Peace of mind in wildfire country: Some common-sense advice

09/16/2020

Despite ever-longer fire seasons, people continue to live in areas like West Marin that are prone to them. While some take a fatalistic view, most will take active steps to protect their families and their homes. Architects and builders are testing new fire-hardening techniques on new construction, but these are expensive. The first priority is to save lives and the second is to keep the dwelling from burning down before firefighters can get a blaze under control. 

One of us is an architect, familiar with housebuilding in these parts. The other is a writer whose family is restoring a ridge house west of Tomales Bay. We put our heads together and came up with a seven-step program of things homeowners can do to address this ongoing challenge. If we mention brand-name products here, it’s only because they’re widely available. We have no financial ties to them. Our intent is to give you a starting point—common-sense advice that, we stress, is not a substitute for working with experienced builders and talking with the county.

Step one is defensible space. Marin County has rules and standards to follow, and its fire preparedness recommendations should be taken in advance. Clear a perimeter, trim or remove trees and bushes close to the house, and move anything that could spread fire to the interior away from windows. Most people ignore this, but holding annual fire drills so you and your neighbors know how to get out and where to meet up is important. Identify and ideally try out all possible routes. Wildfires can move fast. Keep tabs on local warning systems, because the faster you leave, the better. Remember that your life is more valuable than your house!

Step two is the roof. Avoid or replace wood or composition asphalt shingles and shakes. Fire-treated wood shingles will quickly lose their resistance. Metal or ceramic tile roofs are best. Copper or galvanized sheet metal are good; aluminum is not—it will warp in a hot fire. (Thanks to climate change, California wildfires can hit 2800° F—they are scorching.) Flat ceramic tiles or concrete tiles are good; barrel tiles are less effective because they don’t provide a good seal. 

A word about composition shingles: if you underlay them with a 72-pound cap sheet over Denglas, a gypsum product, and fire-treated plywood sheathing, you can get a class A rating. A completely incombustible roof material like ceramic tile offers better protection. In earthquake country, you need this assembly—72-pound cap sheet, Denglas and a fire-treated plywood diaphragm—to underlay whatever roof material you choose. Make sure the heavy roofing materials are well anchored to the plywood. If you opt for concrete tiles, make sure the roof framing used for the plywood diaphragm is sufficient to take the added weight. 

Got a flat roof? Cover the asphalt assembly with 12-inch square concrete tiles laid tight to keep sparks or hot ashes from setting the asphalt on fire. Use 22-gauge or thicker metal flashing on the roof perimeter so the asphalt assembly is not exposed to fire. Flash roof vents similarly.  

Step three is the walls. Avoid or replace wood boards, shingles or shakes—anything that’s combustible. The same goes for the oriented strand board, or O.S.B., which is often used today for exterior sheathing under the finish material. O.S.B. is made from wood chips, lot of glue, and formaldehyde. It is not fire resistant. Fire-treated plywood is much better.

For a wood frame, one option is a one-hour wall assembly consisting of incombustible Hardie or Borel siding with a 5/8-inch-thick gypsum underlay and fire-treated plywood sheathing. Stucco is another option, between 7/8-inch and 1-1/4 inches thick, overlaid on the same gypsum underlay and fire-treated plywood sheathing. Both options should use two-by-four or two-by-six stud wall framing, with appropriate insulation and 5/8-inch gypsum board for the interior wall finish. Two other options are steel metal stud framing and fire-treated wood stud framing. Both are more expensive. If the latter becomes mandatory in wildfire zones, greater demand is likely to reduce its cost. 

Poured-in-place, steel-reinforced concrete walls are optimal, but can be hard to install when the roads are narrow and site access to pour concrete is difficult. The cost is often prohibitive. A lower-cost option is concrete blocks or concrete masonry units. Block sizes and colors vary. Steel-reinforced and grouted, they are self-supporting. On the inside, metal channels and insulation are sheathed with 5/8-inch gypsum board. Frank Lloyd Wright used this option very creatively. Structural brick works and performs similarly, but concrete block is much more common here.

Step four is the windows. Any window frame that burns—wood, vinyl or protruded plastic—is a problem. The best options are aluminum- or steel-frame windows. For aluminum, choose commercial grade, which better resists fire. Steel is the first choice, but expensive on the West Coast. Steel can give you a one-hour fire rating; aluminum, at best, only 20 minutes. For aluminum windows, reinforce the horizontal or vertical meeting rails to prevent warping and collapse. Windows and skylights should be tempered glass. Installing metal shutters will give added protection to windows, skylights and sliding or French doors. The last are a particular hazard in fires.

Step five is the floor. A concrete slab on grade is ideal, assuming one story, but hillside sites or two or more stories rule this option out. The main issue from a fire resistance standpoint is how a wood floor assembly meets the exterior. Balloon framing is preferable, because the floors attach to the exterior wall assembly instead of penetrating it. An alternative is to make the foundation wide enough that the floor framing can sit on it separate from the exterior wall assembly. The object is to keep fire from spreading to the floor assembly, which can cause it to collapse. Next best are fire-resistant walls with crawl space ventilation that can be sealed off with metal covers. 

Step six is the decks. Use heavy timber—six-by-six or greater supports, eight-by-eight or greater for columns, and three-inch-thick decking. Fully enclose the space below the deck and don’t store things there that can burn. Decks that “hang out in space” are hazardous in fire zones. That’s the new reality. 

Step seven is to help firefighters save your house. A cistern or swimming pool, placed where gravity can drain it if you lose power, will provide backup water. The pool should be concrete; plastic melts. A standpipe on the roof will let firefighters quickly attach a hose. A fire-resistant roof ladder, already in place, will let them get up there in a hurry. Remember, these fires move with incredible speed. Minutes count. Review these measures with your fire department. Fire-resistant signs can help firefighters find what they need.

Let’s recap. Common sense includes the basics. Keep your site clear. Avoid roof and wall materials that burn readily. Put as much money as you can afford into enhancing fire resistance. Make it easy for firefighters, if it comes to that, and plan your exit per county guidelines. 

Looking ahead, it’s likely that the State of California and insurance companies will impose stricter rules about what can be built and insured in wildfire zones. Look for changes in what can be built, and for new products and assemblies. Code officials demand proof of performance, so lab testing will be part of this. Costs will rise, but as the new becomes the standard, competition enters the picture. 

 

Chuck Davis is the architect of Monterey Bay Aquarium who worked with his partner, Joseph Esherick, on the original Sea Ranch houses. He lives in Albany. John Parman, a Berkeley resident and a visiting scholar in architecture at the University of California, Berkeley, did extensive fire research as a graduate student in the 1970s. His family has a house in Inverness Park.