(This post is a précis of a post and thread discussions that took place on the eBuild forum October last year and subsequent discussions with my builder.)   Many of the self-builders active on the forum will have used or be familiar with the Passive Foundation system marketed by MBC Timberframe.  The essence of this is that the foundation is a raft slab that incorporates a ring-beam that sits inside an EPS former.  This former both acts as shuttering for the concrete pour and as insula