I was walking the insulation aisle of a big home store today when to my dismay I saw wrapped fiberglass insulation is back. This is batt fiberglass insulation that is in a thin perforated plastic sheathing so that the fiberglass is contained in a tube of sorts. It’s supposed to be easier to handle. I’m not so sure about that, but I am sure that this type of insulation is usually bad news.

When I first saw this kind of insulation about seven years back, its maker made the claim that the insulation was safe to install over existing insulation (even though it’s wrapped in plastic, or, one could say, “faced”). They said because of the perforations in the plastic wrapping, it would still allow water vapor to pass through it. It doesn’t. The company (hint: they make pink insulation) isn’t making that claim now – or at least I didn’t see it on the label – but buyer beware! Don’t put this insulation over existing insulation and assume that it will breath. It absolutely simply doesn’t. I know, because I didn’t believe it then. I bought a roll, tore off some of the plastic wrapping (holes and all) and then using the perforated wrap I covered a steaming pot of water. Sure, some of the water vapor probably did escape through the holes, but a lot of it condensed on the underside of the wrapping. (Experiment with this yourself: take some kitchen plastic wrap and punch holes in it, then cover a glass that you just filled half way with steaming water, and watch what happens.) If you use this wrapped insulation, you invite the same potential condensation in your attic.

And what is “nice” about it, anyway? You really shouldn’t install it without a mask, eye protection, gloves, long sleeve shirt and pants, etc. anyway. At least I wouldn’t. (Once you cut the roll, you’ve exposed the fiberglass, and it’s no longer so “nice”.) Buy the regular unfaced batts instead. They’ll let water vapor through and, besides, they’re cheaper.

To me, this stuff is such a rip-off. I have had clients remove this type of insulation when I’ve found it in their attics over the top of older insulation. The most recent one was a widow, and she didn’t need this kind of headache. For all I know, perhaps her late husband installed it, thinking he was taking good care of their house. So, in addition to paying for the materials and the time (or expense) to have it installed, sorry to say but it now really needs to come out. (Fortunately, one of my recommended insulation contractors was willing to unwrap it for her and re-install the old fiberglass.)

Simply put, it’s not good for the durability of the home: it will allow water vapor to condense, and any water in a home where you don’t want or expect it can be a nasty thing. Think mold or rot. Besides, there are so many other good alternatives (unfaced batts, blown fiberglass, blown cellulose).

This entry was posted on Tuesday, March 16th, 2010 at 8:40 pm and is filed under Building Science, DIY, For Homeowners, Professional Tips. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.