A common problem that I see in older homes here in New Hampshire is the lack of a firewall on the shared wall with the home. See diagram below.
When I notice this flaw, many realtors will often remark that the firewall requirement is “grandfathered in,” which means it was not required when the home was built and is therefore not required now. For example, after a call to my local town building inspector, I found that it was not required prior to 1981 in my town of Bedford. On the other hand, some towns still do not have local building and code inspectors. No building inspector implies no enforcement of current codes.
However, if you are looking to bring your attached garage up to today’s safety standards, keep reading.
The Rules
The IRC 2006 edition 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.
Importantly, the firewall has to be airtight to prevent any car off gases from entering the dwelling. Thus, one is advised to check for openings in the drywall, around piping, electrical, door operators, and garage door mounting brackets and seal as needed (fire rated caulking suggested).. All drywall seams must be taped / finished with joint compound and some jurisdictions might require fire rated joint tape for this purpose.
Entry 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.
Hazards
People store propane tanks, gas grills, and flammable liquids (such as gasoline, oil and paint) in their garages. 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.
Open containers of gasoline and paint release flammable fumes that hover above the floor. For this reason any gas-fired heat source with an open flame must be at a minimum 18” above the floor to prevent ignition of gasoline fumes.
In the photo below we have a boiler in the garage with no firewall as seen with the bare insulation on the house wall side. First mistake, the paper (vapor barrier) on the insulation should of been installed on the warm house wall side.
Second issue, the electrician, if there was one, used the heating pipe runs to run electrical wires. In this case many of the wires seen were scorched from heat.
Keep in mind these heating distribution runs are open from garage to home.
Other common problems entering the garage space involve the following: heating ducts supply and return, bathroom and dryer vents.
2009 International Residential Code
M1601.6 Independent garage HVAC systems.
Furnaces and air-handling systems that supply air to living spaces shall not supply air to or return air from a garage.
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Bathroom fans improperly venting into garage space need to be rerouted to exterior. The same principle applies to dryer vents since lint is flammable; blowing it all around your garage with fuel and an ignition source is not a good idea.
The next four photos are taken from one home that a builder built, owned and was selling, unaware of the codes.
Last photo, featuring what I assumed air intake duct, was actually an air intake pulling in garage air into basement mechanical room and blowing onto 2 gas fired boilers below. The idea was to cool off the room.
“If” any open gasoline or other explosive vapors were to get sucked into the boiler room, the results could be catastrophic.
Additional safety tips
Add a smoke detector (if one is not present) for additional safety.
Change any electrical outlets over to GFCI protection, which became required in 1978.
