Interior Face Frost Protection Depth for Unheated Space

[ForestStructural]

I have a project on a sloping lot where the rear foundation wall is about 6' higher than the front wall due to a sloping site. The ground level space is an unheated garage and the foundation guy is suggesting that the bottom of footing needs to be 4' below the INTERIOR/SLAB elevation which would make the total wall about 10' high. In my mind the building only needs frost protection on the exterior side and the footing can be placed just below the interior slab (i.e. a 6' high foundation wall at the rear). Thoughts?

 

[BAretired]

The inside of the garage will be subjected to the same temperature as the outside, so if you want to avoid frost heave, provide sufficient depth of soil or its equivalent in insulation.

 

[dik]

I'd likely put insulation on the outside face of the basement wall, and DOW Hi 60 under the footing and extend out 4'.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[ForestStructural]

Got it, thank you, I hate to get too cute with this but what if I were to insulate the interior edge of the foundation wall and footing (i.e. shallow frost protect the interior and only extend it 12"-16" below grade)?

 

[CarlB]

Your scheme leaves some cold bridges from the inside cold temperatures, to the footing. The below additional insulation could address that. Though the slab itself could experience frost effects.

 

[Brad805]

Stepped footings and increased wall heights are incredibly common for this situation.