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R19 and vapor barrier questions


montyface's Avatar
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Join Date: Sep 2005
Posts: 49
MA

12-13-09, 05:23 AM   #1  
R19 and vapor barrier questions

I'm in the process of finishing my basement. A few questions: Should I use greater than r19 for outside walls? I currently have r19 without paper backing on outside walls. Should I install new insulation with the paper vapor barrier or use plastic over what I currently have? For an inside wall to an under stairs storage space, should I have the paper vapor barrier facing the drywall? Thanks

 
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Bud9051's Avatar
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ME

12-13-09, 06:04 AM   #2  
Not sure how you progressed to where you are, so can't be sure new advice is correct. We need to know approximately where you are. Your profile is a bit vague (USA). What is up there with the r-19, assumed to be fiberglass? Is it against the foundation wall or is there an air gap? How much of the walls are above grade? All basements have moisture issues, how do you intend to dissipate that moisture?

That will get us started.
Bud

 
montyface's Avatar
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12-13-09, 07:08 AM   #3  
Sorry. Home is in Massachusetts. All insulation is fiberglass. Basement is ground level. Insulation is in studded bays. Kneewall foundation is not yet insulated...needs to be studded out. At the moment, the intent is to drywall the studded walls above the foundation.

 
Bud9051's Avatar
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12-13-09, 07:38 AM   #4  
Hi monty, cold country so not a lot of ac. Moisture migrated through concrete with almost no exceptions. If it is blocked by a vapor barrier, it can accumulate, so below grade, no vb on either side of the fiberglass. The fg should not be in contact with the concrete.

As for the amount of insulation, above grade is the primary concern, including the rim joist. Use some caulking or can foam to seal that rim well at all seams and where it rests on the foundation. Below one foot below grade, the resistance of the soil starts to add to your r-value. The heat migrates into the soil, but has some distance to travel before it gets blown away, thus below grade the r-19 if more than enough. Some elect to add NO insulation below that one foot line to allow some heat to hold the frost at bay.

For the "inside wall to an under stairs storage space" you have moisture from the concrete and cold temperatures. Those conditions, if isolated, will lead to a damp musty storage area. I would omit the insulation and glue some rigid insulation directly to the concrete. Also seal the rim joist in that area if exposed. If the space is isolated from the heat and exposed to the outside, it will go to the outside temp, burrrr.

Here is some reading: BSI-009: New Light In Crawlspaces —
BSD-103: Understanding Basements —

8 degrees here this morning, hope you are a bit warmer

Bud

 
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