When houses are surveyed for wildfire vulnerabilities, quite often the garage is not considered even though it could be the most hazardous aspect of the house.
Attached Garages: Potential Problems
Garages are typically not well sealed since they are generally not heated or cooled. Gaps at the top, bottom and edges of doors can let glowing embers enter, and we all know that garages are full of flammable materials. Garages usually have vents at various locations, especially if they contain gas furnaces or hot water heaters. These vents are easy entry points for embers.
These photos show a full-size roll-up garage door that has not been properly adjusted, creating a gap at the right bottom where embers could easily enter.
Small embers can easily enter through the door gaps. Sliding doors (that are hung at the top edge) have a special problem in that one side is offset, leaving a large gap at the top edge. In addition, many garage doors have glass in the top sections plus personnel entry doors that have single pane glass that (although it is tempered in newer construction) can easily be broken from heat or flying debris. For more information on glass, see the section on Windows.
This garage car door has glass panels that could break during wildfire exposure, including vertical flamespread up the combustible door. Some current door manufacturers advertise that their glass panels are tempered.
The window in this particular door is tempered glass, but is also single pane which does not offer a great amount of wildfire protection.
An even greater concern is attached carports or any type of garage that does not have doors. These types of garages would typically have an extreme number of combustibles and many nooks and crannies for embers to lodge.
Attached Garages: Possible Solutions
For garages with roll-up doors, the top and bottom can be weatherstripped (quite often the bottom is sealed to prevent water entry). The roll-up mechanism should be adjusted to obtain a good seal at the top. Tilt-type doors have similar solutions, although sealing at all edges is easier.
The vertical edges on roll-up doors are also a problem in that weatherstripping is not usually an option, however, non-contacting materials can be added that baffle the direct movement of air through the edges, as shown in the first picture. In this photo, a small piece of 2x4 has been tacked on to show how the upper opening in the framing could be blocked if it were extended the full width. The next photo shows the door closed and how the upper opening is blocked. Of course, most of these doors are not installed with that upper trim.
For attached carports, as a first step, combustibles should be minimized. However, this would still present the greatest hazard to your home, and some serious thought should be given to have the garage properly enclosed.
Car-entry garage doors with glass panels can either have the panels replaced with fire-rated glass or simply filled in.
Personal entry doors with windows can also have the windows replaced with fire-rated material or the window could be replaced with paneling. Another solution is to consider a stell-clad door as shown below, which provides both fire resistance and security from break-ins.