Based in Berkeley, Calif., and recently celebrating 20 years in practice, Arkin Tilt Architects is dedicated to sustainable design and construction. The husband-and-wife team of David Arkin, AIA and LEED AP, and Anni Tilt, AIA, live and breathe responsible residential design, and their clients in the bay area and beyond come to them primed for their thoughtful approach. David’s training includes work for sustainable design pioneers Sim Van der Ryn and Obie Bowman, FAIA, and Anni, who also has a degree in civil engineering in addition to her M.Arch, worked at Fernau and Hartman Architects, also leaders in ecological design. Over the years, their research into materials and methods has deepened their dedication to straw-bale construction. After the California wine country firestorm hit last October, resulting in 44 deaths and more than $9 billion in damage in Sonoma and Napa counties, David and Anni were particularly anxious to learn how the many straw-bale houses and outbuildings they designed for the area had fared.

They’re happy to report that their projects performed very well, despite the extremely adverse conditions. Not satisfied with just the survival of the buildings, they’ve made it a priority to learn where weaknesses and vulnerabilities occurred so they may address them going forward—in repairs, rebuilds, and new construction.

What’s more, with permission from their clients, they’ve made eight straw-bale house plan sets available free of charge to those who lost homes in the fire, complete with structural calculations donated by their office mate, Kevin Donahue Structural Engineers. Those plans can be found on the website strawbaleplans.com

RD: David, the information you’ve been accumulating about the fire damage has a purpose beyond the firm’s education, yes?

DA: Yes. I’m a founder and the current director of the California Straw Building Association (CASBA). Anni and I have just come back from the Rocky Mountain Natural Building Conference, organized by the Colorado Straw Bale Association. Everyone was very interested to hear how buildings survived the fire. Insurers were especially interested, as some can’t currently underwrite straw-bale policies. We finally have a code for straw-bale construction from the International Code Council, which is helping. So, in my role as the CASBA director, I’m collecting anecdotal information. We’re doing a survey of sorts.

What are your findings so far?

DA: We’ve done probably 20 to 30 projects in Sonoma, Napa, and Mendocino, along with a few more remodels to help family out. A good number were directly in line with the wildfires or at the boundaries. Nearly all of our projects survived. Yay, straw bale!

It’s not a guaranteed, of course. You still need sturdy wood frames, metal roofs, and good fortune. In some firestorm areas, the best building wouldn’t survive.

Where we did see damage, it was because of some element apart from the straw-bale walls. For instance, on the Rosenberg/Zuckerman project, there was a wood barn door close to the ground. It caught on fire. Going forward, we’re going to pay extra careful attention to what is at the base of the buildings, close to the ground. We saw that patios and porches made a difference, especially patios that run further out beyond the porch columns.

The Rosenberg/Zuckerman house is shown before and after the fire. Photo: Ed Caldwell
Above: Arkin Tilt’s plaster supplier noted that the pink hue on the walls is from the fire heat drawing out the natural iron oxides. The soot brushes off. Photo: Michel Couvreaux

AT: We found that with heavy timber, redwood did better than Douglas fir. Redwood is more fire resistant.

DA: We early on did a PISE house up in wine country. That’s David Easton’s term for rammed-earth construction [builder/consultant David Easton of Rammed Earth Works]. It was 18 inches of solid PISE. Today, our energy code would not let us do that; we would do it with a thermal break and use straw bales…At any rate, the wood frame caught on fire, but not  the walls.

AT: On the PISE house, we used a wood cribbing detail. It was so beautiful with light coming through, but it was not good for fire. How fireproof your exterior walls are is another piece of the puzzle. Any exposed wood can be a problem. So, we’re looking at cement board for a project we’re doing in Nevada, and we’re looking at metal siding. The devil is in the details of the whole picture. You have to watch your eave vents, so we’re looking at eave products with intumescent coatings, like Vulcan. You have to make the soffit of non-combustible materials. It seems from the evidence of the fire, those kinds of details can make a difference. We’re already designing for State of California Chapter 7 for Wildland Urban Interface standards, but you have to go further than that.

DA: A Class A roof makes a big difference, too. Our go-to for roofs is metal, and we’ve already seen that metal roofing can help a lot. There are lots of tools in the tool box.

Along with insurance industry concerns about straw bale, there appears to be a misconception among the lay public and even firefighters that it’s more vulnerable to fire than conventional building materials. Why is that?

DA: Most people don’t understand there are certain assemblies of straw-bale plaster walls that even exceed code. There is one assembly with lime plaster and bales stacked on edge that can last 2 hours, according to ASTM testing, and another for clay plaster in bales laid flat than can last an hour. Most residential doesn’t usually achieve an hour.

Some people complain that when fire reaches the straw-bale walls, they smolder. But when the bales are densely packed, the flame-spread index and smoke-developed index is within the limits. If you’ve ever thrown a phone book into a fire, it takes a long time for the oxygen to get through the densely packed pages. It takes a long time to burn.

AT: Also the plaster really does slow down the fire by keeping the oxygen out. We did a straw bale studio and the roof burned, but the finish on the walls remained intact. Another aspect that’s interesting is that you don’t have the structure collapse when there’s a fire.

The effort to rebuild in wine country will be huge, especially for a region that already saw shortages of skilled labor. You’ve made straw-bale house plans available to people who’ve lost houses to the fire, to help speed up the recovery. What else is a priority for the firm?

AT: Although people want to rebuild quickly, and counties are helping, we want to do it in as healthy and as low-carbon a way as possible. And we’re part of a group working on that. We’d like to see more net-zero construction to replace what’s gone. We’d like to see more accessory dwelling units on individual lots to help alleviate housing shortages and affordability issues.

DA: Building smaller is another opportunity. We had a fellow who contacted us and would like to replace 2,400 square feet. But if we can get all that livability in 1,800, why not do that?

Beyond the architecture and the building, you have to extend thought and care into the landscape. They can work together to give you a better chance for survival. When the fires come again—and they will come again, wouldn’t it be great if more houses survived?

AT: It’s not that we didn’t think about fire before—we did—but it’s amplified the consideration. Not just in California, but everywhere through the West. And yet, we still have to make sure that we create something that’s livable—we can’t just build fortresses.