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Old 12-31-2010, 09:51 AM   #1
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Basement Insulation Help?


Hey gang. I'm building a rec room in my basement and hoping you can get me in the right direction. Right now my head is just spinning about this.

I live in a house that is 5 years old and owned since new. Basement is dry and sump pump runs very little. The climate changes greatly through the year. Poured concrete foundation about 8' high. The upper 2'-3' is above ground. The builder ran a pink fiberglass blanket insulation covering the upper 4' of the wall.

Because the comfort level has been acceptable and no moisture issues, I was going to simply frame and drywall and not do any more insulating.

A guy that I know in the construction biz told me that I would be stupid not to add more insulation. He said that I should insulate my stud walls and cut the vap bar in the back (covering the blanket) because you want your vap bar on the warm side and not 2 vap bar's

Keep in mind that my concern is not comfort but not creating an enviroment for condensation/mould. This is where my head starts spinning.
I feel that cutting that vap bar in the back is going to open up a whole can of worms. I would need to make sure that there is zero warm air getting in behind the walls, and there are lots of spots where this will be hard to do- (around bulkheads, where ceiling joist pockets meet the exterior wall, and at the ends of my walls where the framing/finishing will not be done at this time).

I forgot to mention that the framing is done so spray foam and foam board is out.

I'm wondering if I should go back to plan A and not do any more insulating. There are only 2 concerns that I can think of with this. First now that I have built walls and cut down on the air movement, will that create a condensation problem? There will still be some movement around the exterior perimiter and up into the joist pockets. Second if I'm creating a consistantly cool space behind my framed walls will I get condensation behind my drywall?

If you have made it to the end of this post, I thank you and appreciate any advice on this. I just want to make sure it's done right

Jim

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Old 12-31-2010, 10:08 PM   #2
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Basement Insulation Help?


2 comments. (1) slitting a vapor barrier, which you likely do NOT want against concrete, does virtually nothing. (2) I'd suggest you do some studying on buildingscience.com, and search here. This has been talked about many times. Good luck w/ the job. j

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Old 01-02-2011, 02:20 PM   #3
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Basement Insulation Help?


This is exactly the issue I need to have explained, so hopefully someone in the know will lets us know what we have to do. My preference will be to extend the existing form of insulation down to the floor level and then enclose all with 2X4 framing in which I plan to run wiring, plumbing and ducting for the heating so it comes out at floor level rather than from the ceiling.

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Old 01-02-2011, 02:41 PM   #4
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Basement Insulation Help?


2" xps with construction adhesive to concrete
Frame
3" loose batt (no paper) insulation between studs
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Old 01-02-2011, 03:35 PM   #5
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Quote:
Originally Posted by Jackofall1 View Post
2" xps with construction adhesive to concrete
Frame
3" loose batt (no paper) insulation between studs
The XPS would be applied to the exposed concrete which will continue to allow it to breath and then the 2x4 studs place in front of everything else being kept .05 inches off the floor. Wiring, plumbing and ducting can then be installed afterwhich the 3" loose batting (no paper) is installed before appliing the drywall or other wall covering?
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Old 01-02-2011, 03:57 PM   #6
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Basement Insulation Help?


Use a pressure treated 2x4 on the floor, trying to leave and air gap on the floor is near impossible. The XPS will be the vapor barrier and is moisture resistant.

As for the OP having already studded walls, I would try and slip 6 mls plastic behind the studs and then insulate with 3" loose vat insulation and yes it is worth insulating all the way to the floor.
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Old 01-02-2011, 04:15 PM   #7
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Will the XPS allow the lower portion of the concrete to breath? I'm being told by Buildingscience.com to use EPS as it is semi-permeable to water vapor and thus will continue to allow the lower portion of the concrete wall to dry inwards which it is doing now by design. I just have to provide thermal protection using drywall? That's why I had a question mark behind my previous statement as I was looking for your confirmation.
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Old 01-02-2011, 04:36 PM   #8
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EPS - Expanded Polystyrene Foam
XPS - Extruded Polystyrene Foam

The differences between the 2 are R value/inch (XPS 4.5-5 EPS 2-3) and cost and rigidity, both are recommended for foundation insulation.
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Old 01-02-2011, 04:47 PM   #9
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Are both semi-permeable?
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Old 01-02-2011, 06:13 PM   #10
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Quote:
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Are both semi-permeable?
XPS - perms .4 - 1.2 per inch of thickness
EPS - perms 2.0 - 5.8 per inch of thickness

They are both permiable, EPS is more permiable, but loses R-value with increased moisture content.

Personally I would go with XPS, but thats just my chosen direction, if asked what I would recommend, it would be the same as what I would use XPS.
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Old 01-03-2011, 09:30 AM   #11
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Here in the NE it is recomended to cover you foundation walls with rigid insulation with a perm of 1.0 or greater. This will allow the concrete to breath and keep warm moist air from condensing on the concrete wall (all seams must be taped and sealed). From there frame you 2x4 walls using PT bottom plate and insulate with batts. DO NOT use plastic sheating against your concrete this will only create moisture issues later.

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