Fiberglass insulation between furring over XPS?
Gregory Worrel| Posted inEnergy Efficiency and Durabilityon
I have insulated my basement walls here in Detroit with 2″ XPS. We have fastened 1×3 furring strips over the XPS using Tapcon screws. I am wondering if there would be any problem with compressing 3.5″ unfaced fiberglass batts in the space between the furring strips. 1/2″ drywall will go over the furring strips.
I am putting a home theater in part of the basement and I think that filling the empty space behind the drywall might be a good thing acoustically. The extra insulation value (small I am sure due to the compression) would just be a bonus. I just want to make sure I won’t be creating some other problem. Thanks.
Greg
Replies
Gregory,
Every basement is different. Some are quite dry; others are occasionally damp.
My own advice is consistent: NEVER install fiberglass in a below-grade wall. If your basement is a little damp, the fiberglass gets soggy and moldy.
That said, installing the XPS goes a long way toward limiting your risk, because you no longer have a cold condensing surface (the cold concrete). Some building scientists (including Joe Lstiburek) give the thumbs up to details like the one you are proposing.
Call me conservative, but I don't like fiberglass batts in basements. The final choice is yours, of course.
Gregory,
I do not see a problem with your idea. Just make sure you caulk/spray foam the XPS (at the base, top, and around windows) and tape all the seams.
Thanks for the replies. Martin, I understand your advice and I have had high humidity in the basement before I put the XPS up. In most past years I have run a dehumidifier in the basement in the summer months, but for comfort more than any distinct problem. I did not use a dehumidifier last year (all but 20% covered with XPS) and didn't notice a humidity problem.
I wanted to use paper-free drywall but could not find it so we are using green board. We are keeping it a couple of inches off the floor. I had a water heater failure that put an inch in the basement and have had sewer backups once or twice in twenty years but never more than an inch or so.
We have used spray foam as the glue and to seal the XPS on all edges and also put 2" XPS in the joist cavities sealed with foam. We have taped all the seams.
A popular acoustic tip for a home theater right now includes putting 1" thick compressed fiberglass (Linacoustic duct liner) below ear level over the top of the drywall as an absorber on 3 walls and full coverage on the front wall with acoustically transparent fabric over it for aesthetics. Many people use double drywall for its soundproofing value. I will probably double the drywall on the interior wall but it seems unnecessary on the outside wall. I plan to stuff fiberglass or rockwool insulation between the ceiling joists for bass absorbtion and soundproofing.
At this point I plan to leave the drywall on the outside wall unsealed at top and bottom so there should be no problem with moisture being trapped behind it.
Thanks for your help.