Hi - Build in Scotland onto rock. Balancing costly digging out of a very stable surface with the height addition of an ICF raft type foundation. My understanding is ICF raft completely isolates the concrete from 'cold'. Potential engineer is recommending strip foundations and ground bearing slab within. Looks OK and simpler to execute, less height and poured foundations easier on uneven rock of differing solidity. However it means that the concrete inside the ICF walls will sit on the concrete of the strip foundations. Waterproofing in concrete will sort damp issues but my perception is that it is a cold bridge - does it matter for what is a small area in comparison to the total footprint.......any ideas? Anyone know of strip foundations where ICF internal concrete is thermally isolated from the ground?

Question, what's stopping you from merely incorporating insulation under/around strip footings to thermally isolate them?

You're going to have to perform waterproofing on the the ICF walls anyhow. Mating an EPS box for the foundatins shouldn't be terrifically hard.

Also, recent video one one method of waterproofing ICF.

https://youtu.be/_hBfFHPvb9I

Hi,
yes waterproof as per the video .but i i don,t see the problem -any cold will only come up into the wall and that is insulated both sides and when you lay your floor you will be no doubt using underfloor and first stage in that is an insulating layer below which the piping fits into .
and anyway if it is really bedrock that will be being heated by the ground from below --temp of ground all year round in scotland at 1.5m is between 10-12c--so it could cold /hot bridge and warm the wall up in the winter .thats how ground source heating works
only time I have heard of something like you describe is on very soft/wet ground that is liable to freeze in winter and melt in summer --permofrost --then they just make a raft of 1msq blocks of polystrene below concrete foundation raft --bit over kill for scotland LOl
you are over thinking it a bit I feel --

Thanks - very helpful for points to raise with the engineer....

On the Canadian Shield we have placed ICF directly on the surface of the granite rock, doweled in with rebar to hold in place, no footing required - did this in earthquake prone California as well with great success

Thanks Chris - nice idea