Are You Confusing Insulation with Air Barriers?
I read a lot of stuff online about insulation and air barriers and other building science topics. I see a fair number of articles bashing certain products or materials. Sometimes it's because the author sells a competing product. Sometimes they just don't like a product. Take fiberglass insulation, for example. What thoughts just went through your head?
Those who have some building science training will look at the photo above and immediately see the symptom of a problem. The places where that formerly yellow fiberglass insulation has turned dark grey are places where air is moving through the fiberglass.
Some people will jump from that symptom straight to a guilty verdict for fiberglass. Sometimes they'll even derisively call it "filterglass" because it doesn't stop the air from moving through it.
But is the type of insulation really the source of the problem here?
What about the photo below? It's another case where the light-colored insulation has turned dark by picking up dirt from the air moving through it. Is the problem that they used an air permeable insulation material?
Or could it be that there's a huge freakin' hole in the ceiling!? Seal the hole and the fiberglass will perform a lot better. When you think in terms of building enclosure control layers, it's a lot easier to assign the blame correctly.
A good building will have control layers that control the flows of heat, air, and moisture. Just because a failure in the air control layer (air barrier) shows up in the heat control layer (insulation) doesn't mean it's the fault of the insulation.
Hey, I've bashed fiberglass here in this blog. I wasn't condemning it as a product, though; the way it often gets installed is what irked me. (I heard from one of the manufacturers about that article, but that's a whole other story.)
But fiberglass and other air-permeable insulation can work just fine. It can be installed well, too. Here's a perfect example of a Grade 1 installation I saw in Nashville a few years ago.
Everyone has their preferences, and that's fine. But if you're going to argue against a product, make sure you're using valid arguments. Dirt showing in fiberglass insulation isn't a valid reason to convict fiberglass.
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