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location of ice-and-water membrane

tadumbleton | Posted in Energy Efficiency and Durability on

I’m renovating a 1966 wood frame with partial cathedral ceiling in upstate NY (climate Zone 5).  The original house had cedar shingles over deck with 1″ foam insulation.  I want to replace with the following from outside to inside

metal roof (standing seam) new
roof deck board (zip) new
furing strips new
4″ Dow Tuff-r (2 layers x 2″) new
ice and water (new Grace)
existing deck

Is this acceptable layup?  I was considering using Hunter Panels but they take a while to get, and I really need to get the cedar shingles removed asap.  Am I ok demoing that and putting on Ice and Water or is there a risk with Ice and Water that low in the assemblage.   Thank you for the advice

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  1. Expert Member
    Akos | | #1

    In zone 5 you need 40% of your roof R value above the deck for condensation control.

    So in your case with 4" plolyiso (~R22 LTTR), unless you have more than R55 bellow the rafters, the peel and stick bellow the foam is fine.

    Not sure if Zip will buy you much. Most metal roof manufacturers require a synthetic underlayment under the panels, the WRB coating on the ZIP is redundant. Regular plywood is cheaper and hold screws better.

    Provided there is no vent channel in bellow the old deck, your new roof should work very well. Make sure to stagger the seams on the two layers of foam. Taping them doesn't hurt, but also not required with the peel and stick bellow.

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