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Insulation for basement


dcs6f4's Avatar
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04-25-15, 03:21 PM   #1  
Insulation for basement

I have a poured concrete foundation---house was built in 1996. All the wood in contact with concrete is pressure treated and I have passed the rough-in inspection. The concrete wall is bare at this point (no vapor barrier, dry-lock etc.). My initial plan for insulation was kraft-faced fiberglass insulation in the stud bays (with the ~1 inch space between the studs and concrete foundation) so no insulation will touch the concrete and using a dehumidifier to control humidity in the space.

I am the second owner of this home and in 3 years I have never had any problems with water in the basement, condensation on the walls, etc. The previous owner (who was the original home owner) said the same. Still with all the information out there I want to do what I can to avoid mold in the future.

I have heard that the kraft paper is probably going to cause more harm than good in my situation due to its ability to trap moisture between the walls and fiberglass. I am contemplating using the kraft paper to staple each piece of the insulation to the studs and then cutting off the rest of the paper to allow for dissipation of any moisture (this way it will stay in place for sure). I have also considered placing holes in the drywall every so often with a return air grate attached to allow for better air circulation and control of moisture behind the walls with the dehumidifier.

I acknowledged the fact that I should have thought this through before framing and that there are many better options, but just trying to work with what I've got.

 
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Keith Weagle's Avatar
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04-25-15, 03:56 PM   #2  
Just so it is clear, have you already framed up your stud wall?

 
dcs6f4's Avatar
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04-25-15, 04:02 PM   #3  
Affirmative... Posts have to be at least 25 characters hence this sentence.

 
Keith Weagle's Avatar
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04-25-15, 04:13 PM   #4  
Your vapour barrier should have been on the concrete wall from grade level to floor before the wall was framed. Since that cannot be done now, my first suggestion is to have someone come in and spray foam. That will solve a few problems. next best option would probably be to use 1" foam between the studs with spray foam behind the stud and concrete. The goal is to create a vapor barrier with the wall already in place, but on the concrete side. If you can achieve that you can go on to finish insulating the wall with batt insulation. It depends how the outside wall has been treated as to weather or not you install a vapor barrier on the inside under the drywall.

 
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04-25-15, 04:32 PM   #5  
Hi dcs,
here is some reading for you:
Joe Lstiburek Discusses Basement Insulation and Vapor Retarders | GreenBuildingAdvisor.com

Bud

 
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04-25-15, 05:03 PM   #6  
Thanks for the replies and the resource. I do realize that spray foam is ideal and will certainly get a quote or two.

One question I have is whether unfaced fiberglass is really that bad in basements. It seems to me I'd be hearing about an epidemic of mold problems if it were. I don't mean to discount any advice, just interested to know if mold is pretty much a certainty with the plan I indicated in my original post.

 
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04-25-15, 07:04 PM   #7  
How much certainty would you consider acceptable?
The problem with mold is once you have it you can't erase that fact. The least expensive way to eliminate mold is to never let it get started.
As for fiberglass, it would be my dead last choice because it allows air to circulate through it, warm humid inside air can reach the cool foundation wall and produce condensation.
Basements face outside water, moisture vapor from the soil, moisture vapor from below the footings, inside humidity, and broken water pipes. Resources on moisture issues in basements are almost endless and before you finish reading them they will probably change their minds. Insulation levels have changed and now they are saying a vapor barrier is ok, as long as you don't trap anything that will feed the mold between the vb and the concrete.

I'll add one more link, but search their web site and you will find more articles.
BSD-103: Understanding Basements — Building Science Information

Bud

 
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