Replies

1. Expert Member
   MALCOLM TAYLOR | May 11, 2021 03:01pm | #1

   Arnold,

   Any footings that don't extend down to whatever the frost depth is where you are building would require foam to insulate them against freezing.

   The other things the determine the depth of a foundation are: The thickness of the organic matter you have to remove to get down to good bearing soil, and the depth from grade to the footing to accommodate perimeter (French) drains, rock and separate pipes for downspouts.

1. 
   arnoldk | May 11, 2021 03:15pm | #2

   So exterior foam would be require or can the foam be placed on the inside as shown in my drawing?

   Thanks,
   Arnold

   
1. Expert Member
   MALCOLM TAYLOR | May 11, 2021 03:28pm | #3

   Arnold,

   Building where the frost depth is only a foot below grade, it's not something I've ever dug into very deeply. I believe the definitive guide is this one: https://www.homeinnovation.com/~/media/Files/Reports/Revised-Builders-Guide-to-Frost-Protected-Shallow-Foundations.pdf

   A couple of things I noticed on the detail you posted:
   - You show the foundation width reduced at the top. That is usually done to keep the perimeter foam under the exterior walls. Your wall is so wide that wouldn't be necessary. The foam could run up the interior of the stem-wall continuously from the footing to the top.
   - With a wall that wide, are you sure you need exterior insulation? It adds a lot of complexity for very litttle gain. Double-stud walls and exterior insulation are usually an either / or choice.

1. 
   arnoldk | May 11, 2021 03:44pm | #4

   Hi Malcolm,

   The frost line in Ottawa, Canada is around 3.5 feet below grade.

   I'll look into stream lining that interior vertical insulation on the stem wall. Doing it the way you mention would make it easier and more straight forward during construction.
   I did that thinking a shelve was required for the slab to sit on in order for the stem wall to support it.

   Thanks,
   Arnold

1. Expert Member
   MALCOLM TAYLOR | May 11, 2021 04:32pm | #5

   Arnold,

   You are better off having the whole slab over the compacted fill so any differential settlement doesn't crack it.

   I'd have loved to have lived in a house insulated like that when I was in Ottawa. Most of the ones I ended up in were extremely cold and inefficient.

2. 
   arnoldk | May 12, 2021 09:02am | #6

   Thanks for the tip Malcolm, I will definitely look into having the whole slab over the compacted fill.

   My current house is subdivision, code minimum house and it shows in the winter. The temperature fluctuation varies a lot, even the kids bedroom which are next to each other have several degrees difference.

   Thanks,
   Arnold