Monday, December 10, 2012

Understanding Firewalls in Buildings


Firewalls are one of the most important, yet least understood safety items that a home inspector checks. It is one of the many passive safety features built into a house that is often over-looked during a home inspection. Just like the air bag in your car we hope that it is never needed.
The intent of the firewall between the attached garage and the living space is intended to slow the spread of fire from the garage to the living space. In order to accomplish this several components of a house must be made of fire resistive materials, and all must be working together for the system to work. Drywall used on the garage side of walls shared with living space must have a one hour fire resistive surface. If the garage ceiling is not covered with drywall,
Fire wall to roof
Fire wall to roof
 then the common walls between the garage and living space must be covered all the way up to the underside of the roof sheating. You may see open rafters in the garage which is OK as long as there is no living space above the garage. In this example, if a fire starts in the garage, it cannot easily spread to the living space, or the attic above the living space. It will be contained to the garage.
In the picture below, there are numerous breaches in the firewall which must be addressed to restore the integrity of the firewall. Even though the fire-rated drywall extends up to the roof, a section of drywall was removed by the water heater due to some water damage. This must be patched. Fire could otherwise race up the wall if the water heater caught on fire. Other breaches include a missing switchplate cover at the garage light switch, and large holes in the drywall above the furance where the refrigerant lines pass into the attic. Finally, the fire rated door does not have a functional auto-closing device which is required in Florida to keep this door closed.
Several breaches observed in this firewall
Several breaches observed in this firewall

When the garage is “finished” and no framing members are exposed, the ceiling of the garage should be covered with 5/8 inch thick fire-rated drywall. In one story houses, this is necessary when the attic space over the house and garage are open, and there is no firewall between the space over the garage, and over the house.
Unfortunately many homeowners install pull-down ladders to access the attic space above the garage for storage.
Firewall required at ceiling of garage
Firewall required at ceiling of garage
 The problem is that most pull down ladders are not fire-rated. They are typically covered with a thin sheet of plywood that would quickly burn in the event of a fire. Homeowners who understand the concept of a firewall often try to remedy this by attaching a piece of drywall to the underside of the pull down ladder. The intent is that when it is in the closed position it should restore the integrity of the firewall ceiling. Most of the time the added weight of the drywall prevents the ladder from closing all the way leaving a gap. This gap will allow fire to get into the attic and is a breach 
of the firewall.
Note: wood pull-down ladders are acceptacle when a firewall exists in the attic between the areas above the garage and house. Fire-rated pull-down ladders are available.
Another common homeowner mistake is to installed recessed lights in the garage. When doing so, a box must be constructed around the light fixture to maintain the fire-retardancy of the ceiling. This can be done by using fire-rated drywall.
We often see holes cut into the firewall in attics between the garage and living space. These are often done to run
Hole in attic firewall
Hole in attic firewall
wires, or access a portion of the attic more easily. Your home inspector should be catching these items for repair as they are safety hazards. All breaches in the firewall must be patched. All drywall seams must be properly sealed with drywall compound, and small holes and penetrations must be filled with a firewall caulking.
Finally, the door between the garage and living space must be a fire-rated door. In most municipalities in Florida this door must be fire-rated to resist burn through for 20 minutes. This door can be a solid wood door or a metal door. The doors should have a fire rating tag on the top edge of the door, or at the hinge edge of the door. but these are often removed or painted over. In addition to being fire-rated, this door must close and latch without assistance. This is accomplished with a spring loaded hinge or a gas shock mounted at the top of the door.  
While this post is neither an exhaustive explanation of the building fire code, nor a substitute for a professional evaluation, it should give you a good idea of what home inspectors look for in the garage. If you have specific questions about the requirements for your house, please check with your local building department or a local home inspector.

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