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2018 IRC to allow air-permeable insulation in unvented attics in hot humid climates when combined with with a vapor-permeable air barrier at the ridge

David ButlerDavid Butler Posts: 3,889
Here's an article from Builder Magazine that explains the recently approved code change: http://bit.ly/2cUMtbH

And here's a background article by Joe Lstiburek: http://bit.ly/2ciNbuV

If someone has a link to the approved language, please post.


  • Looks like this is specific to climate zones 1,2 & 3.
  • Thanks for calling that out, John. I meant to include that detail in my post. According to Joe, this could be extended to colder zones, perhaps in the next code cycle:

    "Does this work everywhere? Sure about DOE/IECC Climate Zones 1, 2 and 3. Pretty sure about Climate Zone 4, but need more work to be sure. Climate Zone 5 and 6 need a lot more work. Lots of weatherization dense pack cellulose experience to draw on. But need to be cautious here. Confident we can make it work but the details need to be worked out. Need a year or two more."
  • We finally have WX contractors sealing the floor and walls of crawl spaces instead of hanging permeable insulation from the ceiling. Now there's an option to revert to the same old method in attics? Sorry, but the better solution is spray or rigid foam on the underside of the roof for an unvented attic, in ANY climate zone. Otherwise, I think we're inviting trouble, like the old crawlspaces and poorly-vented attics.
  • David ButlerDavid Butler Posts: 3,889
    Just as an update, this change was approved by consensus vote in December. Attached is the proposed language as approved.