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IECC to Mandate R-60 Roofs

Robert Binder | Posted in Building Code Questions on

It is stated at https://thehtrc.com/2020/insulation-requirements-2021-iecc that the new (2021) IECC code will call for at least R-60 worth of insulation for zone 5 roofs, with comparable changes for other zones and structural elements.

Can anyone in this forum comment on this claim?

Thanks

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Replies

  1. Expert Member
    Zephyr7 | | #1

    I've heard about this too, and it's been being talked about for a while now, but I'll wait to see what actually gets published.

    I think the roof/attic insulation levels are well into the diminishing returns here up over R49. I thought the same when they went from R10 for basement walls in CZ5 to R15. I'm actually pretty sure why that basement change was done, and it's a little on the silly side. Anyway, I'm not opposed to the higher levels in general, I just think they are excessive when mandated as code minimums. Going overboard in the codes drives up building costs, which is an especially big problem for smaller projects with lower income homeowners. There is eventually a point where the energy savings from the extra insulation can't really justify the cost of that additional insulation, and I think we're into that range now. I would rather see tighter air sealing standards instead of higher R value minimums.

    Bill

  2. Randy Williams | | #2

    The 2021 IRC has made changes to attic insulation requirements, zones 4-8 will be required to have R-60. This would be enforced if the 2021 is adopted in your area without being amended. You can view the 2021 energy codes here:
    https://codes.iccsafe.org/content/IRC2021P1/chapter-11-re-energy-efficiency#IRC2021P1_Pt04_Ch11_SecN1101

  3. Jay M | | #3

    Is there any indication on what the uncompressed attic value will be in 2021? From what I understand, if there is an energy heel built into the truss the code only requires requires R-38. With the new 2021 code instead of R-60, should I expect something along the lines of an R-49 "uncompressed" value?

    1. Expert Member
      Michael Maines | | #4

      Jay, if the full depth attic insulation extends across the top plate--i.e., you have a raised heel--you can drop from R-60 to R-49: https://codes.iccsafe.org/content/IRC2021P1/chapter-11-re-energy-efficiency#IRC2021P1_Pt04_Ch11_SecN1102.2.1.

  4. Jon R | | #5

    And R 41.67 on a U-factor basis.

    Apparently R60, with a 118 year payback, is beyond what makes financial sense. Hopefully local authorities will amend back to R49.

    https://www.nahb.org/advocacy/top-priorities/building-codes/code-adoption-kits/2021-international-energy-conservation-code

    1. chicagofarbs | | #6

      I tend to see the NAHB being pretty biased on anything that adds first cost, even if there are benefits to the home owner long term.

      During Illinois state review a few resources said only 15-20 years pay back for R60.

      Easy to skew one way or another based on the model you are using.

      1. Jon R | | #7

        Would be good to see more info from these sources. Evidently the NAHB is not criticizing the vast majority of the code - even where it adds cost.

        1. chicagofarbs | | #9

          Definitely not what I’ve seen in Illinois. There is a proposed amendment by the builders to revert all residential envelope requirements back to 2018 values.

  5. Peter L | | #8

    I'm surprised that Zone 4 is pushing for R-60. Area I am in now only requires R-40 for ceiling. Proper air sealing should be more emphasized than just R-Value in the attic. 30-40% of a homes energy loss is due to air leaks.

    1. Doug McEvers | | #10

      I was thinking along the same lines. An airtight R-30 ceiling may perform as well or better than a leaky R-60. Also, the payback for the attic insulation must take into account the cost of heating fuel for the particular property.

      1. Expert Member
        Malcolm Taylor | | #11

        I'm just guessing, but they probably saw adding more blown insulation to trussed roofs as fairly simple, inexpensive, low-hanging fruit. The alternatives - better windows and walls - both become complicated or pricey quite quickly.

        Our code makes the distinction between the levels of insulation required in attics and cathedral ceilings for much the same reason.

        Not that this possible explanation answers the question as to whether R-60 makes any sense.

    2. Jon R | | #13

      > 30-40% of a homes energy loss is due to air leaks

      This is not true with current code levels of air sealing.

  6. Andrew C | | #12

    If the result of this code, unintended or otherwise, is to get builders to design in energy heels and R-49 to avoid R-60, I'm a fan.

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