More on Fire Rating in Straw Bale Wall Systems

Written by Andrew Morrison

house fireThis is a response to a comment about bale buildings and their fire rating. The author of the original email challenged the fact that conventional buildings only have a twenty minute burn time and that they do not actually have a chimney affect like I describe. I disagree and you can see my response below.

Thanks for your email. What I refer to in the twenty minute burn time is the rating of the drywall. A standard wall assembly is designed to resist fire for 20 minutes and then the drywall will be burned through. Once in side the drywall, you do have chimneys, albeit small ones that run for at most 10′ and at least 8′. Fire blocking is not required until you reach ten feet in height and wood plates at 8′ or 9′ are the standard in most homes. Consider a “chimney” of 1/2″ drywall (one break in the drywall will allow the flames in), dry 2×6 studs 1 1/4″ of plaster on top of densely packed, silicone rich material with extremely low amounts of oxygen in the material. This is where the comparison is a clear winner for bale building.

The recent fire testing results support this claim. I have seen conventional homes on fire and they get out of control very quickly. In contrast, a plastered bale home will smolder for a long time before any flames actually take hold. That’s where I am coming from on this. I know it seems counter intuitive to think bale homes could last longer than conventional homes when faced with fire, but that is what I have seen and what the studies have shown. Thanks again for your email.

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