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Old 01-24-2012, 12:44 PM   #1
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Insulate below grade family room


The 4' high half-wall in the lower level of my split-level home needs insulating. I'm filling holes in cement foundation wall (from deteriorating form bracket locations where water was coming in during heavy rain). I'm thinking of spray foam, but very expensive. So also thinking of 4mil plastic vapor barrier against wall, then press in fiberglass insulation before replacing sheetrock and paneling. You said not to use green board. I'm next replacing carpet with engineered hardwood on vinyl covered cement floor, using vapor barrier. Will this idea for the walls work? If so, how do I attach the vapor barrier to the cement wall?
Thank you.

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Old 01-24-2012, 12:57 PM   #2
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NO vapor barrier angainst concrete walls.

If at all possible please post some pics.
Is there wood studs there over top a concrete wall?

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Old 01-24-2012, 01:05 PM   #3
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Originally Posted by mae-ling View Post
NO vapor barrier angainst concrete walls.
Why not?

OP, you need to deal with the water infiltration (at the exterior) before you make any headway on finishing the space. The space should be relatively dry even during heavy rains or you will definately have issues with any system you install.
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Old 01-24-2012, 02:55 PM   #4
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Generally, a VB in a basement is not recommended, though recent Canadian studies find that it is often not a problem. Also, cchrc.org just published similar findings in their test trailer, but bear in mind that our winters are cold and dry. Canada is also generally cold, and in those studies I did not see any statements that the VB was essential or even helpful; it rather said they did not appear to affect damage. (I recently posted the references; maybe Gary has them if you can't find the thread.) I still view them as potentially hazardous, and lacking the experience of having looked at 100 houses w/ and w/out, I'd skip the VB and air seal well instead. (Assuming the water intrusion problem was solved, as mentioned above.) Below grade, foam is the insulation of choice, IMO. FB is pretty crappy stuff anywhere. Roxul would be a better batt choice if you want to use batts.
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Old 01-24-2012, 04:06 PM   #5
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Thanks JK for expanding on that subject. There are always alot of factors and arguments that go into that topic and a simple NO can leave alot of people hanging.
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Old 01-24-2012, 05:39 PM   #6
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AG: The name of the Canada study to which I referred is "Understanding Vapour Permeance and Condensation in Wall Assemblies : Volume 1: Main Report", written by the Can Mort and Hous Corp. Pls read it and see if you come to a different conclusion than I did. I did not see any glaring evidence that said "you just gotta have poly in your basement", so I don't understand the rule requiring it. But, then, those guys spell "vapor" in a funny way, too. The cchrc report was focused on adding foam on the exterior for retrofits above grade, but it was interesting that the poly did not seem to be a huge impediment. Many people here use it (including me, back in '80, but not on the new house; MemBrain instead, perhaps) and our city folks mandate it, too (though I am not sure about below grade. I live outside the city and don't GAFRA about their rules, necessarily.) Cheers.
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Old 01-24-2012, 05:43 PM   #7
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Air tightness is far more important than permeability of the assembly in most cases and especially if you keep the surface temp above dew point.

Gotta get rid of the bulk moisture like AG said though.
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Old 01-24-2012, 11:47 PM   #8
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Pls read it and see if you come to a different conclusion than I did.
I've downloaded the *.pdf and will try to get to it soon.
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Old 01-25-2012, 12:44 AM   #9
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AG: "Soon?" I mean, WTF? This is important stink!
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Old 01-25-2012, 09:56 AM   #10
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That article has only reinforced the beliefs I've come to have regarding basements. If you ARE going to place a class I or II vapor retarder within a basement wall system (in a retrofit application only) then it should be placed only at the face of the foundation wall. It was noted in that research that placing fiberous batts only did not have adverse effect as there was enough vapor flow to allow for proper drying. That, of course, only holds true if the exterior drainage is intact and only allows vapor (not bulk water) to enter the system.

Let me first say that the ideal place for the class I vapor retarder is at the exterior face with proper drainage. But, if that is out of the question, I personally believe the "ideal" retro-fit system for basement finishing is this:

From Exterior to Interior:
1) Existing Foundation
2) Drainage Board extended to footing with continuous drain tile placed below floor slab to a sump pit. (http://www.appliedtechnologies.com/f..._400_small.jpg)
3) 2" XPS, tape all seams
4) Stud wall with optional un-faced batt. type insulation
5) Wall finish sheathing
6) Latex paint finish only

The drainage board allows for the inward vapor drive to be diverted down to the drainage system. The 2" XPS acts as a class II vapor retarder and helps to force bulk moisture down. This system will also allow for bulk water leakage while protecting the system from potential bulk-water damage.
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Old 01-25-2012, 01:24 PM   #11
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AG:Sounds good to me. What if you have a PT lumber basement? Still a VB inside the studs? To me, that is where it better be a cold climate.
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Old 01-25-2012, 04:41 PM   #12
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Quote:
Originally Posted by jklingel View Post
AG:Sounds good to me. What if you have a PT lumber basement? Still a VB inside the studs? To me, that is where it better be a cold climate.
Are you talking about where instead of concrete wall you have p.t. lumber wall? I've never really dealt with those walls, so I'd have to research to answer properly. But that could be tricky because air+water+wood=rot where as airtight+water+wood=no rot. So, to keep it wet (poly right against) or not to keep it wet (drain board) is the question...
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Old 01-25-2012, 05:48 PM   #13
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Originally Posted by jklingel View Post
AG:Sounds good to me. What if you have a PT lumber basement? Still a VB inside the studs? To me, that is where it better be a cold climate.
Is there a space between the PT wall or is it tight to the foundation wall?
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Old 01-25-2012, 05:50 PM   #14
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Quote:
Originally Posted by AGWhitehouse View Post
That article has only reinforced the beliefs I've come to have regarding basements. If you ARE going to place a class I or II vapor retarder within a basement wall system (in a retrofit application only) then it should be placed only at the face of the foundation wall. It was noted in that research that placing fiberous batts only did not have adverse effect as there was enough vapor flow to allow for proper drying. That, of course, only holds true if the exterior drainage is intact and only allows vapor (not bulk water) to enter the system.

Let me first say that the ideal place for the class I vapor retarder is at the exterior face with proper drainage. But, if that is out of the question, I personally believe the "ideal" retro-fit system for basement finishing is this:

From Exterior to Interior:
1) Existing Foundation
2) Drainage Board extended to footing with continuous drain tile placed below floor slab to a sump pit. (http://www.appliedtechnologies.com/f..._400_small.jpg)
3) 2" XPS, tape all seams
4) Stud wall with optional un-faced batt. type insulation
5) Wall finish sheathing
6) Latex paint finish only

The drainage board allows for the inward vapor drive to be diverted down to the drainage system. The 2" XPS acts as a class II vapor retarder and helps to force bulk moisture down. This system will also allow for bulk water leakage while protecting the system from potential bulk-water damage.
+1

Good explanation.

I prefer ISO but that is just me. As long as the permeability rating is consistent, that is the key factor. XPS is happier against moisture as compared to ISO but I like the stuff in ISO better.
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Old 01-25-2012, 06:35 PM   #15
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Originally Posted by AGWhitehouse View Post
Are you talking about where instead of concrete wall you have p.t. lumber wall?
Yes. Waterproofing, PT plywood, PT studs, vb, sheetrock. That is what I gathered they were talking about in the Canada "wet wood below grade" references. Maybe I need to re-read that more carefully. Regardless, I'd never use poly inside below grade unless it was a cold-assed environment, and then I think it can be left out if you air seal like a maniac.

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