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Any benefit to insulating basement foundation walls?

Any benefit to insulating basement foundation walls?

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Old 08-29-17, 12:02 PM
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Any benefit to insulating basement foundation walls?

I'm having an attached garage addition built with a small mudroom providing passage into the house. The garage will be unconditioned and the mudroom will be conditioned. I will be insulating the mudroom walls down to the footing and around the perimeter of the slab with 2" rigid foam boards. Question is, is there any advantage to insulating the garage foundation walls as well considering the garage will be unconditioned space? I'm thinking it would help keep the soil underneath the structure from getting as cold as the soil outside the walls and prevent frost heave under the garage floor slab.
 
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Old 08-29-17, 12:09 PM
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I don't see any point. Insulation ultimately does nothing if there is not a source of heat or cold, as the space will eventually match the outside; the insulation just makes it take longer.
 
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Old 08-29-17, 12:13 PM
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Sure, but the garage receives sun all day long and is adjacent to a warm structure, so it seems like the insulation would at least do something. Maybe negligible. I don't know. Plus, I'll likely use a space heater when I'm working in the garage in the winter, so it couldn't hurt right?
 
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Old 08-29-17, 12:26 PM
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You changed the situation when you added the space heater, since that is a source of heat.
 
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Old 08-29-17, 04:12 PM
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The garage will still get some residual heat from the house, you would be better off insulating the walls.

Old house had attached garage with insulated walls (no ceiling) and nothing froze on shelves against the house wall. Current garage has no insulation (walls or ceiling) and I have to put all my waxes, lawn chemicals, etc in the basement because they will freeze.
 
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Old 08-30-17, 09:20 AM
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I just realized my post says "basement" foundation walls. I meant to say garage foundation walls/stem walls. What I'm asking is for the perimeter wall of the new garage, does it at least make sense to insulate vertically against the inside foundation wall in the areas that are above grade? That way I am insulating the garage slab, gravel base, and soil underneath from the cold air outside? I'll draft up a drawing and post later.
 
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Old 08-30-17, 09:33 AM
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Ideally you would use your 2" foam as the inside form for your foundation walls. You would also lay insulation on the ground under the portion of the floor that you plan to heat if it is going to be concrete floor.
 
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Old 08-30-17, 10:01 AM
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This is what I'm dealing with. Where to insulate, if anywhere? I was thinking at least against the right side wall of the garage along the inside of the stem wall so there's a thermal break between the ambient air outside and the slab. Forgot to mention the right stud wall will also be insulated (R-13 batts).
 
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Last edited by mossman; 08-30-17 at 10:46 AM.
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