Chapter 7A requires all exterior vents on the house — whether on a wall, a foundation, or a roof — to be screened with 1/4-inch wire mesh to protect against ember intrusion. But eaves and soffits are not allowed to have vents at all, unless the vents have been demonstrated to actually resist the intrusion of both flame and ember. "And that's the hook," says Quarles. "We don't have a standard accepted method to evaluate the performance of vents to resist flame and ember."
In addition to his other duties, Quarles serves as chair of an American Society for Testing and Materials (ASTM) committee that is working on devising such a test, but the group meets only twice a year. "The test isn't there yet," says Quarles. The committee has designed and built a testing apparatus, he says, and at least three manufacturers have come up with vent designs intended to resist flame and ember, and have put their prototypes through the provisional test. "So they all have data," says Quarles, "and they are walking their data around to local building departments looking for one-off approvals."
Local officials don't have to accept any vents, however — they're free to have requirements that are tougher than the state code. In San Diego County, for instance, it's a flat rule: No vents in the soffit. Because other parts of the code still require attic venting for moisture management, builders often install flat roof-mounted vents, commonly termed O'Hagan vents after one popular manufacturer's brand name.
With soffit vents prohibited, builders adapt by installing flat-mounted rooftop vents. Models are available to blend in with synthetic slate.
Models are also available in a clay tile.
Vents must still be screened with wire mesh, as shown here viewed from below the roof sheathing.
The whole roof venting problem "leads other places," says Steve Quarles. "Do we really need to have ventilated attics? I think this is maybe going to push the unvented roof a little faster in California. There are definitely unvented attic designs out there that have been proven, especially for certain climates."
Eaves and Soffits
Besides restricting vents, Chapter 7A requires the eaves themselves to resist ignition.
An eave with wire reinforcement in place, ready for stucco application.
The completed eave presents the appearance of solid masonry.
Metal clips connect the wood structural panel sheathing to the blocking between rafters, a required seismic detail in Southern California.
There are several ways to comply, says Quarles: "You can use noncombustible material there — wrap the stucco around it, or apply a fiber-cement product such as HardieSoffit or CertainTeed WeatherBoard soffit. You can use fire-retardant-treated wood products that have met the definition for ignition-resistant material [by passing the flame tunnel test in ASTM E84], or you can pass the California state fire marshal's flame-impingement penetration test, SFM 12-7A-3." (For links to California's new wildland urban interface code and fire-marshal testing standards, visit www.jlconline.com/wildfire.)
San Diego County outlawed soffit vents years ago and provides explicit guidance for builders: Both the county building department's Web site and the Rancho Santa Fe fire prevention district's Web site supply online drawings of examples of approved soffit construction for "high" and "very high" wildfire severity zones.
San Diego County offers guidance on unvented, ignition-resistant eave details at the county planning department Web site ( www.co.san-diego.ca.us/dplu/bldgforms/index.html). One solution uses noncombustible stucco as a fireproof backer for a foam crown-molding detail.
Credit: Courtesy San Diego County Dept. of Planning and Land Use
Another uses heavy-timber rafter-tail extensions to support solid 2-by roof decking at the roof edge. In the completed assembly, stucco must cover the wall surface up to the roof deck, between the rafter tails, as well as the rest of the wall.
Credit: Courtesy San Diego County Dept. of Planning and Land Use
"Chapter 7A says that gutters shall prevent the accumulation of debris," says Quarles, "and it is silent otherwise." Gutter material isn't specified — builders can use either metal or vinyl. In practice, the rule leaves it up to local officials to approve specific gutter guards, screens, or other measures to keep litter out — with little to guide them in the task.
Quarles himself can't shed much light, noting, "If you go to their Web site, every gutter screen manufacturer, without exception, will tell you, ‘We are the best one ever.'"
In fact, there are probably differences, he says, but there is no state or national test to verify the screens' effectiveness — and anyway, all manufacturers admit that routine maintenance is still required to keep gutters clean. The "clean gutter" requirement may end up being more a homeowner responsibility than a builder issue, at least until someone comes up with a workable test for gutter screen systems.
Cliff Hunter says that in his experience vinyl gutters tend to melt and fall off when litter stuck in them catches fire — a possible advantage, since it removes the fire exposure to the roof edge.
Quarles agrees: "A vinyl gutter is going to fall to the ground pretty quickly; we've done tests, and we know this. And when that happens, how big a problem it is depends on the siding and the combustible material near the house. Metal gutters stay attached and expose your roof edge to fire, and everything then depends on your roof edge detailing. So it can be a risk either way, and it all comes back to debris in the gutter. That's why the language says just keep the debris out."
