Guest User
7/19/2017
We currently have a cedar shake roof and are considering replacement with metal shakes. Present underlayment is 12" x 1"s with 4" spacing between each. Is it possible to install the metal shakes with this configuration or will we have to add seamless plywood, for example. As an alternative would it be possible to install over the present shakes. Many thanks for your assistance.
Todd Miller
Classic Products, Inc.
7/19/2017
While there may be some products that technically can be installed over spaced boards like that, I never suggest it for residential applications. Exposing the back side of the metal to the attic (even with underlayment in between) is a real invitation for condensation issues. My recommendation therefore is to either fill in the gaps with dimensional lumber or install solid decking over the boards. As far as going over the old wood shakes? There again, there are some products that probably would be approve day their manufacturers for doing so, but I advise against it. I am concerned, even if it does work from a technical and functional standpoint, that at some point in the future, a home inspector working on behalf of a mortgage company / potential home buyer, may take exception to what was done.
Dick Bus
7/19/2017
I agree with Todd. you are better off removing the cedar roof, filling in the gaps or installing plywood, installing good quality underlayment. Now would also be a good time to make sure you have a balanced ventilation between the soffit and ridge. thanks for considering a metal roof.
Info @windowsonwashington.net
An informed customer is our best customer.
7/20/2017
+1 I would definitely look at making the necessary decking adjustments as the two gentlemen stated before. These guys are pros in their industry for a reason. Solid decking (perhaps even plywood the whole deck) and ventilation are critical. You are putting down what should be a permanent substrate. Make sure the rest of the equation is engineer for permanency.

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