Insulating interior foundation footings
Perusing the GBA construction details, I did not see this addressed. I have an addition which calls for 3 internal posts which should have footings as they hold a significant roof load. I am in 4 ft frost depth country. I could probably avoid the question by making the wall they are in a load bearing wall which should spread the load out negating the need for any footing, but future owners are bound to cut the wall out and have the roof come down.
Also the plan is to have the floor level with the top of the foundation wall, how do people hide the interior foam once you get over a couple inches? I don’t plan on using concrete as a finished floor but it seems odd to have that foam staring at me.
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Replies
Keith, The answer to the first question depends on how comfortable you are with having load bearing elements resting on foam. If you are fine with that, use a foam with an appropriate load rating either under a thickened slab or surrounding the dropped footing on all sides. If you aren't good with the foam being under the footing, pour a pad and connect it with the slab using a pier formed with a sono tube. You will have a small area under the slab without insulation, but as a proportion of your total envelope it is insignificant.
To hide the foam at the perimeter the standard detail is to provide a ledge at the top of the foundation wall. There are a lot of variations. You can find a few of them here and at Building Science.