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Community and Q&A

Cathedral ceiling- vent or no vent

Freddyunfun | Posted in General Questions on

We are having a 4-season addition built (in Wisconsin) and we are planning to insulate the cathedral ceiling ourselves. Builder did not cut in a ridge vent, and used ventilated soffits to match our house. Builder’s practice is to use batt fiberglass insulation to pack all spaces, including the soffits to choke off airflow and create a “hot roof”. Will this work?? Everything I have seen suggests spray foam to seal off the space, or using baffles and cutting a ridge vent to allow air flow. Builder insists their method is good practice. I don’t have expertise other than my research. Any thoughts?

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  1. freyr_design | | #1

    This is not good practice, honestly seems like worse practice than just not venting at all. You should use one of these:

    It is also not to code.

  2. Expert Member
    Akos | | #2

    Ridge vent is easy to add and you end up with a simple vented roof, a robust code compliant assembly. I would not settle for anything else.

  3. Expert Member


    I don't think packing an un-vented roof with permeable insulation meets code anywhere. Your builder should stop doing it for that reason alone.

  4. Expert Member
    BILL WICHERS | | #4

    The batts won't "choke off" the flow of moisture though, and that's ultimately what causes problems in these types of assemblies. You really only have two choices here: 1- put in vent baffles from soffit to ridge in every rafter bay, then insulate however you want under those since you'll have a vented roof, or 2- use closed cell spray foam in every rafter bay with at a layer at least thick enough for your climate zone (probably 50-60% of the total R value depending on where you are), ideally just insulate the entire depth with closed cell spray foam, for a "hot roof".

    What you're builder wants to do is asking for trouble. He may have been lucky with that method before, but you don't want to rely on luck here. As Malcolm mentioned, and I'm pretty sure he's right, your builder's proposed assembly doesn't meet code.


  5. Ryan_SLC | | #5

    My builder did the same thing. No vents, no physical possible way to get R-38 with 1" minimum air...

    So I'm led to believe this is kinda of a tactic by some. "oh! you want it different than how I made it?" Well for a charge, I'll add a roof vent, which is just running a circular saw across the peak. Couldn't be easier.

    The answer is, you are building to code mininum. An unvented cathederal without the intent of spray foam isn't to code. Any where.

    I moved on and didn't follow up with his offer to do insulation which I know would have been how yours describe-ie, wrong by compressing a crap ton of batts in and it would have been completely wrong.

    If you are braver than me, it's their job to build it to code.

    I am still irritated by my experience. If yours is doing the same to you, you'll find you'll be irritated months later that this happened. Framing, sheathing, all has to be to code...but somehow the roof properly constructed for insulation gets a pass? I wouldn't be so nice to mine next time.

    Have your inspector come out and fail it before you have them continue.

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