As with eaves, wall assemblies can satisfy Chapter 7A in multiple ways. Noncombustible claddings like stucco and fiber-cement are allowed; so is fire-retardant wood siding, if it can pass the ASTM E84 test (in a weathered condition, not just when brand new). Heavy timber and log construction also comply, by definition: "Just by being a log, you comply with this code," says Quarles.
But combustible materials — even wood clapboards and shingles — can also comply, at least in theory, he explains, if they can manage to pass the California fire marshal test for wall assemblies: "They're allowed to use underlying sheathing or other things to pass, and they do that by having their product tested at a commercial lab that is accredited by the fire marshal's office in the state of California."
One of California's new ignition-resistance tests is specifically designed to test windows; any that pass the test are allowed. But the alternative path is easier: Any window that is double-glazed — with at least one layer of the glazing (either inside or outside) being tempered glass — complies. "You can have any type of frame material you want," says Quarles. "It's all about the glass." (In practice, says Cal Fire chief of fire-prevention engineering Ernylee Chamlee, manufacturers have chosen to make both glazing layers with tempered glass: "They say it's just easier to do it that way.")
There are other ways to comply as well, Quarles notes. "You can use glass block. Or, you can use a window that passes the 20-minute test in ASTM standard E119, the vertical-furnace test that they use for fire-rated wall assemblies."
Of the four compliance methods, California's new test is clearly the toughest, according to Quarles; plenty of dual-glazed tempered window units have failed it. So far, in fact, no manufacturers have stepped up to make windows that can pass the California test — simply substituting tempered glazing in their existing models is far easier. That's okay, says Quarles, since the tempered glazing is a major upgrade, with proven benefits.
Even ordinary dual glazing — required by recent upgrades to California's energy codes — is much more resistant to wildfire than single glazing. In October, says Cliff Hunter, "we had 61 homes burned, and 57 of them had single-pane windows. That tells the story right there."
It's typical for fire investigators to find windows in which the outer pane has cracked or even fallen out but the inner pane is intact, keeping embers from entering the house and igniting it from the inside. And tests confirm that tempered glazing is much tougher even than regular glass: USDA Forest Service researcher Jack Cohen, for instance, has found that it takes more heat to fracture a tempered-glass windowpane than to ignite a wood wall.
When built using typical methods, wood decks are a critical vulnerability for houses exposed to wildfire. Wind tends to drop hot embers at the joint where the deck meets the house wall and ignite first the decking, then the siding. Chapter 7A requires most decking boards to pass the fire marshal's new test; redwood passes handily, and so do other woods, as well as some newly reformulated synthetic lumber products.
Combustible deck structures are a critical vulnerability in wildfire country. Here, windblown embers collected at the intersection of a wood deck and wall during October's fire, igniting the house exterior.
There are other ways to comply: Deck surfaces can be a noncombustible material such as lightweight concrete or flagstone, or they can be fire-retardant-treated wood that passes the ASTM test for ignition resistance.
Here again, Rancho Santa Fe and San Diego County have tougher restrictions: They regulate not just the deck boards on the walking surface, but also the rest of the deck structure. In San Diego County, deck supports and structures have to be of heavy timber, fire-retardant wood, noncombustible material, or one-hour fire-rated construction; otherwise, the underdeck area has to be completely skirted from deck to ground with noncombustible material.
This Ranch Santa Fe deck complies with ignition-resistant requirements because of its heavy timber framing, nominal 2x6 planking, and metal support posts and railing system.
The deck, stuccoed on the underside and topped with a proprietary noncombustible polymer waterproofing, also meets the code.
Another view of that deck shows the blackened hillside and recent green growth where the October fire swept around two sides of the house, leaving the structure undamaged.
Tougher building details alone, however, don't explain the exceptional performance of Rancho Santa Fe's "shelter in place" neighborhoods. The siting and landscaping rules in those communities made a crucial difference — and homeowners and communities who want to push beyond basic California code requirements would be wise to focus as much on the underbrush and landscaping as on hardening their buildings.
Marrying up the concepts of wildland "vegetation management" and ignition-resistant landscaping with the techniques of ignition-resistant house construction is the key to success, says Quarles: "What Chapter 7A does — and what Rancho Santa Fe's shelter-in-place concept does in spades — is make a link between the vegetation modification around your home and the materials used to build your home and the survivability of your house. There is a direct link. You cannot address just the vegetation issue or just the building materials issue. You have to do them both in order to have a home that is survivable."Ted Cushmanwrites about construction from his home in Great Barrington, Mass.