Additional R Value Gained

On a recent job the homeowner asked us what the additional R value was gained by the ceiling insulation we added. Keith says “the dense packed cellulose will be about 3.5 to 3.7 an inch, multiply by 5 inches. This is better than the stated R value of the fiberglass because the fiberglass has a great deal of air leakage and that effectively lowers its R value by half. When insulation companies test the R value in a lab they are doing so in a sealed wall bay. When it gets installed there are gaps everywhere. As air washes over and around the fiberglass it is not a very effective insulator. I see it all the time when I use the infrared camera. You see lower temperatures at all the edges and corners. Cellulose’s greatest value is in its ability to stop air leaks. Many building scientists claim “stopping air leaks” more important than R value. And what else could be done at a low cost and great return on investment? Certainly not tearing down the ceiling and reinsulating with foam board.”

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