Replies

1. 
   krom | Mar 22, 2021 09:35am | #1

   lots of info you need to do the design here:
   https://www.ncdc.noaa.gov/climate-information/statistical-weather-and-climate-information/frost-protected-shallow-foundations

2. GBA Editor
   Kiley Jacques | Mar 22, 2021 10:38am | #2

   Hi Trevor,

   I know it is not exactly the frost-protected shallow-foundation approach you are planning, but if you haven’t seen this article by Mike Maines, I think the details would interest you. It specs 2 in. of 25 psi ESP around the footing: Minimizing Concrete in a Slab-on-Grade Home.

3. 
   Nest_Builder | Apr 11, 2021 05:11pm | #3

   Thanks!

4. 
   Nest_Builder | Apr 11, 2021 05:19pm | #4

   So the drawings do not show any insulation under the slab in a heated space. I’m Zone 5 in Putnam CT.

   R10 UNDER THE SLAB???

   It will have sleepers and ridged insulation under subfloor on top of slab but NO radiant heat.

   Thanks so much!!

   
5. Expert Member
   MALCOLM TAYLOR | Apr 11, 2021 05:32pm | #5

   James,

   There are two approaches to FPSFs. One uses the heat from the building above to ensure the ground doesn't freeze, the other uses more insulation to do the same thing. This is a comprehensive guide to both types:
   https://www.homeinnovation.com/~/media/Files/Reports/Revised-Builders-Guide-to-Frost-Protected-Shallow-Foundations.pdf

6. 
   Nest_Builder | Apr 11, 2021 05:57pm | #6

   Thanks Malcom!
   That’s what the image I posted comes from!

   But I see a lot of people saying I should have R10 under the slab and that’s what I’m finding confusing.

   If I insulate over and under the slab then it doesn’t let heat come into earth from house. That’s seems like a plus but it doesn’t fulfill the idea of the FPSF.

   But I could just pretended it was I heated and go that route...

   Thoughts?

1. Expert Member
   Deleted | Apr 11, 2021 06:42pm | #7

   Deleted

2. Expert Member
   MALCOLM TAYLOR | Apr 11, 2021 06:43pm | #8

   James,

   If you go the route of insulating the slab so that you don't rely on heat from the house keeping the earth from freezing, you are instead relying on that insulation (and that which extends out at the perimeter) keeping the warmer earth below the house from losing it's heat. The two advantages of going that route are that you save the energy you would have used heating the soil, and the house can be left without heat without suffering damage.