Retrofit continuous insulation over roof; how are gutters attached
We are putting 2″ of continuous insulation above the roof line; we had hoped to do TimberBoard but that’s not available yet, so it’s going to be polyiso.
Inside to outside stack: existing sheathing, wrb, foam, standing seam metal roof.
Plan was to leave existing fascia in place and cover the edge of the foam using drip edge with extra long vertical leg. Then the gutters can be top-fastened into the existing rafter ends/fascia. But that would put gutters low on the fascia.
Roofer suggested adding a perimeter of wood at the eave (like 2×2), above the existing fascia, then flashing to cover that and regular length drip edge. Idea being that gutters could connect to that. I’m a bit worried that water (getting under the metal somehow) would hit that 2x perimeter and stop …
So I guess I’m asking: Can the secondary drainage plane/WRB be at the sheathing but the gutters fastened above that to match the primary draining plane (the metal roof drip edge).
Anyone got links for details for foam above sheathing that might help here? See quick hand sketch. Question is about the area where the question mark is 🙂
Thinking perhaps a strip of Cor-a-vent underneath the 2x perimeter fascia extension, to still let water drain from the WRB?
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Replies
James,
The roof underlayment over your foam is your secondary layer of protection against leaks. It should overlap your drip-edge, and it doesn't make much difference if the material at the perimeter is foam or a 2" high wood perimeter in terms of preventing water damage or facilitating drainage. I'd do what the builder suggested.
Thanks. I think the roofer is planning to have the foam above the underlayment.
That’s why I think the secondary drainage plane is at the old sheathing layer.
What I have done is beveled the edges of the 2x to match the slope of the roof. This gives you a nice flat surface for attaching things. You should do this on all edges to protect the foam from critters.
Underlayment should go directly under the panels, having an extra one under the foam is not an issue.