Shredded Styrofoam in Earthbags

My name is Roberta, I live in Minnesota. I am writing because I am interested in building an Insulated Earthbag house and I have a few questions. I am thinking about building a play house first to try and then a home. I have been researching lots of different building materials and ideas. I was wondering about using recycled Styrofoam, shredding it up and mixing it with cement to fill the bags. What I am hoping it that the cement will stabilize the bags. It would kind of be like Apex Blocks. They are a fairly new product that uses Styrofoam and cement compressed to foam blocks.

I am planning on laying the bags directly on top of a slab of concrete. I plan on attaching stucco netting and explanation joints as we layer the bags and applying concrete stucco to the outside and maybe the same on the inside.

From Kelly: Hi Roberta. My suggestion is to use the shredded styrofoam in the bags without any cement to get the best insulation value. Then use the bags as infill in a post and beam structure that supports the roof. This will avoid any problems with compression of the bag walls and the post and beam structure will pass the codes. There are lots of nice designs for such buildings, including those shown at The bags walls can still be plastered with embedded stucco netting, and the timber frame structure could either be kept visible on the inside or not.

From Owen: I recommend buying the Styrofoam already shredded or in small pieces. Bags of ultra-lightweight materials like Styrofoam and rice hulls need extra reinforcement to stabilize the walls. For instance, the walls need to resist wind loads. That means you’ll need to add some braces or framing between the posts. Tie the bags to the frame. This includes building strong framing around all doors and windows because lightweight bags provide no structural support (unlike regular earthbags which are very strong). The final 15” thick walls will be incredibly well insulated and save on energy bills for years to come. Building methods like this are far easier to do in low or non-code areas. Get as far away from the cities as possible to minimize costs and code barriers. Consider building in the round or hexagonal, etc. so the wind blows around the structure. Build small, keep it simple and, as always, please document your project and share with others.

Be sure to read and watch the videos about the Earthbag Scoria Casita. He shows exactly how to stabilize bag walls filled with lightweight materials.

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