Foundations
Lime Sublime - This article is part of a series.
My foundation design was inspired by this figure from The Hempcrete Book (Stanwix & Sparrow, 2014):
Inspiration for my foundation design
I didn’t do everything in the figure. Just the idea of a stem wall (plinth) with hempcrete continuing down behind it. A stem wall protects the hempcrete and lime render from splashing and flooding.
My actual foundation (and floor) design
I started by setting out the site and laying concrete blocks for the outer layer of the foundation. (The concrete blocks were left over from my house build.)
Later I filled the concrete blocks with perlite, for insulation.
Drainage is important for any building. My site had some slope to it which helps. When I was digging it out, I unearthed a long-lost storm drain! Perfect: runoff from the roof can drain straight into it.
Once the outer blocks were laid, I set up formwork and rebar to pour the inner concrete layer. This is where the timber frame will sit. I also laid a course of bricks on top of the blocks to reach the final height of the stem wall.
The damp-proof course I used was “Aldamp” 450mm x 10m. It is bitumen-coated aluminium. Nice and malleable. It is here to prevent ground moisture from wicking up into the timber frame and hempcrete wall.
I also put 30mm of XPS rigid foam insulation around the inner edges of the foundation. This is an unusual choice: normally it would be placed on the outside edge of a concrete slab. But as it was added as an afterthought, this was an easier option.
