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Help insulating a small section of roof

DavidfromPNW | Posted in General Questions on

Hi all. 

This is a second story add using attic trusses. The question is how to insulation the stairwell ceiling coming up from the original main floor to the new second story. As you can see from the pic, this area was site built and required  a full header. Behind the header going down to the original main floor is a cathedral ceiling that was also site built. We obviously when with this cathedral in the foyer bump out to get enough height to get the stairs in. 

Of course the issue is that there is no soffit, and I don’t want to spray foam it. I have read that a good option is to tyvek it and hard pack it with cellulose. it’s a small area and I have removed the planned super slope can lights to eliminate and protrusions into the space. Any thoughts on how to handle this without spray foam?

BTW, I have four super slope can lights for sale if anyone is interested 🙂

edit: slope is 12/12

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  1. GBA Editor
    Martin Holladay | | #1

    First of all, can you tell us your name? (I'm Martin.)

    There is no way to make this a vented assembly. So it has to be an unvented assembly. You therefore have only two choices: either (a) Insulate with rigid foam on the exterior side of the roof sheathing -- I assume it's too late for that (and in any case you only need to insulate a small portion of the entire roof), or (b) Install closed-cell spray foam on the interior side of the roof sheathing.

    If you want to avoid moisture problems, that's what you need to do -- in spite of the fact that you "don’t want to spray foam it."

    More information here: "How to Build an Insulated Cathedral Ceiling."

  2. DavidfromPNW | | #2

    Sorry, my name is David.


    Thanks for the quick response. That's what I was afraid you were going to say. I live in Seattle, so I guess that's a limiting factor. No, there is no way to vent it other than drilling through the headers to create the flow. I guess I can talk to my structural engineer and see what he says.

    So, if I have to go the spray foam route, will a flash and batt be acceptable? It's a pretty small area and I can probably pick up a tank of tiger foam or some other brand (any insight on the least offensive of the group would be great) and flash it with 2" and batt it with the rest. Guessing that should resolve the dew point issues. As I mentioned, there are no penetrations so air leakage from inside to out will be virtually non existent.

    1. GBA Editor
      Martin Holladay | | #3

      Q. "Will flash and batt be acceptable?"

      A. Yes. For more information, see "Flash-and-Batt Insulation."

  3. DavidfromPNW | | #4


    Thanks again. I guess I'll have to do the flash and batt in that section. I believe Seattle King County is climate zone 4c so my 2" guesstimate is spot on. Very likely that I will not find a contractor to flash this very small area (70-80 square feet), so I'll have to go the DIY route.

    I've used Tiger Foam in a addition I did once before and was happy with it. That said, do you have any recommendations for what's best out there. My preference would be something that is effective and less toxic from an off gas perspective, or is that just another unicorn?

    Thank you,


  4. Expert Member
    Peter Yost | | #5

    Hi David -

    you ask a good question: who has the lowest environmental 2-part spray foam "froth pak?" The new blowing agent with a global warming potential of just 1 uses a hydrofluoro-olefin, or HFO.

    I just did a bit of searching and could not find any "small batch" package two-part foam kits using the new HFO but I am researching; stay tuned.


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