Planning an ICF addition.  House built into side of hill with front basement wall exposed.  The basement will actually be a garage that connects to the existing basement. See attachment.


The city inspector wants to treat the garage as unconditioned space.  As such he wants full 4' frost wall on all four sides of the garage.  My architect had planned to step the footings as they back into the hillside.  I see the inspectors point and agree that frost protection of those walls needs to be considered.  I'm wondering if there is a more elegant way to handle it.  Dirt side of the walls are protected once they get far enough below grade so it would just be a matter of protecting the garage side, right?  Would adding foam below the poured floor work?  Any suggestions?

That image was really degraded.  Let me try again.

After some more discussions we are going to frost protect the whole garage floor with 2" of foam. That way we can step the footings up and still maintain frost protection. It also minimizes how much we disturb the soil around the existing foundation wall. Seems to be good solution?

What sequence would you pour the walls and floors in? Footings first of course. Then pour the frost wall separate or do the frost wall and basement wall in one pour? The pour height would be like the first section view with a total height of 12'3" from top of footing to bottom of floor.

You can extend foam horizontally beyond the walls, creating an unheated, frost protected shallow foundation. No need to go down to 4' anywhere, just a thickened edge slab.

why isnt there any insulation on the exterior of the turn-down footer, on the vertical face, that is a huge thermal transfer, it is required under 2012IRC and IECC correct?

In the picture, the space is unheated, so no need or purpose for such vertical insulation. But if the space were heated, yes, you would add vertical foam at the right side of the Dg arrow.