Many home especially more modern homes are constructed with attached and built in type garages. Fires that start in an attached garage can easily spread to the home. Attached garages must be adequately sealed off from the living space. The idea is not so stop a fire from spreading but to provide the occupants a little more time to escape the home during a fire emergency.
Attached garages are fire hazards because of:
Oil, gasoline or other flammable liquids are often stored inside the attached garage. Some of these flammable liquids can create vapors that can cause an explosion when ignited. Heaters and boilers which are often installed in garages can ignite flammable vapors. Mechanical or electrical building projects are often undertaken in the garage. Fires can easily start while an occupant is doing shop work in the garage. There must be a fire rated door that separates the garage from the home.
Although not required by the International Residential Code (IRC), it is beneficial to have at least one step leading up to the door from the garage. Gasoline vapors and other explosive gases are heavier than air, and will accumulate close to the floor. The entry of flammable gas under the door will be slowed by an a raised threshold or other increase in height. Doors should have tight seals around their joints to prevent fumes from entering into the living space. Carbon monoxide has almost the same density as air and will easily rise above the base of an elevated door and leak through unsealed joints. Doors should be self-closing. Many homeowners find these doors inconvenient, but they are safer than doors that can be left in the open position. While this requirement is no longer listed in the IRC, it is still a valuable recommendation. The doors should not have non fire rated windows of any kind. Cut out dog or cat doors should not be installed in fire-rated doors. These doors will breach the integrity of a fire barrier.
The following is an excerpt from the IRC pertaining to attached garages.
The garage shall be separated from the residence and its attic area by not less than 1/2-inch (12.7 mm) gypsum board applied to the garage side. Garages beneath habitable rooms shall be separated from all habitable rooms above by not less than 5/8-inch (15.9 mm) Type X gypsum board or equivalent. Where the separation is a floor-ceiling assembly, the structure supporting the separation shall also be protected by not less than 1/2-inch (12.7 mm) gypsum board or equivalent. Garages located less than 3 feet (914 mm) from a dwelling unit on the same lot shall be protected with not less than 1/2–inch (12.7 mm) gypsum board applied to the interior side of exterior walls that are within this area. Openings in these walls shall be regulated by Section 309.1. This provision does not apply to garage walls that are perpendicular to the adjacent dwelling unit wall.
New Jersey Home Inspectors can check for the following while inspecting walls and ceilings:
The attic access hatch should also be fire rated. In garages that have access to the attic, a hatch cover made from an approved, fire-rated material should protect this access at all times. Missing or opened covers should be called out by home inspectors, as should covers made from flammable materials, such as thin plywood. Garage attic door must be constructed such that the 45 minute rating is maintained; any drywall edges on both the hatch and the surrounding area exposed to physical damage are protected. The cover or door is installed so that it is permanent (non removable) with hardware to maintain it in a closed position with latching hardware to maintain it in a closed position. This could be accomplished by the use of spring loaded hinges, door closer, or hardware that will not allow it to be left in an open position when not in use. A single bolt type or hook and eye hardware does not provide a positive closure since these would allow the door to be left open. Likewise drywall screws are “fasteners” and not hardware so they cannot be used as the only means of keeping access doors closed.
The living space has to be separated from the garage by a firewall that extends from the floor to the roof. If the ceiling material is fire-rated, the firewall can terminate at the ceiling.
Drywall joints shall be taped or sealed. Joints shall be fitted so that the gap is no more than 1/20-inch with joints backed by either solid wood or another layer of drywall such that the joints are staggered.
Any duct work in the attached garage is required to be rigid.
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 gauge (0.48 mm) steel sheet or other approved material, and shall have no openings in the garage.
Dryer exhaust ducts that penetrate garage walls are serious fire hazards. These ducts are generally made from plastic and will easily melt during a fire, creating a large breach in the firewall.
Inspectors should also check for the following:
NJ Home inspectors should make sure a curb is present along the perimeter of the garage floor. This type of curbing is designed to prevent fluids from entering the living areas of the house. Curbs are often useful barriers for melted snow carried into the garage by automobiles, but curbs can also keep chemical spills contained in the garage.
Water heaters should be raised above the floor by at least 18 inches. A pilot light can ignite flammable fumes and vapors if the water heater is placed at floor level.
All flammable liquids should be stored in labeled, self-closing approved containers, and in small volumes. Flammable liquids should be stored away from heaters, appliances, pilot lights and other sources of heat and flame.
Propane tanks should never be stored in garages. If they catch fire, an explosion may result. Propane tanks are sturdy enough to be stored outside.
In summary, attached and built in garages should be sealed off from the living are so that fire may be contained and occupants have a greater chance of escaping the home in the event of a fire emergency.