When I was asked to help teach a class on how to choose insulation, I knew that it would have to include examples of different ways to insulate slabs, basements, and crawlspaces; walls, ceilings, and roofs; and tricky areas like rim joists and kneewalls. I also hoped I could offer a systematic approach to evaluating products, so that the folks that participated in the class could learn to determine for themselves if a material was right for their projects. To do this, I started to develop a list of criteria to consider when choosing insulation. When I thought I was done, I ran it by a few colleagues and asked a few designers and builders a number of specific questions about how they settle on insulation in their work. I ended up with seven (+) points that need to be considered when choosing insulation. Then I started to rethink my approach altogether, but we’ll get to that a little bit later. First, let’s take a look at the list I came up with.
How well insulation slows heat transfer is quantified as R-value. The higher the number the better when it comes to R-value. When you see R-values listed, it’s important to know if they are the total R-value for a product or an R-value for the material, which is usually given as R per inch. For example, you can buy an R-13 fiberglass batt designed to be installed in a 2×4 wall. That’s the total insulating value for each batt. If you are blowing loosefill fiberglass insulation into an attic however, the product is likely sold at around R-3 per inch. The total R-value will depend on how deep you blow the insulation (as well as it’s density).
Because standardized R-value testing measures all three…
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