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Attached Garage Fire Containment
By Nick Gromicko, Rob London and Kenton Shepard
An attached garage is a garage that is physically attached to a house. Fires
that begin in attached garages are more likely to spread to living areas than
fires that originate in detached garages. For this reason, combined with the
multitude of flammable materials commonly found in garages, attached garages
should be adequately sealed from living areas. A properly sealed attached
garage will ideally restrict the potential spread of fire long enough to
allow the occupants time to escape the home or building.
Why are garages (both attached and detached) fire hazards?
 | Oil or gasoline can drip from cars. These fluids may collect unnoticed and
eventually ignite. |
| Flammable liquids, such as gasoline, oil and paint, are commonly stored in
garages. Some other examples are brake fluid, degreaser, motor oil, varnish,
lighter fluid, and fluids containing solvents, such as paint thinner. These
chemicals are flammable in their fluid form, and some may create explosive
vapors. |
| Heaters and boilers, which are frequently installed in garages, create
sparks that can ignite fumes or fluids. Car batteries, too, will spark under
certain conditions. |
| Mechanical or electrical building projects are often undertaken in the
garage. Fires can easily start while a careless occupant is welding near
flammable materials.
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Doors
The 2006 edition of the International Residential Code (IRC) states the
following concerning doors that separate garages from living areas:
R309.1 Opening Penetration
Openings from a private garage directly into a room used for sleeping
purposes shall not be permitted. Other openings between the garage and the
residence shall be equipped with solid wood doors not less than 1-3/8” (35 mm)
in thickness, solid- or honeycomb-core steel doors not less than 1-3/8” (35
mm) thick, or 20-minute fire-rated doors.
In addition, inspectors can check for the following while inspecting doors
that separate garages from living areas:
| While not required by the IRC, it is helpful if there is at least one step
leading up to the door from the garage. Gasoline fumes and other explosive
gases are heavier than air, and they will accumulate at ground level. Their
entry beneath a door will be slowed by an elevation increase. |
| Doors should have tight seals around their joints to prevent seepage of
fumes into the living areas of the house. Carbon monoxide, with the same
approximate density as air (and often warmer than surrounding air), 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 ajar. While this
requirement is no longer listed in the IRC, it is still a valuable
recommendation. |
| If doors have windows, the glass should be fire-rated. |
| Pet doors should not be installed in fire-rated doors. Pet doors will
violate the integrity of a fire barrier. |
Walls and Ceilings
The 2006 edition of the IRC states the following concerning garage walls and
ceilings:
R309.2 Separation Required
The garage shall be separated from the residence and its attic area by
not less than ½-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 ½-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.
In addition, inspectors can check for the following while inspecting walls
and ceilings:
| 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, as should covers made from flammable
materials, such as thin plywood. |
| The living space is 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.
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Ducts
The 2006 edition of the IRC states the following concerning ducts that penetrate
garage walls and ceilings:
R309.1.1 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 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.
Floors
The 2006 edition of the IRC states the following concerning floors in garages:
R309.3 Floor Surface
Garage floor surfaces shall be of approved, non-combustible material.
The area of the floor used for parking of automobiles or other vehicles
shall be sloped to facilitate the movement of liquids to a drain or toward
the main vehicle entry doorway.
Inspectors should also check for the following:
| A curb is present along the perimeter of the garage floor. This curb 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.
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| Water heaters should be elevated above the floor by at least 18 inches. A
pilot light may ignite spilled fluid or floor-level flammable fumes if the
water heater is placed at floor level. |
Concerning items placed on the floor, inspectors should check for the
following:
| All flammable liquids are stored in clearly labeled, self-closing
containers, and in small amounts. They should be stored away from heaters,
appliances, pilot lights and other sources of heat and flame. |
| Propane tanks should never be stored indoors. If they catch fire, a
serious explosion may result. Propane tanks are sturdy enough to be stored
outdoors. |
| The floor should be clear of clutter. Loose papers, matches, oily rags,
and other flammable items are dangerous if they are strewn about the garage
floor. |
General safety tips that inspectors can pass onto their clients:
| Use light bulbs with the proper wattage. |
| Do not overload electrical outlets. |
| Tape down all cords and wires so they are not twisted or accidentally
yanked. |
In summary, attached garages should be sealed off from the living space
so that fire may be contained.
A guidance document issued by Mecklenburg County, NC is available below. Garage Fire Walls
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