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Community and Q&A

Is it worth it to add more attic insulation on top of R-40?

Joe Blanco | Posted in General Questions on

My house was built in 1989, the attic originally had fiberglass batts with loose fill rock wool. A couple of years ago cellulose was added to bring the overall R value to about 40 (hard to calculate exactly because the weight of cellulose also compressed whatever that’s beneath it). Now with $300 I can add 4 more inches of cellulose to bring it to about R50. Is it worth the cost?

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  1. Joe Blanco | | #1

    I forgot to mention that I am in zone 5, but also one mile away from the border of zone 6.

  2. GBA Editor
    Martin Holladay | | #2

    If I were you, I would probably make the investment in the extra insulation. But if you want a technically accurate answer, I would have to say, "You haven't provided us enough information to answer."

    To know the payback period for the added insulation, we would need to know all about the characteristics of your home's thermal envelope (so that we knew what percentage of your home's annual heat loss is attributable to your attic), and we would need to know more about your heating system, your heating fuel, and your heating fuel cost.

    Other important factors include your predictions about future energy costs and the length of time you intend to live in the house before selling it or moving away.

    For more information on this issue, see Payback Calculations for Energy-Efficiency Improvements.

  3. Joe Blanco | | #3

    Yeah I sense it's going to be more complicated. I am currently using a mod-con boiler (about 90% efficiency) with propane, the fuel cost is $2 per gallon (it's been the same price in the last four years). House is 25' by 50', so the ceiling area is roughly 1250 sq ft.

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