USA – This year is the 30th anniversary of the Oakland fire that destroyed over 3,400 housing units and 25 people died.
In the last 30 years, my firm has been reconstructing and reimagining scores of destroyed homes from the frequent fires that have ravished Northern California.
In 2007, the state mandated the wildlife urban interface — WUI, pronounced woo-EE — extra protection to construction in rural and limited accessible areas throughout California.
We call it “fire hardening.” The basic requirement is that all new structure exteriors in rural or less fire apparatus accessible areas be ignition-resistant to resist the entry of flying embers and rapid wildfire radiation. It soon became a part of the International Building Code.
In dramatic demonstrations in Sonoma County this week, fire officials show how common homebuilding materials take the heat during a blaze and what can be done to help prevent future disasters like the 2017 fires.
A brief summary of WUI requirements is hardening exteriors with fire resistant materials, minimizing fire ignition vegetation around the house and minimizing vents under the house or into the attic.
Even stucco homes have been known to explode from the inside when fires approach, entering through under floor vents.
Our standard approach is to use fire retardant materials such as cement fiber board (CFB), paneling or stucco. We also use metal corrugated for that edgy contemporary look.
Recently one of our clients, whose destroyed home we had re-imagined and reconstructed, was having trouble with his insurance company which insisted they should have resurfaced their new home in wood, because that was what was there originally. The insurance company was citing a section that allows a layer of sheet rock to be placed on the exterior and cover with “wood” to match the previous sheathing.
The code specifies fire-resistant treated wood (FRTW) as an acceptable exterior material.
But this is notoriously unstable and weathers poorly. In the 80s, wood shingle or shake roofs were outlawed and roofers were required to replace deteriorating roofs with composition shingle, concrete tile or fire-retardant shingles.
The latter lasted maybe 10 years, if one was lucky. Painting or staining eliminates the fire-retardant value and renders it useless. There is no wood that meets the fire-resistant requirements of the code except Ipe, an exotic hardwood from South America, that is among the hardest, toughest, most expensive woods available.
Only truly fire-resistant materials such as cement fiber board or stucco or metal should be considered. In my professional opinion, FRTW should not be used at all.
One major consideration of fire hardening, WUI is to save the structure from fire destruction.
The basic premise of the building code is to slow a fire spreading and allow the occupants to escape the structure. This is a fundamental difference in the approach of the two codes.
The building code recognizes one hour construction to include sheetrock under an exterior flammable material such as redwood planking or shingle as a finish material, thus allowing the inhabitants to exit. It is not designed to save the structure.
In discussions with building code enforcement professionals, there is general agreement that the use of FRTW has long-term disadvantages.
I talked with Mike Zimmer, Napa County chief building official, who agreed that the use should not be considered as a long-term fire-resistant material.
He pointed out that these products are impregnated with poisonous ammonium phosphates, sulphates, borax and zinc chloride that lose their potency and accelerate wood deterioration much faster than the manufacturers acknowledge.
Those owners and occupants of the over 6,000 structures not yet rebuilt from the last four years of Northern California fires should check with their insurance companies to confirm their correct interpretation of the California WUI requirements.
Companies from out of state often don’t have any idea of the construction cost differences we experience here. I researched the cost of stucco verses wood and found stucco costs to be $5 to $9.58 per square foot applied to the average new home, whereas natural wood siding installations cost is $6 to $12 per square foot on average. That doesn’t take in account the higher cost of an imperfect product, FRTW.
You have to wonder if these insurance companies are protecting their clients or paving a future liability escape. I’ve been practicing architecture long enough to see how insurance company can manipulate the markets.
He says loves shingle designed homes when they are safe and secure.