Fire Testing Straw Bale Wall Systems: They Pass!!

Written by Andrew Morrison


house survives fireI received an email today from Bill Christensen, the proprietor of It holds some very exciting news on recent fire testing of straw bale wall assemblies. Of course, those of us building straw bale houses have known that they are extremely resistant to fire; however, now we have proof to back it up! Here is what Bill had to say:

“It’s my pleasure to announce that plastered straw bale walls have just passed two important fire tests.

Two walls were constructed at a building materials testing lab in San Antonio earlier this summer – one was built with poly-tied bales on edge and covered with two coats of hand-troweled cement/lime plaster over stucco mesh, intended to approximate an infill wall in a commercial or institutional (or residential) setting. The second wall was stacked flat, put under 600 pound per linear foot load, and shot with two coats of clay plaster, approximating load bearing residential construction. No mesh was used on this wall.

The cement/lime plastered wall easily passed the ASTM E-119 2-hour fire and hose stream test. Lab personnel told us they felt it probably would have made another hour easily.

Due to some cracking on the exterior (non-fire) side of the clay plastered wall which occurred while moving the wall up to the furnace, and having seen the fire side plaster on the cement/lime wall basically being held on only by the wire mesh for the majority of the second hour, and considering that a 2 hour rating is rarely required for residential construction, we chose to do the clay plastered wall for just a one hour test. It too passed.

The official test reports will be available in about two weeks on the and websites. They will also be included in the appendix of Bruce King’s forthcoming book, ‘Design of Plastered Straw Bale Structures’ (due out in time for the ISBBC in Ontario in late September).

Next time some insurance company gives you a hard time about straw bale being a fire hazard, you have an answer for them.

Congrats to the team: Bruce King, David Eisenberg, Matts Myrhman, Ben Obregon, Frank Meyer, Kindra Welsh, Baron Cougar, Mike Atkinson, Paul Taylor, and yours truly.

Thanks also to CASBA, COSBA, SBAT, and the individual donors for their financial contributions, as well as to whatever foundation it was that Bruce King managed to get the grant from.”

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6 Responses

  1. At 8:07 AM, Eric Webber said…

    Can you tell me more about how this test is run? Is this a standardized test that all wall assemblies have to go through for fire testing? Thanks.

  2. At 8:13 AM, Andrew Morrison said…

    The test used was the basic fire wall test used on any wall assembly that requires fire testing. In most residential applications, this is limited to a 20 minute fire wall (standard drywall assembly); however, 2 hour fire walls are required between living units of multiple family houses and in some commercial applications. You can learn more about the test by clicking the following link. I hope that helps.

  3. Did they explore a typical orgination of a fire from an ectrical outlet or light switch that creates a spark and ignites the hay within the interior of the wall.

  4. Hi Vince. The testing they used was the ASTM standard test for fires in wall assemblies. There is no way for flame spread to take place from an arcing electrical circuit because of the extreme density of the walls.At worst, the arc would sustain some smoldering until the electrical circuit dies and then the fire would either go out or slow smolder. It would be much safer than in a conventional wall where such events happen in a “chimney” otherwise known as stud bays.

  5. I looked for the test report on the site listed ( but they are apparently not in business any more. My insurance agent is interested in getting a copy of this test report to help with our insurance bill for our straw bale house. Is there another place to obtain a copy of the test report?

  6. Hi Jim. I visited the site today and still find that it is active. I suggest you try contacting Bruce and/or Sarah at [email protected] and [email protected] to see if they can help you navigate the site. It seems to be based on searching for data documents these days and I suppose you’d need to know exactly what you’re searching for. It’s a bit cumbersome, but I think with their help you will find what you need.

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