CAROLYN'S BLOG ABOUT THE HOUSE CONSTRUCTION
AND THE YEARS BEYOND
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Sun, Apr 17
6:00 am

How Strong is a Straw Bale House?: I watch the comments on You Tube to decide what to blog about and the comments lately have been about how strong and earthquake-resistant a straw bale house would be. I certainly understand everyone's earthquake concerns. It seems as if people also are wondering if someone could dig through the walls or drive a car into the house and destroy it. I'm not sure where those concerns are coming from, but I will talk about the strength of a straw bale house today.

The bales that I used are three-string bales and they are 2' x 4'x 4' and weigh about 90 pounds each. If you have ever tried to pick up a three-string bale, you will understand. In the wall-raising photos, you won't see anyone tossing one of these bales around by themselves. It took at least two people to lift one, so if you have the idea that straw is light, go find a three-string bale in a feed store and try to lift it up. (some states have smaller, lighter two-string bales) My house has 200 bales, so that comes to 18,000 pounds or 9 tons of weight in the walls, if they each weight 90 pounds and I never did put one on the scale. But it's somewhere in that range. If a house is made of the smaller bales, it would have more of them. To hold up the walls, I have a two-foot foundation and stemwall. Most houses only have a foundation that is a few inches wide, because their walls or only as wide as 2 x 4's or 2 x 6's.

Then, I have a couple truckloads of clay soil, mixed with water and chopped straw covering both sides of the bales. I think it is easily another ton of weight. Those earthen plasters dry very, very hard. I recently decided to recover the house with lime, so I got out a wire brush to roughen the surface of the plasters. It was hard to scrape, even with the wire bristles! Most people cover the house with stucco wire and then a thick coat of stucco. On the inside, I think they have drywall mud and/ or stucco. Many regular houses have a layer of foam board and chickenwire on the outside and then drywall on the inside. Stucco is blown in a thin layer over the chickenwire. Other houses are stacked concrete bricks with metal rods for support.

I am not an earthquake expert, because we don't have that issue in the Sonoran desert and I hope we never do! The areas that are prone to earthquakes have building codes that reflect this and California has earthquake-resistant strawbale codes. I believe they require the house to be post and beam, where the straw is essentially insulation, but it does not support the roof as in my house. The posts and beams have diagonal bracing. I'm sure there is more to it, also. The website of the California Straw Bale Association is here: http://www.strawbuilding.org/

In terms of someone driving a car into my wall and whether it will knock down the house - I guess that's about the same as a hurricane hitting - high winds. One of the things I like about this house, is that straw is flexible. It is not brittle like concrete and brick, so if something did make the house move, the straw would allow that to happen without breaking. As we built the house, we put metal rebar rods down through the straw to hold them together, so they won't slip or slide against each other if some force makes one of the move. We also put metal lath against the wooden window and door bucks, than then fastened into the bales, so the bales won't slide against the wood, either. Then, we put one long metal rod of all-thread that goes from the foundation all the way up to the roof trusses. This gives more strength. I noticed that the walls moved in the wind until we put the top plate on and fastened the all-thread. Then, there was no movement. I feel this house could handle a small earthquake because the straw has this flexibility, but the plasters would crack. Again, that is my feeling and nothing I have studied.

After living in this house for ten years and through some very strong thunderstorms, I have never felt the least shudder in these walls. The others I know with straw bale houses will say the same thing. This is one really solid, strong house! It may be partially because it is small, so it has all the bracing of the side walls, also. But I think it's mostly because the walls are incredibly strong. We laugh at big bad wolf jokes around here.

If you have other questions - send me an email - strawlady@comcast.net.

Keep it Simple - and be kind!
Carolyn