A.Energy and sustainable design consultant Andy Shapiro responds: Every inch of insulation you add to an attic results in less savings than the previous inch you added. That’s just the way the physics works out. The good news is that adding another inch of insulation in an attic costs very little, if any, in added labor, so it’s mostly added material costs. For a house in central New York (6,700 degree days) with typical efficiency oil heat (75%) and oil at $1.25/gallon, the cost for the heat lost through the insulation in a 1,200-sq.-ft. attic for a typical year is summarized in the table below.

Local codes usually dictate the minimum acceptable level of attic insulation. What kind of savings can a homeowner expect when they upgrade from R-30 to R-40? It would be worth another $20 in the first year. If the homeowner expects a simple 10-year payback, then up to $200 could be spent on the upgrade to R-40, and still be worth it. The added...

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