If a fire starts in a garage, you do not want it to spread to the attached house. Additionally, if you start up your vehicle in the garage, you do not want carbon monoxide entering your home.
Homeowners (me included) have a tendency to store an assortment of flammable materials in garages. Gas, diesel fuel, paint thinners and removers, cleaning solvents, propane cylinders, swimming pool chemicals, and other compressed gasses such as welding gas.
I have also been on many calls as a fireman where the car was started inside the garage so it can warm up. This allows carbon monoxide (CO) and other gas accumulation within the garage.
Fire separations are required between residences and attached garages and their attics. We find, and document, this issue often during our home inspections.
Here is the wording from the IRC 302.5
Openings and penetrations through the walls or ceilings separating the dwelling from the garage shall be in accordance with Sections R302.5.1 through R302.5.3.
R302.5.1 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 13/8 inches (35 mm) in thickness, solid or honeycomb-core steel doors not less than 13/8 inches (35 mm) thick, or 20-minute fire-rated doors, equipped with a self-closing or automatic closing device.
(Many communities have amended the self-closing or automatic closing device to read self-latching hardware). I haven’t memorized every community’s code (also every year of every code) about this reference. I treat the above reference by looking for a self closing device and if it is present, then it should work.
R302.5.2 Duct Penetration
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.
I just recently did a home inspection in Chicago that had the dryer vent running through the garage and exited the structure through the garage wall. This is not acceptable and I consider this a breach in the fire separation.
R302.5.3 Other Penetrations
Penetrations through the separation required in Section R302.6 (see below) shall be protected as required by Section R302.11, Item 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 E 136 requirements.) This means that fire rated sealant is not required. Typically drywall mud is installed here and that is acceptable.
R302.6 Dwelling-Garage Fire Separation
The garage shall be separated as required by Table R302.6. Openings in garage walls shall comply with Section R302.5. Attachment of gypsum board shall comply with Table R702.3.5. The wall separation provisions of Table R302.6 shall not apply to garage walls that are perpendicular to the adjacent dwelling unit wall. (This means that if there is not a living space on the opposite side of the garage wall, then the drywall is not required.)
TABLE R302.6 DWELLING-GARAGE SEPARATION
|From the residence and attics||Not less than 1/2-inch gypsum board or equivalent applied to the
|From habitable rooms above the garage||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
|Not less than 1/2-inch gypsum board or equivalent|
|Garages located less than 3 feet from a dwelling unit on the same lot||Not less than 1/2-inch gypsum board or equivalent applied to the
interior side of exterior walls that are within this area
Attic Pull-Down Stair Units
One obvious example of a ceiling fire separation breach is the near an attic pull-down stair unit. Many of the pull down stairs that I see are not designed for this installation. They do make pull down stairs that are rated for this type of installation, but those commonly are not found at the home repair stores. The photo to the left is a ladder that is designed for garage penetrations. The door of the ladder fully closes and seals when the ladder is in the up position.