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I am working on installing insulation in our home. We bought way too much insulation, and i was wondering what the effiency of doubling up and throwing an extra layer on top? We are using R-38 12" thick batts. Basically is it worth the money to add another layer if we live in a very cold environment, shady side of hill, and have a huge attic space that is at this time fully covered with 1 layer?

  • What does "very cold" mean? Opinions on that vary widely. – isherwood Sep 26 '17 at 15:01
  • I'd also be curious how you installed 12" batts. Are they between joists? Are there voids above the joists? – isherwood Sep 26 '17 at 15:17
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Short answer: Yes

Install as much insulation as you can afford. It will pay for itself in the long run. If you have space in the attic, then another layer would certainly help.

Make sure you don't restrict the ventilation of the attic by blocking eave vents.

Good luck!

  • If "very cold" means low 40s, payoff for R-76 is geologically long. – isherwood Sep 26 '17 at 15:01
  • Yes, there are a lot of calculations that would be relative to the instant case but generally more insulation is better. The payoff may come when you show your heating bill to the next buyer. – ArchonOSX Sep 26 '17 at 15:50
  • Not to belabor the point, but adding R-38 on top of R-38 only has significant benefit if the walls and windows are adequately insulated, and if the climate is truly cold. In cold-ish climates and with homes built before the 1970s this may not be the case, and it's just a waste. Also, if the OP didn't install the first layer properly (say leaving an air gap below), the second layer is completely pointless. – isherwood Sep 26 '17 at 15:54
  • Well i live in spokane, we've seen weather yere in the -20, -30, and it is expected that it will remain between 0 and -10 for a week at the least. Could be worse though. – Bobby Sep 26 '17 at 18:00

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