Radiant floor insulation with a frost protected foundation
mbessearchitect
| Posted in Energy Efficiency and Durability on
Anybody have experience with radiant slab heating a frost-protected shallow foundation in climate zone 5 or greater? Should the underslab insulation be reduced at the perimeter to allow heat to protect the frost-protected foundation?
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Replies
I am in central Ohio and used the WarmForms and lots of EPS for my slab ( 6" on vertical edge, 4" for about 2 feet on thickened edge of the slab and 12" under the rest of the slab). We do not have or need radiant floor heating with this configuration. The floor never feels hot or cold, even after exiting the shower. Now, if you are going with substantially lower insulation levels, perhaps the radiant heating would be welcome.
Steve Young
It depends on how you design your FPSF. There was recently a good discussion on this topic. I'm not very good at searching and linking articles here yet, but I'm sure Martin will chime in soon.
The bottom line is that there is prescriptive method for designing FPSF in the IRC. That method relies on heat from the house to help protect the foundation, and it requires little or no floor insulation. There is a Builder's Guide to FPSF that provides alternate design methods, including those that do not require any heat from the building.
If you follow those guidelines, you are free to insulate as much as you wish under the slab. https://www.homeinnovation.com/~/media/Files/Reports/Revised-Builders-Guide-to-Frost-Protected-Shallow-Foundations.pdf