Extra Courses Versus Raising the Site

One good method to raise a structure high enough to prevent moisture damage is to build on high ground and/or raise the building site (building pad). This is what I’ve done on our earthbag structures so far. We spread out truckloads of road base where the building would go, drove a truck back and forth across the site in different directions to compress the soil and then repeated the process until the building site was about one foot higher than the surrounding area. The threshold and finished floor are 6 inches higher still. This should be sufficient to protect against water damage in our area.

Another way to raise the building and prevent water damage is to add extra courses of bags or tubes. But how do you fill the space under the floor, you may ask? At first this option doesn’t make sense because the work would have to be done by hand since you obviously can’t drive a truck inside the house. Once again, it’s scoria or pumice (also known as lava rock) to the rescue. These lightweight volcanic materials are rot proof, insulating and easy to work with. It’s sort of like shoveling popcorn. The work would go fairly quickly. You could speed things up by dumping truckloads of scoria or pumice inside the house before the walls got too high. Then all you’d have to do is spread out the aggregates. Spread the scoria or pumice later so you don’t have walk on it during the build. The key advantage to this approach is the added insulation under the floor, so this method is ideal for cold climates. The last step is to add and tamp soil around the exterior on a slope to direct water away from the building.

3 thoughts on “Extra Courses Versus Raising the Site”

  1. As my soil here is pure dust, and we don’t have scoria here, would it make a strong underfloor-layer to lay bags filled with foundation material flat all over the floor side by side and then tamp them? How would one then proceed from there? I don’t have any clay in my soil, so am planning a stone or tile floor, as I want to avoid the typical cement floors here. What would make a good layer between the bags and the tiles / sand stone slabs? We do have sand and murram 9which apparently is the same laterite)

    • You need a stable base under the floor. Earthbags under the floor would be lots of extra effort. It’s easier and faster to use aggregates. You should be able to build up a stable base with laterite and sand. Different aggregate sizes will lock together, fill the voids and create a fairly stable base. Then you can set the stone on top. Test it out on a small area. You may need some lime mortar to keep the stones from shifting.


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