R38 vs R49/60 attic insulation
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I’m trying to get a sense whether its worth adding more insulation to my attic. Climate zone 5A. Currently has R38 insulation (R11 batt + R27 blown-in fiberglass).
The attic has been air sealed. I could go to either R49 or R60.Â
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Replies
The truth is R 38 is pretty good.
It is very unlikely you could recover the cost of upgrading from R38 unless you live someplace like Alaska using expensive fuel and plan on staying more than 20 more years.
Walta
R49 is still current code in many places, R60 is the newest code required amount for climate zones in the frozen North (including 5A). R38 was code a long time ago, I forget exactly when it changed to R49 in the Northern climate zones.
Anyway, upgrading from R38 to either R49 or R60 is unlikely to pay for itself as walta mentioned, unless you have very expensive heating fuel and do the install DIY (which isn't too hard to do with loose fill (blown) insulation). On new installations, R49 and R60 often make sense, because the material isn't very expensive, so it's not much more money to install the thicker layer during the initial install. For an upgrade like yours though, you're only saving a small amount more in terms of energy, since the R38 layer is already doing most of the "work" of insulating.
Energy Vanguard has a good article about this, with some excellent graphs to illustrate the diminshing returs as you get into higher and higher R values of insulation:
https://www.energyvanguard.com/blog/the-diminishing-returns-of-adding-more-insulation/
Bill