Geoscience Reference
In-Depth Information
• Use only “Class A” fire-rated roofing systems, which are rated to prevent both the
roofing material itself, and roofing underlayment (plywood) from catching fire when
covered with burning embers. Most asphalt and fiberglass shingles are Class A rated,
but metal roofing usually requires the use of Versashield underlayment (or equal) to
achieve this rating. “Living” roofs (planted sod) have excellent fire resistance as well
as thermal mass and insulation. With Class A roofing, the eaves and overhangs are
the most vulnerable areas of the roof owing to the fire down below.
(Adapted and expanded from John Underwood, “Fire Resistant Details: Studying the Houses That Survived the
1993 Laguna Beach Fire Storm Yields Lessons in Building to Withstand the Heat,” Fine Home Building.com)
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My buddy Jim Bolton, an experienced Reno fireman, tells me that when they enter a neighborhood, they take mental
notes about which homes have maintained a defensible space and which have not. They don't waste their time focus-
ing on homes without a defensible space, but spend their time defending homes where they stand a decent chance of
success, while keeping a watchful eye on nearby flames. These are brave guys, risking their necks where most of us
would not go, but they have wives and kids, so when a vicious fire storm gets dangerously close, they simply have to
leave the neighborhood and let nature take its course.
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There are a number of building systems that are inherently fire resistant. Basically, if it is
earth or concrete based, it is very fire resistant. Also, if you fill the wall with foam or straw, to
eliminate dead air spaces and the chimney effect, and sheath the wall with stucco, earthen
plasters, or cement board, even if it is wood-framed it will have good fire resistance. Do your
best to make your roof, eaves, and decks fire resistant too, since your home will only be as fire
resistant as its weakest link. Obviously, traditional stone, brick, and concrete-block construc-
tion are also quite fire resistant, provided their roofs are not a weak link in the system.
With burning embers settling on rooftops, in many cases it is the roof that forms the weak
link in the fire-resistance chain. Traditional wooden shake and shingle are notorious for catch-
ing on fire from burning embers. For fire-resistant roofing, consider the following options:
• Use only “Class A” fire-rated roofing.
• Class A roofing must withstand burning embers on roof without igniting plywood
sheeting.
• Most modern composition (asphalt) shingles are “Class A” fire-rated.
• Metal roofs transmit heat easily to the underlying plywood, so they tend to be not as
fire resistant as you might imagine, unless they are underlaid with an insulating
flame-resistant lining. They are usually only Class A fire resistant with the addition
of Versashield underlayment (or similar).
