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Insulating Basement with Block wall+Gap+Stone foundation

Posted: Thu Jan 10, 2019 11:53 pm
by fey
I've had a bit of trouble finding a similar situation to mine, upon which to base a decision. I will upload a diagram to hopefully clear things up, but the house is 120+ years old and built with a sandstone foundation in Ohio/Zone 5.

Half is a basement that has about 8' or so to the beams and joists, the other half is a crawl space with about 3' of clearance. Separating these two areas is a concrete block wall, stacked 11 blocks high (minus a spot you can crawl through) which leaves it a few inches from the joists. This wall then takes a 90 degree turn once it reaches the foundation wall at either end, to encompass the basement on 2 1/2 sides.

The snag for me is they also left a gap of 4-6" or so between this block wall and the foundation wall beyond it. I can't really get behind it, and I'm not sure how this factor would change how one might normally insulate it from the interior (likely R15 in rigid foam). There may be the option of taking a few blocks off the top to get more access if necessary.
basement layout.png
basement layout.png (75.85 KiB) Viewed 114 times
This is a conditioned space currently (heat only) and humidity usually hangs out around 45-50%. I'm not in a rush to do all of this but I would eventually like to encapsulate and condition the crawlspace to help the colder floors over there. I don't expect to "finish" the basement; just keep it clean, dry, and comfortable; while being mindful of how it impacts the floors above.


Re: Insulating Basement with Block wall+Gap+Stone foundation

Posted: Fri Jan 11, 2019 9:03 am
by Shannon
This is not typically what have seen but here are my thoughts:

I think for the crawl space I would turn it into a condition space and to do that I would install 2" of closed cell sprayfoam. With stone walls being so un even they are difficult attach anything to including foam insulation sheets. A vapour barrier (usually 8Mill black plastic is used around here) cover the entire floor area of the crawl space overlaying joints 24" and run up the outer walls about 6" or so and sealed to the wall foam. The ends of the "gap' where the block walls turns a 90 I would seal those spaces off at the corner with spray foam as well. Stick some rigid in there as a backer and seal with sprayfoam.The block wall dividing the areas could be framed to the ceiling and insulated as well.
This is my first thoughts on this so I would also check with local contractors who have experience with your particular set up.

Re: Insulating Basement with Block wall+Gap+Stone foundation

Posted: Fri Jan 11, 2019 11:36 am
by fey
Thank you, Shannon. Would you insulate the block walls that run along the exterior in the typical fashion, with something covering the top of the air gap?
exterior basement wall ins1.png
exterior basement wall ins1.png (31.31 KiB) Viewed 102 times
That would be prior to any batt or framing.

Somewhat similar to the thread: viewtopic.php?f=4&t=7770

Re: Insulating Basement with Block wall+Gap+Stone foundation

Posted: Fri Jan 11, 2019 6:04 pm
by Shannon
Yes I would Maybe not R15 but R5 plus insulated wall infront of it. That foam can not be left exposed in the basement however. I would need to be covered for fire protection.