Exterior and interior foundation insulation crossover
Chris_King| Posted inEnergy Efficiency and Durabilityon
Hey All,
In the process of adding exterior insulation to foundation wall but am having an issue in a spot in the backyard where there is a new patio and front yard with a deck. My wife would rather i not rip out a brand new patio and new deck to insulate the foundation. So i was wondering if it would be better then nothing to in those areas put the insulation on the interior of the block and just have an overlap of say 10 feet where there is both exterior and interior insulation?
Thanks,
Chris
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Replies
Chris,
Yes, that would be better than nothing.
Even better would be to put 100% of your basement insulation on the interior, or 100% of your basement insulation on the exterior.
The problem, as you apparently realize, is that you have an unavoidable thermal bridge when you switch from exterior to interior insulation.
The R-value of concrete is somewhere around 1 per foot. So 10 feet of concrete, where you have the insulation overlapping, has an R-value of about 10. That's not a full analysis of the 2D heat flow but it's enough to indicate that you are on the right track doing about that much overlap.