Building with Straw
We are extending the existing house by about 1600 feet. We are adding
two more bedrooms, a bathroom and a multi-purpose great room where we
can have gatherings and worship times. We got the building permit
approved in October along with the electric lines and a new septic tank. The extension will be a post and beam construction with straw bale infill
walls. We've seen several building like this and they are beautiful and very
energy efficient homes to have in the desert southwest. (The 18 inch thick walls
should keep our electric bill down quite a bit!)
The first thing we had to do was cut out a section of cement so that
we could put our form right up against it. This was very slow and
tedious work. By the end of the day, we renamed the process from "cement
cutting" to cement filing".
We had to rip up the sod from our back yard and bring tons of dirt up
to level it out.
 
Our electrician, Manny, lent us a frontloader/backhoe to help with
the dirt work over the weekend. It was a huge help and saved us at least
a couple weeks worth of wheel barrel work. Unfortunately there was one
casualty from the backhoe. The freezer next to the foundation didn't
make it. :(
Here is what it looked like after a week or so of
working.
 
Since we had an existing sidewalk outside, we built a form right up
to it. We eventually added some 2x4s on top of the sidewalk since the
slab would be higher than the sidewalk.
A local Chaparral kid named Mike helped quite a bit on the foundation
dirt work.
The entire roof weight will be supported by 15 4"x6"x16' posts
planted around 5 feet in the ground and running up through the
foundation. The final ceiling height will be around 10'.
We decided to run plastic under the entire slab for protection
against moisture working up into our straw bales. The New Mexico straw
bale code requires plastic to run up from the footing between the
insulation up and over the edge of the foundation, then back. This is
why we needed the extra plastic hanging over the edge. When the cement
was dry, we'd pull it over the edge of the cement slab, then double it
back for the straw to sit on. We weren't required to run it under the
entire foundation, but we had heard it recommended as an extra deterrent
to moisture.
 
Our plans required a 4" slab on a 12" wide x 18" deep footing. This
meant that we would be wasting a lot of cement if we didn't get our dirt
built up around the inner edge of the footing. Since the dirt was so
loose and we hadn't packed it ahead of time, we had to build a moveable
inner form to sure up the inside edge of the dirt before we put down the
plastic. We couldn't get the nice inside edge without an inner form at
this point. (Hind site told us we probably should have packed all the
dirt into the outer form, then dug out the 12"x18" footing.) To work
forward from where we were, we took two sets of 2"x12"x10's and held
them together with 2 2"x4"s sticking down into the ground about 6
inches. Then we wedged a couple of pieces of extra 2"x4"s between the
inner form and outer form for bracing. We filled in the extra dirt,
packed it and wet it and then pulled away the form to do the next area.
Since we had two 10' long forms, we could do 20' at a time. It took 3 of
us about a day and a half to get it looking good, and we only had some
minor amounts of dirt fall back into the trench. The cement guys
estimated that we saved around $700 in cement by firming up the corners
this way and not wasting any extra cement.
 
We weren't really sure what the best way was to tie in the posts to
the foundation. We had bent the rebar around the corners then built
boxes around posts with additional rebar. We then tied the boxes for
each post into the rebar in the footing.
 
Since the posts were so deep, we only had to brace a few of them with
2x4s. As they poured the cement we just made sure they were still level.
 
We had a local team of cement guys do our cement pouring. We turned
out using 33 yards of cement at around $59 a yard plus $900 in labor.
Considering none of us had any tools or skills at cement pouring, this
seemed like a great bargain.
After the cement began to dry, we put in rebar spikes about 18 inches
apart. These will help the first layer of straw bales remain firmly
locked into place. Here is what it looks like now that it is dry:
 
We'll soon be moving on to framing our addition and will have some updates as
we move along.
If you are interested in helping or would like to see how we've put
our plans together, or just want to hear how things are going, contact
the
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