Strong is a Straw Bale House?: I watch the comments
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
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.
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/
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.
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
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