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could batt insulation cause probems with condensation

kidbat's Avatar

Join Date: Nov 2001
Posts: 115

02-19-11, 07:09 PM   #1  
could batt insulation cause probems with condensation

I'm finishing a basement laundry room in Wisconsin that has two exterior foundation walls. I've put 1" extruded foam board on the poured foundation walls and built stud walls. My question is weather adding fiberglass batt insulation is more of a pro (for energy efficiency) or more of a con (for prromoting mold growth).

I also have water pipes in half the length of one of the walls. I was going to use foam pipe insulation for noise but also to reduce condensation on the pipes within the wall cavity. I'm not overly concerned about the heat loss as I am about moisture in the wall cavity. Will batt insulation promote mold growth since the insulation may not dry the wall cavity as fast (as compared to having just an open void). I don't have water seepage problems.

Our basement has living space and we control moisture in summer with a dehumidifier. Nevertheless, I'm still concerned that fiberglass batts may discourage air movement (drying) within the wall cavity from condensation on either the pipes or on the styrofoam surface (less likely since humidity should be controlled).

Any insight on whether fiberglass insulation may deter air movement (promoting mold) as a potential problem is appreciated. Thanks!

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airman.1994's Avatar

Join Date: Dec 2005
Posts: 5,579

02-19-11, 08:24 PM   #2  
As long as u don't use a VB u will be fine

drooplug's Avatar

Join Date: Aug 2009
Posts: 4,940

02-20-11, 04:52 AM   #3  
Use unfaced batts.

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GBR in WA's Avatar

Join Date: Mar 2009
Posts: 1,167

02-20-11, 07:55 PM   #4  
Sounds as if you are on the right track! I would increase the foam board on the concrete to R-10 = 2" because 1" may let the water vapor condense on the inside (because the foam is cold due to concrete temp.), wetting the cavity f.g. Your location, with 7-9k HDD is similar to Minnesota, read the sentence just below the chart at 5.1; New Page 1

The cavity insulation should be medium (R-13) or high density (R-15) f.g. to offset the inherent convective loops with that product. Otherwise the heated air will warm the floor framing above effectively. The "biggest Loser" In Fiberglass Insulation.... - DIY Chatroom - DIY Home Improvement Forum

The secret to stopping basement moisture from reaching the cavity is using the airtight drywall approach; Info-401: Air Barriers

Sill sealer under the p.t. bottom plate for a capillary/thermal/air break; Pressure-Treated Sill Plates and the Building Code | GreenBuildingAdvisor.com
No air gap between insulation, no vapor barrier (unless above-grade only if required by B.D.), only latex paint on interior, fire-block the wall every 10' lin. as per Code, block to floor bays above, rigid foam board on rim joist-air seal sides w.canned foam.
Info-511: Basement Insulation — Building Science Information


Info-408: Critical Seal (Spray Foam at Rim Joist) — Building Science Information


kidbat's Avatar

Join Date: Nov 2001
Posts: 115

02-20-11, 10:23 PM   #5  
Thanks for the assurance and good advice. I already have the walls up with 1" foam. I didn't want to spend the extra $$ when I bought foam board, but now I realize I should have just done it right and gone with a thicker foam board.

Thanks for all the info.

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