between garage and house (not perpendicular walls) must meet this requirement. If a garage is detached, but within 3-feet of the residence, any walls within 3-feet must have 1/2” drywall. When there is a living area (habitable space) above the garage, the ceiling requirement ramps up to 5/8” Type X fire-rated drywall.
While all of this is intended to create a fire barrier between garage and house, it is not specified as “one-hour rating” or “fire wall” by the Residential Editon of the Florida Building Code (FBC) or the International Residential Code (IRC). It is called a “separation."
Here’s Table 302.6 from the Residential Editon of the Florida Building Code that spells out these requirements. The International Residential Code table is similar.
DOOR TO HOUSE - This is the only place where any fire rating is specified. If the door is not solid wood or steel/honeycomb and at least 1-3/8” thick, then it must have a 20-minute fire rating. By the way, cutting a hole in the door to install a pet-door flap voids the 20-minute rating. Installing a steel door with a glass panel in it also voids the rating unless the glass is fire-rated too, which is obtainable but very expensive. See our blog post What are the building code requirements for a door from the garage to the house? for more on this.
HVAC DUCTS - Any heating/air conditioning ducts that serve the residence cannot also have registers (vents) in garage. Any register would provide a direct route for a fire to move from the garage to house. A separate HVAC system that serves only the garage is acceptable.
Furnaces and air handlers are often installed in the garage, and the code requires the ducts to be either minimum no. 26 gauge sheet steel, or rigid nonmetallic Class 0 or Class 1 board, or other material approved by the AHJ (building department).
"Class 0" is defined as air ducts and connectors having burning characteristics of zero. "Class 1" means air ducts and connectors having a flame-spread index of not over 25 without evidence of continued progressive combustion and a smoke-developed index of not over 50. The duct boards are marked with their class rating as an imprint or sticker on the board.
Any type of register or grille in the ceiling of the garage that opens directly into the attic over the home is not allowed. We occasionally see vents retrofitted to provide ventilation to cool a hot garage in the summer, or to provide combustion air for a gas furnace or water heater in the garage. Shown below is an example of what not to do (a grille cut into pull-down attic ladder), and an example of the right way to add a vent a register in the ceiling of garage that connects directly to a roof vent via a metal duct, viewed from the attic.
Combustion air (also called “make-up air”) can also be provided by a vent through the wall. The two photos below show an outside and inside view of an example of this.
OTHER PENETRATIONS - Required by 3.2.11, Item 4, of FBC that any openings around vents, pipes, ducts, cables, and wires at ceiling and floor be sealed with an approved material (approved by AHJ) to resist the free passage of flames and products of combustion. The material filling the annular (ring-shaped) space around the penetration does not have to meet the ASTM E136 standards.
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