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Old 06-07-2009, 11:36 PM   #1
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best way to put insulation under a house


I have a 12 by 16 room that is up off the ground I want to put r13 under it I was going to put it up and then put some osb up so that the dog and cats can not get in to it I know that the osb is more than I need but the price is good on it and the room is small so I was thinking I will get some more r out of the osb but others have been telling me that I will get mold if I use osb to cover it up and are tell me to put wire up the insulation has a vapor block on both side it is like it is in a plastic bag but it has small pin hole in it I have the osb and can take it back can some one pleas tell me the best was to do this I live in Louisiana thanks

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Old 06-08-2009, 06:07 AM   #2
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best way to put insulation under a house


Not sure what is correct down south. Up here in this climate, I would use rigid foamboard insulation since, it open to the weather. Might cause moisture problems down south. Check local codes or practices. They do make insulation already in plastic bags. But I would add more that R13, if possible.

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Old 06-08-2009, 08:06 AM   #3
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best way to put insulation under a house


what about spray foam.where i live you can rent the equipment
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Old 06-08-2009, 09:38 AM   #4
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best way to put insulation under a house


Due to the humidity levels under the house I would paint the osb with a good exterior paint.
I would also ask, are you sure the R13 is enough?
Ron
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Old 06-09-2009, 01:08 AM   #5
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Originally Posted by Ron6519 View Post
Due to the humidity levels under the house I would paint the osb with a good exterior paint.
I would also ask, are you sure the R13 is enough?
Ron
R13 is what is call for here in wall and floor not real cold here for long time in winter just short freeze time one or two time a year and back up in the 50 by noon Thank you for telling me about the exterior paint.
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Old 06-09-2009, 01:12 AM   #6
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what about spray foam.where i live you can rent the equipment
we do not have that here I went to Lowe's and asked and look all we have is the foam in a small spray can and it would cost to much to use but thank you for getting back to me
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Old 06-09-2009, 08:28 AM   #7
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best way to put insulation under a house


Do you use AC in this room?
If so more insulation would help on that cost
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Old 06-09-2009, 08:43 AM   #8
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best way to put insulation under a house


Hey, grillman, sounds like you're in south La. Common practice over here in homes on pier and beam foundations is just kraft faced fiberglass, with the facing up against the floor and installed with wire supports. I like the perf encapsulated better, though. I wouldn't put the osb under it. You'd not only have the possibility of mold, but it would create the kind of space that roaches like to breed in if it does trap any moisture. That said, it might last a long time without any problems, but if they do occur it's a real pain in the butt. Not worth taking the chance to me.
As far as the animals go, dogs and cats usually won't bother it, though I've known a few dogs that would chew on just about anything I'm more concerned about raccoons and possums under the house. Best thing is to skirt the house with lattice, either treated wood or pvc, to keep them out and still let it breathe. Looks better, too. You should also put down a 6 mil plastic sheet on the ground under there if you don't already have it.
The only thing I've ever seen messing with the exposed fiberglass is mockingbirds stealing little bits of it when they're building nests, but they usually won't go through the lattice to get it.

Last edited by ratherbefishin'; 06-09-2009 at 09:08 AM.
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Old 06-09-2009, 09:03 AM   #9
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Do you use AC in this room?
If so more insulation would help on that cost
Good point, Dave. More is always better, IMO. I prefer to use R19. Down here, though, if it's just a crawl space where the wind doesn't really blow through it R13 is adequate. IIRC, DOE recommendation for floors here is only R11, but I always take those to be absolute minimum. Close to water, where the piers are 8' or taller, R19 is the standard and those can be safely enclosed without moisture problems....at least until the surge comes
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Old 06-09-2009, 09:34 AM   #10
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If it's well ventilated underneath then I don't see the harm in adding the osb. It wouldn't be any more prone to condensation than the walls are covered with siding. Key words are well ventilated.
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Old 06-09-2009, 10:04 AM   #11
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Key words are well ventilated.
Yup, and a good ground barrier. If it's on high ground with good drainage can make a difference, too. From what I've seen in the few years I've been down here, though, I won't enclose it unless it's at least 4' off the ground. But that's just me....I hate mold and roaches....thinkin' seriously of moving back to a drier climate in a couple years
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Old 06-09-2009, 11:02 AM   #12
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best way to put insulation under a house


roxal insulation is not bothered by water and if you wanted to put the osb under there what about taking a piece os peg board(the one with all the holes in it) and ripping it down to 1 foot by 8 foot strips and putting 2 rows of it in there for ventalation.you could paint everything with thompson water sealer before putting it up (both sides)
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Old 06-09-2009, 03:21 PM   #13
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best way to put insulation under a house


Let's not get too crazy about the more insulation the better. Everytime you double insulation you reduce your heat loss by half. That means:

R1 saves 50% heat, and loses 50%
R2 saves 75% heat, and loses 25%
R4 saves 87.5% heat, and loses 12.5%
R8 saves 93.8% heat, and loses 6.3%
R16 saves 96.9% heat, and loses 3.1%
R32 saves 98.4% heat, and loses 1.6%
R64 saves 99.2% heat, and loses 0.8%
R128 saves 99.6% heat, and loses 0.4%

At R13 he saves 96.15% of the heat/cold and loses 3.85%. If he moves up to R26 instead he's going to reduce his heating/cooling through the floor by just 1.92%/year and still lose the same through the walls & attic. So, insulating the floor to R26 vs. R13 probably won't even save 1% to his total heating/cooling bill. It may be worth it to insulate it higher than R13 if it's real easy and cheap to increase the insulation, to be green , or the owner expects to live many years in the same place.

In high moisture areas as mentioned I'd paint the OSB and use XPS foam which is impervious to moisture and the right tool for the job in water/moist/ground/basement type situations. Just make sure none of the XPS is exposed to sunlight, sunlight slowly turns it to dust.

Last edited by Piedmont; 06-09-2009 at 03:38 PM.
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Old 06-09-2009, 03:24 PM   #14
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Originally Posted by Piedmont View Post
Let's not get too crazy about the more insulation the better, especially dealing with foam. Everytime you double insulation you reduce your heat loss by half. That means:

R1 saves 50% heat, and loses 50%
R2 saves 75% heat, and loses 25%
R4 saves 87.5% heat, and loses 12.5%
R8 saves 93.8% heat, and loses 6.3%
R16 saves 96.9% heat, and loses 3.1%
R32 saves 98.4% heat, and loses 1.6%
R64 saves 99.2% heat, and loses 0.8%

At R13 he saves 96.15% of the heat/cold and loses 3.85%. If he moves up to R26 instead he's going to reduce his heating/cooling through the floor by just 1.92%/year and still lose the same through the walls & attic. So, insulating the floor to R26 vs. R13 probably won't even save 1% to his total heating/cooling bill.

In high moisture areas I'd paint the OSB as mentioned and use XPS foam (just make sure none of the foam is exposed to direct sunlight, the sunlight will turn it into dust).
Do you have a link to where these numbers come from?
Thanks
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Old 06-09-2009, 10:18 PM   #15
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best way to put insulation under a house


I'd still use something thicker than r13. I feel like that's a wasted effort. Spend an extra few dollars and put something in worth using. I may be off base since heat loss is more of a concern here but I believe code is r30 under the floor. I don't think you could even get away with r13 in a 2x4 wall here

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