How to Build in Fire Zones: Learning From Australia

It can be done, but it's more expensive.

House burning in Napa, 18 August 2020
House burning in Napa, 18 August 2020.

 Justin Sullivan/Getty Images

As fires rage on in California, a lot of people are again wondering why people are living in these fire-prone areas and why their homes are not more fire-resistant. Author Anthony Townsend asks:

In many ways, architects are the wrong people to ask about this; the problems in California are a lot bigger than the building codes. Writing in the Atlantic after 2019's fires in California, Annie Lowrie noted that many people moved to the "wildland-urban interface"(WIU) because that was where they could afford to live.

Wildfires and lack of affordable housing—these are two of the most visible and urgent crises facing California, raising the question of whether the country’s dreamiest, most optimistic state is fast becoming unlivable. Climate change is turning it into a tinderbox; the soaring cost of living is forcing even wealthy families into financial precarity. And, in some ways, the two crises are one: The housing crunch in urban centers has pushed construction to cheaper, more peripheral areas, where wildfire risk is greater.

After the 2019 fires, I asked Anna Cumming, the editor of the Australian green shelter magazine Sanctuary (which I once described as "the best green shelter magazine available anywhere" and it still is) about Australian codes. After 2009's "Black Saturday" they introduced Bushfire Attack Level (BAL) ratings. Building designer Dick Clarke wrote in Sanctuary recently about how this has worked out:

To establish a site’s BAL rating, land was surveyed by the various state authorities and classified as ‘bushfire prone’ or not, with the exception of most farmland. The ratings range from BAL-Low, where the risk is considered nominal, up through various radiant heat loadings BAL-12.5, 19, 29 and 40, to the highest hazard being FZ, flame zone. The radiant heat number is estimated in kilowatts per square metre (kW/m2), at various prescribed separation distances, with flame zone assuming that exposure is above 40kW/m2.

Evidently "the experience on the ground is that the impact of the standard has been huge." One of the biggest changes was with windows and doors, which now needed to have a 30-minute fire rating in the FZ zone. This gets expensive: "One modest house in the Blue Mountains near Sydney faced a cost for windows and doors that increased from about $60,000 for BAL-40 windows to nearly $300,000 for BAL-FZ. Needless to say, the young couple’s dreams were shattered and they sold the land."

Site planning is also important, with fire authorities approving the site plan and with trees cleared directly around the house. Then there is the house form itself, which can affect how easily the house burns:

Simple shapes are best as they allow the smoothest flow of wind – and the embers born on it – over and around the house. This minimises the build-up of embers in corners where they are at greater risk of causing ignition. Roofs that have no valley gutters are a much better idea than complex roof shapes; box gutters should also be avoided. Smooth materials and simple detailing are also advisable. 

Then there are fire suppression systems, water tanks, engine driven pumps that work when the power is off, sized to run for an hour, "long enough to meet an ember shower descending ahead of the approaching fire front, for the five or 10 minutes the front takes to pass, and then for another thirty minutes to extinguish any residual embers."

Meanwhile, Back in California...

In 2008 a set of regulations known as Chapter 7A was introduced that set standards for roofing, siding, windows, and decks for houses built after 2008 in fire zones. According to Dale Kasler in the Sacramento Bee:

Experts said the regulations seem to be particularly effective at protecting structures from the types of wildfires that are increasingly common in California, where wind gusts can blow embers a mile or two ahead of the main wall of flames and do some of the worst damage.'A window breaks, a vent breaks, the fire gets into your home and you’ve got an interior structure fire,' said Joe Poire, the city of Santa Barbara’s fire marshal.

But it is not applied everywhere; even in communities that burned to the ground, builders are not required to build to the standard. Developers don't want to pay the cost and buyers don't either, so they make deals with the local politicians. "Local governments have the discretion of rejecting the Cal Fire designation ... some city councils have been squeamish about the state’s maps because of fears that the Chapter 7A code will inflate construction costs, or for other reasons."

The building code requirements for meeting 7A and building in the WUI are not exactly dire; non-combustible cladding and roofing, a few details to prevent embers from getting in, treated lumber for exterior decking. Looking at windows, they must be "insulated glass with a minimum of 1 tempered pane or 20 min rated" – not exactly the $60,000 or $300,000 extra cost that we read about in Australia. But even this is too much for some California builders and politicians.

So, circling back to Anthony Townsend's question, there is a lot architects can do, but these houses are rarely designed by architects in North America. And as he also notes, cost and politics matter; even the relatively minimal requirements of Chapter 7A are not applied evenly. People are moving to the WUI because that's about the only place they can afford to live. This isn't a design problem; it is fundamentally an economic one.

On the Whole, I Would Rather Be in Australia

Merimbula Lake House, Strine Environments
Merimbula Lake House, Strine Environments.  via Sanctuary Magazine

Every time I show these wonderful homes and buildings from Sanctuary, I am reminded by Australians like Treehugger Emeritus Warren McLaren that the country has massive suburban sprawl and lots of horrible quality housing. I wrote earlier: "I know Australia isn't perfect, that there are fires and poisonous bugs and Tony Abbott and they make you wear bicycle helmets in the heat, but the houses!!!" Cumming (Sanctuary's editor) sent us some links about beautiful, fire-safe houses:

"An uplifting prospect" – An exceptional block of land calls for a special kind of home.

"Shipshape Retreat" – Working with a modest budget, architect Matt Elkan transforms four salvaged shipping containers into a stylish, low-maintenance getaway.

"Future Focused" – Made of strawbale, recycled tyres and earth, this owner-builder project has paved the way to a whole new career.