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.


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, InterNACHI 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, the following should also be checked:

  • 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. 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 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.
  • 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.


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.


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.

The following should also be checked:

  • 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.
  • 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, 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:

  • 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.