Napa architect Chris D. Craiker, AIA, NCARB, has been committed to designing affordable and sustainable housing for nearly 50 years. Contact him at 707-224-5060 or chris@craiker.com. Read his previous column.
This year marks the 30th anniversary of the Auckland fire, which destroyed more than 3,400 housing units and killed 25 people.
For the past 30 years, my company has been rebuilding and reimagining dozens of houses destroyed by the frequent fires that have swept Northern California.
In 2007, the state authorized the Wildlife Urban Interface—WUI, pronounced woo-EE—to provide additional protection for buildings throughout California's rural and restricted areas.
We call it "fire prevention". The basic requirement is that all new structures in rural areas or areas where fire-fighting equipment is not so accessible are flame-resistant to resist flying embers and rapid wildfire radiation. It quickly became part of the international building code.
A brief summary of WUI requirements is to use refractory materials to reinforce the exterior, minimize the burning vegetation around the house, and minimize the vents under the house or in the attic.
Even stucco houses will explode from the inside when the fire is approaching, entering through the vents under the floor.
Our standard method is to use flame-retardant materials such as cement fiber board (CFB), paneling or plaster. We also use metal corrugations to create an avant-garde modern look.
Recently, one of our clients, we reimagined and rebuilt his destroyed house. His insurance company ran into trouble, and the company insisted that they should re-pave their new house with wood because it was the same. The insurance company cited a section that allowed a thin layer of slate to be placed on the outside and covered with "wood" to match the previous sheath.
The specification specifies fire-resistant treated wood (FRTW) as an acceptable exterior material.
But this is notoriously unstable and the weather is bad. In the 1980s, shingle or shaky roofs were banned, and roofers were required to replace aging roofs with composite shingles, concrete tiles or fire-retardant tiles.
If you are lucky, the latter may last for 10 years. Painting or dyeing will eliminate the flame retardant value and make it useless. Except for the exotic hardwood Ipe from South America, no wood meets the fire protection requirements of the specification. It is one of the hardest, toughest, and most expensive woods.
Only materials that are truly refractory should be considered, such as cement fiberboard or stucco or metal. In my professional opinion, FRTW should not be used at all.
One of the main considerations for WUI fire hardening is to protect the structure from fire damage.
The basic premise of building codes is to slow the spread of fire and allow occupants to escape the building. This is the fundamental difference between the two coding methods.
The building code admits that the one-hour construction includes gypsum board under external flammable materials (such as red planks or shingles) as a finishing material, thereby allowing residents to leave. It is not designed to preserve structure.
In discussions with building code enforcement professionals, it was generally agreed that the use of FRTW has long-term disadvantages.
I spoke with Mike Zimmer, the chief construction officer of Napa County, and he agreed that this use should not be considered a long-term refractory.
He pointed out that these products are impregnated with toxic ammonium phosphate, sulfate, borax and zinc chloride, which lose their effectiveness and accelerate wood degradation much faster than the manufacturer admits.
Owners and occupants of more than 6,000 structures that have not been rebuilt during the Northern California fire in the past four years should check with their insurance company to confirm their correct interpretation of California’s WUI requirements.
Companies from out of state usually don't know anything about the construction cost differences we encounter here. I studied the cost of plaster and wood, and found that the cost of plaster is 5 to 9.58 US dollars per square foot, which is suitable for ordinary new houses, and the installation cost of natural wood siding is on average 6 to 12 US dollars per square foot. This does not take into account the higher cost of the imperfect product FRTW.
You must wonder whether these insurance companies are protecting their customers or preparing for future liability avoidance. I have been practicing architecture long enough to understand how insurance companies manipulate the market.
He said that when they are safe and reliable, he likes shingle-designed houses.
Napa architect Chris D. Craiker, AIA, NCARB, has been committed to designing affordable and sustainable housing for nearly 50 years. Contact him at 707-224-5060 or chris@craiker.com. Read his previous column.