garage floor insulation


Old 02-09-01, 06:20 AM
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I am in the process of converting my garage into a family room. I need to run joists on the concrete slab to raise the floor and for insulation purposes. How do you suggest I insulate this area? Do I place the insulation directly on the slab and fill the area completly with insulation then put a vapor barrier on top? I live in Wisconsin so it gets pretty damp and cold. If you have any suggestions, please let me know.

Thank you,

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Old 02-09-01, 11:25 AM
Join Date: Mar 2000
Location: Arlington, WA
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Don't put the floor joists in direct contact with the concrete. They'll rot. What you should so is remove the concrete and excavate down far enough so you can get 18" of crawl space under the floor joists. After the floor joists are in place, install kraft faced batts (R-19 or greater) between the joists, with the paper up, stapled to the top edge of each joist, then install the subfloor. And, of course you checked with your local bldg. dept. before starting this project to make sure it's legal to convert the garage to living space there, didn't you?
Old 02-12-01, 09:09 AM
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Or use the techniques used when converting basements.

Use pressure treated 2x4 glued to the concrete. Use rigid foam insulation cut to fit between the 2x. It provide insulation and mositure barrier.
Old 02-12-01, 10:03 AM
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Thanks alot for the help!
One last question. Do I install a kraft face insulation on top of the rigid foam
insul? thanks again,

Why would you put insulation on top of insulation?

Rigid Foam insulation is typically more expensive per R value than fiberglass but is less thick. Therefore foam can be used to get a higher R value in a small space.

In a basement, 2x4's are typically laid so the 4" side is down and it is only 2" tall to preserve head room. The 2x4's are laid to provide a nailing surface for the plywood subfloor. Usually pressure treated 2x4's are used to combat the potential for rot. You could put down a platic sheet first and then nail the 2x4's through the plastic into the concrete using a power nailer.

In a garage, you may have enough head room that you could use conventional joist diminsions and use batt fiberglas insulation. A lot homes you go down a step or three to get to the garage. When converting the garage, joists could be built so that the floor of the converted garage is the same height at the house floors. This assumes that the ceiling in the previous garage was high enough to allow for raising the floor.

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