How do I calculate the payback period for additional insulation?
Location: Western NC, zone 4, mixed humid
Elevation 2000 ft
Roof: slope 2:12, standing seam.
Attic: formed with trusses and unvented
House roof insulation: Polyiso nailbase R15 min above the deck, netted BIBs below.
This follows on from a question I asked on June 30. We will insulate below the roof deck with BIBs. The cost of adding nailers, netting etc for the insulation is the same if we add the minimum thickness or if we add more. I can add another 1.75″ for $500 to increase the R value from R23 to R30.
I have read some very good articles on this site about calculating the feasibility of additional insulation and I know roof insulation is one of the better places to add more but I don’t know how to get the raw numbers.. We will have a ground source heat pump system. Heating costs will exceed cooling as we get cool night time breezes in summer, we may run a wood fire in winter and on and on.
Is there a simple rule of thumb to apply here to make this simple? Or an online calculator?
Thank you all for your time.
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