Foundation insulation retrofit for addition
We have a 1950’s single-story house in northern New Hampshire (climate zone 6). It’s a simple rectangle of ~1000sqft with an unfinished basement. A mudroom (150sqft) comes off one side, and provides the main entrance into the house and the only stairs to the basement. It is concrete and the foundation edges may be >8′ depth, since the steps lead all the way to the basement, though the entryway area is a slab.
So, how do we mitigate heat loss from the uninsulated and exposed concrete foundation of the mudroom and steps to the basement?
I’m concerned that insulating the exterior wouldn’t be effective, unless we did the entire house, because the main house foundation is going to be insulated on the inside, and the adjoining concrete would create a thermal bridge. But let me know if you think otherwise.
I’m tempted to go with insulating the interior with EPS under plywood as per https://www.greenbuildingadvisor.com/article/installing-rigid-foam-concrete-slab. But if we do that, how do we handle the steps? Is it possible/practical to run foam and plywood over each step? I can’t find guidance/details on this, to create both insulated and solid steps. We would have to raise the doors – but that’s fine, we’re planning to replace them and have the headroom.
Would appreciate any insights.
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