One of the many things we have to work out is how to insulate the ground floor. The Architects Matt and Elly, are helping unpick the mysteries of what you usually take for granted since it’s buried in the ground. It’s all a balance between making sure the building doesn’t sink, cost, achieving un-interrupted insulation, minimal thermal bridges, and it turns out dealing with radioactive gas.
We’re going big on fabric-first to minimise the heating required to be comfortable, and this very much relies on deep levels of unbroken insulation around the entire building envelope – including all those tricky connections between roof, walls, and ground floor. Think onesie, but building sized.
The more we insulate the walls and floor of our home (and we will be, a lot), the more heat will want to try to escape from any thermal bridges at the wall-floor junction, also increasing the risk of condensation and mould growth here. So insulating this junction becomes crucial. A popular solution for passive house buildings is to use insulated raft-type foundations where the concrete slab is poured into a ‘bowl’ or ‘tub’ of insulation that surrounds it entirely, insulating it from direct contact with the ground. The edges of this ‘tub’ of insulation are usually continuous with the wall insulation, and so much the better for avoiding thermal bridges in the foundations. This is the plan for the Tin and Stone barns.
However, it’s not that straightforward for the Stables – short of lifting up the entire building, it’s going to be hard to retrofit an insulated foundation system. Instead we need to dig down to bedrock, pump in the concrete and then insulation will go on top. Some clever calculations are required to avoid the risk of condensation and we also need to keep the load-bearing structures in place whilst the floor gets ripped up. At least digging everything out will be easy because the stable floor is mostly cow poo.