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Insulation under raised house

Posted by neworleans (My Page) on
Sat, Apr 26, 08 at 8:00

Need help in determining what is the best and cheapest way to insulate under house I've been told foam roofing tar and attic insulation


Follow-Up Postings:

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RE: Insulation under raised house

Is this a crawl space or exposed

Here is a link that might be useful: Air Conditioning Repair made Easy


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RE: Insulation under raised house

This is an exposed area about 1,500sq ft.


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RE: Insulation under raised house

I think I caught this in home repair??

I don't know what you mean by attic insulation and foam roofing tar.

do you plan to insulate with batt insulation and use a felt paper attached to the underside of the floor joist?

I often hear felt paper called tar paper. Is this what you are talking about?


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RE: Insulation under raised house

Yes felt paper but what Iam saying is that spray foam can be used to insulate the same way as your walls but I find that to be expensive and roofing tar as a sealer to be brushed or sprayed on if possible I want to know what can be the best fix at a reasonable price and not cause more problems.


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RE: Insulation under raised house

there are many ways to insulate raised floors.
But for it to be effective you need to stop air leakage
from the crawl space to the living space, insulate the
floor and then stop air movement through the insulation
from the crawlspace.
When air moves over or through insulation it robs it of
its insulating value.
One method is to foam...it seales the leakage at the floor,
adds an insulating value and stops air movement through the insulation.It really does 3 jobs in one.
To save cost, you add labor.
Someone to prep the floor prior to insulation, caulking of wire penetrations, oversized holes under tubs, plumbing penetrations, etc.
Then the install of the insulation of choice..I'll use batt insulation in this example. Once batts are installed correctly..meaning well fitted, not compressed, no gaps..then an air barrier should be added to stop the air movement across the insulation.
I generally recommend foam board..nailed with button cap nails to the undersides of the floor joists. Caulk foam board around perimeter of house, tape all seams for an air tight seal.

I have seen batts with tyvek, batts with felt paper, but the only install I have done besides spray foam is the one I described above. This under floor install is about the only time I recommend foam..it is just too_costly for the average home owner, add extended payback..it is just not cost effective. But in sealing floors..foam is the easiest install.

best of luck


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RE: Insulation under raised house

My floors hav already been installed and I do have insulation between floor and plywood but I think you have given me a fix for the problem thanks.


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RE: Insulation under raised house

It would be a good idea to consult with an engineer about this. If you are in New Orleans and live in a pier and beam house, the risk of insulating the subfloor is trapping moisture between the insulation and the wood subfloor, which will lead to rot, mold and infestation. I live in a pier and beam house in So. LA and had to remove hundreds of feet of rolled fibergalass insulation from the subfloor of my house due to this every issue. The previous owners (who had the insullation rolled, had to replace a huge section of the floor because of their error, and it continued to cause problems until I had it taken out.

I understand that there are methods of insullating a subfloor which won't trap the moisture, but you must be careful.


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