What is the best way to stop thermal bridging between my ICF block construction walls and my footing?
An Uninsulated footing under ICF block construction walls allows thermal bridging into the concrete core of the wall allowing energy stored in the thermal mass to bleed into the soil below. This is one of the problems with building ICF on a traditional concrete strip foundation. Is there any way to stop this advantage for ICF construction from literally flowing away?
If you are looking to eliminate thermal bridging between the footing and foundation wall (as we all should), the best way to build a basement that we would suggest is to build a fully insulated raft slab first, then build ICF walls on top. See the Geo-Slab frost protected slab on grade by Legalett for more information.
Legalett slab on grade form kits provide a seamless layer of insulation below the slab an on the exposed above grade portion of the slab. This way you are insulated from below seamlessly up to the point where you would install your ICF block wall, so both are integrated perfectly.
And this is in no way a sacrifice in comfort, strength or efficiency, a raft slab design is stronger than a typical footing and slab, so it eliminates any structural cracking.
If you are looking to improve the performance futher, see Legalett’s Passive House Certified Thermalwall insulation panels designed to improve the R value and efficiency of ICF walls. Another weak spot is the door thresholds, so if you have a walkout basement you can include ThermaSill insulated door threshold forms.
If you've been through our site at all looking at foundation options then it would be no surprise that we aren't big proponets of basements, so if we were to build one, this is how we'd do it for performance and to eliminate the risk of mold. Below is a shot of what it would look like, hope that helps!
And if you're interested in the history of ICFs blocks & ICF Construction, that's here.