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Continuous Insulation Detail

RidgeHouse1950 | Posted in General Questions on

Do I have this exterior insulation detail of the roof to wall transition detail drawn correctly?
This is new construction in Zone 5 near Lincoln, Ne.  I am planning on applying Henry VP 100 outboard of the sheathing.  The Henry rep indicated I should use Henry’s RF 200 roof and ice dam on the roof sheathing, but I’m not sure he understood the term exterior insulation.  Is it correct to use the RF 200 or the VP 100 on the roof sheathing under the insulation?
I think I’ll apply 2 layers of 2″ polyiso.  The mineral wool is pretty tempting for it’s ability to drain and dry, but I am hesitant about it’s compressibility.  Does anyone have any guidance regarding Comfortboard 80 on a roof?
Is the location of the furring strips on the roof correct?  If I attach an eave in the manner shown, do I worry that the back plywood will rot from moisture?
I think the outboard most layer is an OSB with insulation Zip type panel.
I need to also mention that the whole roof is cathedral style.  I just mean there is no attic space.
Am I reading the right articles?  Barking up the right tree with this approach?  Thank you for your attention.

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  1. Expert Member
    Akos | | #1

    I have built pretty much your roof stackup with vapor impermeable underlayment. Used fiber faced polyiso with permeable underlayment for the roofing so the assembly can dry to the outside. Important detail here is to have enough exterior rigid for condensation control in your climate (40% of overall R value) and no interior vapor barrier on the ceiling.

    You could use exterior rigid MW but then you need to fully vent the roof which adds complication.

    P.S. VP100 for the walls is a bit overkill unless you use board sheathing. I would use one of the systems with integrated WRB and tape the seams or CDX with seams taped and the WRB over the foam. WRB over the foam with outie windows makes it simple to detail and build.

    1. RidgeHouse1950 | | #2

      Great! Thanks for the information. I did read a couple of articles on here about the percentage of exterior vs interior insulation. I plan to follow those guidelines. I just started sheathing, so I still have some time to change the plan, but I didn't spring for the Zip.

      Do I need the furring strips on the roof?

      Were you happy with that house?

      I'll avoid the MW, thank you.

      What do you like for taping the seams on the CDX?

      What WRB did you use over the polyiso?


      1. Expert Member
        Akos | | #4

        It was a metal roof so used horizontal 1x4s directly over the rigid. This was mostly to save the 2nd roof deck not for venting. If you are in heavy snow country (more than 50lb snow load), you want top venting with 2x4 furring.

        I used 3m8067 tape for the CDX. Could also use Zip tape. Whichever you can easily source. Make sure to roll it whichever way you go.

        WRB location depends on how you do your windows. I find outies on simple picture frame bucks around the rough openings with the WRB over the foam the simplest. This keeps everything in a single plate so there is no flashing tape origami by the rough openings and as close to a "standard" install as you get with thicker exterior foam.

        You can use any house wrap, I like Tyvec Commercial Wrap as it is thicker plus comes with a convenient grid printed on which makes finding studs and rain strapping install much easier.

        Nice part about the peel and stick over the roof is once that is on the place is dried in, gives more time for the exterior rigid or roofing is install.

    2. RidgeHouse1950 | | #3

      Also, I've never been known to underkill anything.

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