Our cedar roof needs to be replaced. It's on skip-sheathing (1x3s spaced 7.5" on center). The roof has a 6 in 12 pitch. The house has no eaves and lacks soffit vents. Instead, for intake, there is an approx one-inch gap above the fascia board, except in the rear of the house, where the cedar fascia trim totally blocks the gap. There are hip and ridge vents.
I've been told by one roofer that a metal roof can be installed directly onto the skip-sheathing without solid decking, but I've read opinions to the contrary, mainly pointing to condensation issues and differential pressure issues which could cause the roof to "wiggle" slightly which, with time, would lead to leaks.
I am willing to pay a premium for a roofing material that offers longevity, but I would like to avoid spending thousands on solid decking if it isn't really required. Would 24" wide solid decking at the eaves, with ice guard, be OK, leaving the rest of the roof as is with the spaced 1x3s? Is there an inexpensive solid vapor barrier that can be tacked to skip-sheathing?
We could address the ventilation issue, where the rear side of the roof has no intake vent, by using an under-shingle "smart" vent with a one-inch continuous slot cut into the eave decking six inches above the drip edge.
Guest User
2016-12-12 22:07:13.000000
As a general rule, I do not recommend metal roofs on spaced sheathing for residences, especially not when ventilation may be limited, when we do not know whether there is a vapor barrier behind the ceilings, and when the house is in a condensation prone environment. You have at least two of those three factors.
I would install solid decking and look for ways to increase ventilation.
The risk is that warm moist air originating inside the home migrates to the attic and condenses on the back side of the metal panels. This is worst during spring and fall seasons when ambient moisture levels are often high but it gets cool outside at night.
Proper ventilation requires a balance of intake vents and exhaust vents. Intake vents are usually in the soffits with exhaust vents at the ridge.
Your metal roof manufacturer may have some ideas on a vented eave detail that would help supplement your intake vents.
Todd Miller
2016-12-13 05:27:21.000000
+1
Both the avoidance of condensation and the quality of the install make solid decking a great choice here.
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