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Can you mix and match vented and unvented roofs?

jmfb_k7 | Posted in General Questions on

I am looking to build using a hip roof for the majority of the house (its a 50′ square in essence), but in the rear corner is a great room with a vaulted ceiling (to be cliche I guess) so it will be gabled. Where the vault meets the hip will be a valley and I think it will be next to impossible to vent. So I would like to have it designed unvented (maybe with 5″ exterior foam, dense packed joists). But the rest of the roof could likely be vented well (or as ok as a hip can be vented).

Can these two intersect ok? Should I run the exterior foam underneath the valley and down to the ceiling plane (since the attic temp will likely be close to exterior temp in the winter) to keep the vaulted sheathing warm? I was wondering if they could frame and insulate the cathedral before framing up the rest of the roof to make it easier (or would this be harder)?

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  1. user-2310254 | | #1


    I'll give your post a bump. It would be helpful to know your climate zone or ZIP.

    1. jmfb_k7 | | #2

      Thanks Steve, this would be for climate zone 6, but right on the border of climate zone 5 (IL/WI border between Milwaukee and Chicago).

  2. Expert Member
    Akos | | #3

    Combining the two is possible but air barrier continuity is problematic. I was faced with a similar dilemma and end up changing most of the roof to unvented so I wouldn't have to deal with it.

    There are many ways of building cathedral ceilings that can be vented. I would go with a truss design that allows for enough space for venting and insulate the same as the rest of the house. If the ceiling in the cathdral section is low slope (I think less than 4 in 12), loose fill will settle for simple insulation.

    If you want steeper ceiling you can still loose fill if you have a mini attic built near the ridge that can contain extra insulation. This extra insulation near the top helps top up any settling lower down.

    Make sure to figure out your vent baffle installation as this is always needed to contain the insulation and keep a vent channel open.

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