Steven L. Smith, Bellingham, WA Home Inspector (King of the House)


An Attached Garage is Not a Fire-Rated Assembly -- Despite What You Might Have Been Told

I hear the remark, even from home inspectors, that the garage is not fire-rated or 20 minute fire-rated. Home inspectors are not code inspectors, but this kind of talk is based on codes and a misunderstanding of residential code requirements. Let's look at garage/house separation requirements. The book, Building Code Basics: Residential, was published, in part, by the IRC  (International Residential Code) which dictates most of the codes that apply to modern construction. Codes may vary from one jurisdiction to another. Below (bold) are explanations, from the IRC, that apply to garages. Below that are my comments.

"Dwelling separation from garage -- Unlike separations between dwelling units, the separation between a residence and the garage, attached or detached,  is not a fire-resistance rated assembly.  Likewise, penetrations through the separation are not required to meet the rated penetration requirements for fire-resistant assemblies. "

Interpreted: Dwellings that are connected to one another, such as condos or zero-lot-line structures or townhouses, require a fire-resistance rated assembly between the various units. However, the garage at a residence does not have the same requirements.

"Attached and detached garages, within 3 ft of the dwelling, require installation of 1/2" gypsum board on the garage side to provide "limited resistance" to the spread of a fire.  When there are habitable rooms above the garage, the code requires the installation of 5/8” type X gypsum board on the garage ceiling and the bearing wall supporting the ceiling framing requires the application of 1/2" gypsum board on the interior surface. Garage floors must be noncombustible." 


Interpreted: The proper terminology, in the case of garages, is "limited resistance to fire" and that is way short being a fire-rated assembly. Simply installing suitable drywall (often referred to as Sheetrock) in appropriate locations, will go a long way toward providing "limited resistance to fire." At any shared walls (garage to house), a noncombustible surface or drywall must extend from the floor up to the underside of the roof sheathing.  When there is a habitable room over the garage, or if the attic over the garage leads into the attic over the dwelling, a noncombustible surface or drywall must be installed on the garage ceiling and on the bearing wall that supports the ceiling framing. The flammable attic access cover, in the photo above, is a breach of fire-resistance if there is a bonus room over the garage or if the garage and house attics are connected. The garage floor, most of the time, consists of a concrete slab. If that is not the case, then the floor must be noncombustible.  

"Doors between the dwelling and the garage also provide some resistance to fire but they do not require a fire-resistance rating. Any one of the following types of doors satisfies the separation requirements:  1 3/8" thick solid-core wood door; 1 3/8" thick solid-core steel door; 1 3/8” thick honeycomb-core steel door; listed door with a 20 minute fire-resistance rating."

Interpreted: The door must be suitable for the purpose, but it need not be fire-rated -- even a wood door is acceptable if it is thick enough. Here is another requirement: There should be an operational self-closing device on all garage/house doors. The garage-house door, in the photo above, is standing wide open. That is a problem.


 "Openings from the garage into a sleeping room are prohibited."

Interpreted: That rule is self-explanatory -- doors or windows from the garage, any openings, cannot lead into bedrooms.

"The IRC requires, minimum, # 26 gauge sheet steel for ducts in the garage as well as ducts penetrating the walls or ceilings that separate the dwelling. Ducts are not permitted to open into the garage. Other penetrations, such as steel or plastic pipe, require only that the space around the penetration be filled with approved materials, such as fire-resistant caulking."

Interpreted: Ducts that pass through the garage must be made of steel and ducts cannot open into the garage. B-vents, conduit and pipes that go through walls or ceilings should be sealed, around the penetrations, with fire-resistant caulking. The duct at the garage furnace, in the photo above, is not an acceptable installation, nor is it acceptable to have that hole around the conduit at the garage/house wall.

 I am not downplaying the need to design a garage in a manner that ensures safety, but the proper terminology, to be accurate, is not "fire-rating" or "fire-rated." The proper wording is "limited resistance to fire."

Steven L. Smith

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Comment balloon 6 commentsSteven L. Smith • November 29 2011 07:15PM
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