We (South Brent CLT, Devon, UK) are planning to build 14 affordable homes using Straw Bale wrap around a Douglas fir frame. We want to use as little concrete as we can, but, we will have to have a structural floor slab and sump for the Radon Gas on Dartmoor above the sub base and DPM to satisfy Buildings Control. I believe we will then only need pile foundations where the posts meet the slab rather than a ring wall foundation around the whole footprint. Can anyone advise us if we can use a Cob or Rammed Earth Screed with water pipe underfloor heating in it to save the top 50-100mm being concrete as well?