Monday, January 19, 2015

Straw Bale Cat House

As mentioned in previous posts, we recently constructed a straw bale structure to serve as a temporary home for several cats. The structure is only intended to be used for a few months, until we can build the permanent building. Once the cats have been relocated to the new building we will disassemble the straw bale structure and re-use the material for other projects.

I designed the structure using SketchUp, which I've found works wonderfully for such projects. The design is very simple. The plan called for a 10' 6" x 9' footprint, which provides 45 square feet of interior space. Things didn't quite go as planned, though, but I'll get to that in a follow-up post. The plan also called for 5 courses of straw bales, providing a height of 5' 10". The roof is 7/16" OSB supported by rafters spaced 4' apart.

Since this building was intended to be temporary I did not want to go through the effort of installing a foundation. I didn't want the bales to sit on the bare ground, though. I ended up deciding to put down plastic sheeting under the first course of bales, then folded it up on the outside and across the top of the bales. This should, I hope, protect the bottom course from both ground moisture and run off.

For the next course I had to make half bales to go on either side of the opening for the door. To make pins I cut some small diameter trees (less than 1") and sharpened one end. I then drove these through the bales, into the course below, to tie everything together.

After the fourth course I placed a sheet of OSB across the end of the structure opposite the door. This serves as a make-shift loft and provides an additional 12 to 15 square feet of space. The final course of bales were then placed on top of the OSB, which helps to hold it in place.

The rafters were constructed from 12 foot long 2'x4's. I used 12' rafters to provide 18" overhangs on each side. The bottom 2'x4' of each rafter was placed across the bales at the appropriate position, and then drilled so that length of rebar could be driven through to tie them to the bales of straw. I then attached a 2 foot length of 2'x4' to one end to provide a 1:6 slope for the roof. The other 12 foot  2x4 was then attached to the top of each rafter structure, providing support for the roof.

For the roof I used sheets of 7/16" OSB. After installing the OSB I had planned to put down a layer of plastic sheeting, which would then be covered by 30lb roofing felt. Due to time constraints, though, we ended up deciding to forego the plastic and felt and simply cover the roof with a good quality tarp.

I was concerned about wind lifting the roof off of the structure, so decided to secure it to the ground with treated 2'x4's. I screwed one end to the rafter on each corner, and then attached the other end to a short length of 2'x4' which had been sharpened to a point and driven into the ground.

I still need to do some work to box in the ends of the rafters, but for now the structure is sufficient for providing the cats with shelter. I'm sure there were easier, and probably also cheaper options. Using straw bales, however, provided me a chance to experiment with using them for building. They should also all be reusable once the structure is no longer needed, at which point they will be used for mulch in the garden.

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