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perimeter insulation for slab heat

Tom Sloss | Posted in General Questions on

I have 2″ rigid insulation 2′ deep around the inside perimeter of the garage. I plan to add another 2″ 5″ deep for the slab itself. My questions are:

1) do I cut the foam at a 45 at the top so the concrete fills in closer to the walls; or do I leave a 4″ foam “joint” around the inside of the garage floor? If I do cut a 45, doesn’t that remove much of the insulation around the perimeter of the slab? Or, do I just cut a 45 angle an inch or so down, so I get a skim coat to cover the top of the foam? 

2) What do I do at the door openings? I plan to have a 10′ apron in front of the doors. Where do I put the foam for this? Inside the garage seems to allow the outside cold to get under the doors; while outside may not insulate the inside from heat loss thru the walls. Do I run the foam as high as the top of the slab, or to the bottom, so the slab can extend into the apron? Do I end up with a 4″ “joint” between the slab and the apron? Would this joint break down from weather and driving over it? 

Thanks for the comments.

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Replies

  1. Steve Knapp CZ 3A Georgia | | #1

    Tom,

    Martin's basement article goes into some detail on best practices for protecting exterior foam.

    https://www.greenbuildingadvisor.com/article/how-to-insulate-a-basement-wall

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