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Old 01-06-2020, 11:54 AM   #1
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How to correctly insulate between floor of house built over garage slab


So I'm doing a remodel...turning an area that was a hallway and pantry and laundry area into a mudroom. The floors are out of level so I tore up the plywood and found that the first 3 feet of the entire area is built over the garage slab. So from the man door at the garage wall to about 3ft in is all over slab, this stops at the basement foundation and the remaining room sits over the basement. The flooring that sits in this area was always cold and you could always tell it was a cooler area in the house. There is wood framing between flooring and slab and the gap from floor to slab is roughly one foot. Currently they have insulation batts stapled to the joists but they obviously aren't doing much.



What's the best way to insulate between the slab and joists/subfloor to prevent any moisture issues and keep that cold air out? I don't want to create problems. I can try to attach photos once I get to working on it again.




Thanks.
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Old 01-09-2020, 07:08 AM   #2
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Re: How to correctly insulate between floor of house built over garage slab


Concrete slabs can be higher moisture. How about laying down xps foam boards on the slab and tape the seams? Then spray foam outer joints so the air is sealed under the foam boards. All area under the joists should be checked for air to enter. Foundation, wood frame sills/plates. These should be sealed and insulated as well as possible. R30 or higher all around would be best as possible. Then the heat above should keep the floor warm enough. I am suggesting conditioning the space beneath. Search and see the videos on crawl space conditioning.
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Old 01-09-2020, 07:21 AM   #3
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Re: How to correctly insulate between floor of house built over garage slab


Appreciate the input. That's somewhat where my mind was going for this. I have hot and cold copper pipes to my spigot in garage that run through the joists from the basement through that area to my garage that are not sealed around internally (but are foam sealed at garage wall), as well as hot & cold PEX lines and a 2in PVC drain. Would the holes through the joists for these 5 total pipes be enough for conditioning from a heated basement?
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Old 01-16-2020, 06:31 AM   #4
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Re: How to correctly insulate between floor of house built over garage slab


Sorry for late reply. For borrowing heat from somewhere else, I think you'd want more "holes" or open the drywall. The enclosed space can also collect moisture or such.
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Old 01-16-2020, 07:01 AM   #5
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Re: How to correctly insulate between floor of house built over garage slab


A bunch of holes will not be anywhere close to enough heat in Cleveland.

A garage slab lacks any construction measures to keep it warm, like rigid foam under and around the perimeter.

In addition to protecting the pipes you want warm floors. One approach is to bury rigid foam board vertically around the perimeter up to the house and covering the edge of the slab as deep as you can get it, below frost if possible. Then caulking the perimeter to eliminate ALL air leakage into that space.

If you go this route it can eliminate insulating the floor and allow you to condition (add heat) the space.

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Old 01-16-2020, 06:31 PM   #6
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Re: How to correctly insulate between floor of house built over garage slab


Quote:
Originally Posted by eric4985 View Post
So I'm doing a remodel...turning an area that was a hallway and pantry and laundry area into a mudroom. The floors are out of level so I tore up the plywood and found that the first 3 feet of the entire area is built over the garage slab. So from the man door at the garage wall to about 3ft in is all over slab, this stops at the basement foundation and the remaining room sits over the basement. The flooring that sits in this area was always cold and you could always tell it was a cooler area in the house. There is wood framing between flooring and slab and the gap from floor to slab is roughly one foot. Currently they have insulation batts stapled to the joists but they obviously aren't doing much.
What's the best way to insulate between the slab and joists/subfloor to prevent any moisture issues and keep that cold air out? I don't want to create problems. I can try to attach photos once I get to working on it again.
Thanks.

Is this an older home? If so, why not just level the floor and replace the other things like they have been for years and years? Some of this stuff on here if you don't know what you are doing or have little experience you can make things much, much worse.
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