Day 73: The Earth might shake, but that straw bale home is gonna hold its ground

On the very day a deadly earthquake struck Italy, new research was unveiled that could help people survive such tragedies.

Darcey Donovan directs tests of the straw bale homes she's been building for poor residents of earthquake-prone regions in the Middle East. Credit: Mike Wolterbeek, University of Nevada, Reno

Civil engineer Darcey Donovan, a graduate of the University of Nevada at Reno, has been building straw bale homes since 2006 in the foothills of the Himalayas — where 100,000 people died in a 2005 quake. Her homes are affordable, made from locally available materials, and much more energy efficient than conventional houses. And now, she reports that they can withstand earthquakes too.

A full-scale, 14-by-14-foot straw house, complete with gravel foundation and clay plaster walls, was subjected to double the force recorded at the 1994 Northridge, California earthquake, the largest measured ground acceleration in the world. The house shook and swayed violently, cracked at the seams and sent out a small cloud of dust and straw … and remained standing. 

“I am extremely pleased,” Donovan said in a short video about the tests. “The building is intact; nobody would have been killed.”  The full University of Nevada press release is here. 

I immediately thought of Ed Dunn, a green builder who has designed or constructed 30 straw bale homes since the mid-1990s in Flagstaff, Arizona (where I lived for 10 years). Okay, so they can withstand earthquakes, I asked him. But what about the sorts of weather Flagstaff sees: the temperature extremes, snow, wind, and hard summer rains? The rest of the post recaps his responses.

They're functional -- and they look great! This isn't an Ed Dunn home. This photo was taken from treehugger.com. Credit: Ted Owens

Q. Can you remind me why straw bale homes work so well in Flagstaff’s climate?

Dunn: Straw makes great insulation. Two foot thick walls give an R value (resistance to heat loss) of 33. Compare that to conventional R19 walls (which are actually R 12 as a system). The straw is more continuous without the thermal bridging found in wood stud walls so they are more effective in holding heat in the house. It has been shown to work extremely well with passive solar designs.

Q. Of the homes you’ve built, how many have fared well through storms, snow, winds, etc. long enough that you can be pretty sure they’re withstanding the test of time?

Credit: Ted Owens, treehugger.com

Dunn: None have reported problems with storms as we build them with “good shoes” (foundation keeps bales away from the ground), “a good coat” (lime or portland cement stucco on the outside), and a “good hat” (metal roofs with a two foot overhang). We usually install gutters to prevent water splashing up on the exterior walls. Many of my clients collect water off the roof anyway.

The above answers came in an email. In a follow-up phone call, Dunn added that he “was not surprised by this [earthquake] study at all. In fact, he thinks straw bale construction rivals the strength of conventional framed homes.

“You can walk into a framed house and shake it, and the whole thing will move. Once you put the sheeting on, the house becomes very solid,” he said. “With a straw bale house, once those bales are installed, the house becomes solid. I’d always wanted to see how they perform in an earthquake.”

He said his “good shoes, good coat, good hat” motto is actually an old English saying. “You have to build consciously and attend to those kind of details no matter what kind of structure you’re building,” he said.

Ed Dunn’s Web site is here.