Q. I’ve heard that if you use 5 1/2-inch-thick fiberglass batts in a 2x4 wall, the insulation will have a higher R-value than standard 3 1/2-inch batts provide. But some people say that compressing fiberglass batts lowers the R-value. What’s the story?

Bruce Harley, an energy efficiency expert at Conservation Services Group, responds: Both statements are correct. When you compress fiberglass insulation, you increase its R-value per inch, up to a point. However, when you compress a batt of a particular thickness, the total R-value does decrease. For example, standard low-density batts, at their...

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