I love insulation. It’s a wonderful thing because it saves energy. It makes buildings more comfortable. And it’s pretty inexpensive considering how long it lasts (or should last). I get asked a lot for my opinion on the best insulation to put in a building and my answer is straightforward: A well-installed insulation is the best. I like fiberglass. I like cellulose. I like spray foam. I like mineral wool. I like blown, sprayed, batt, and rigid insulation.
Yeah, different materials have different properties, with their advantages and disadvantages. But if it’s installed well and protected by good water and vapor control layers, it should do its job for a long, long time.
So, what are my two ways to make sure you get the most out of your insulation? Both have to do with installation.
1. Request a minimum thickness
Way back in 2011 I wrote an article called “Is There a Downside to Lumpy Attic Insulation?” I refer to it now and then but it’s important enough to make it the highlight of this article. The point of the article was that if you install insulation uniformly, as in the lead photo above, you’ll get much better performance than from insulation installed (or later disturbed) like you see in the photo reproduced as Image #2 at the bottom of the page. Flat beats lumpy.
In that article, I showed an example of an attic done two different ways. First, you insulate the attic uniformly to a thickness that gives you R-30 everywhere. You can’t do this in a typical attic because the roof framing doesn’t give you enough space over the eave walls to get full thickness so you’d have to do something like use raised-heel trusses. But we’re going to assume here that…