metal over existing shingles

Guest User
4/24/2016
I have an existing asphalt shingle roof that is 17 years old (original roof on home built in 1999). The roof has lost some shingles during high winds, the shingles are somewhat brittle, and some have few if any stone granules remaining. I am considering a metal shingle roof, and a contractor suggests installing metal shingles over existing shingles with no underlayment between asphalt and metal shingles. Is this approach reasonable? Does the condition of the asphalt shingles have any impact on the acceptability of this approach?
Info @windowsonwashington.net
An informed customer is our best customer.
4/24/2016
He would be wrong in that case. You need a slip layer at a minimum to protect the back of the panel. I prefer to just go ahead and remove the roof, but going over the top is acceptable as long as you address the underlayment/slip layer minimums.
Guest User
4/24/2016
Thanks for your reply. Since i'm not a roofer, this can be confusing stuff - some manufacturers and contractors say no underlayment, some say underlayment. Just trying to get as many opinions as I can before making a decision on a big expense.
Info @windowsonwashington.net
An informed customer is our best customer.
4/24/2016
I don't know who is saying no underlayment, but if you are putting the roof direct to deck (i.e. not on purlins or battens) it absolutely most have a slip layer. If you are putting them on some sort of purlin/batten, the slip layer is not required but most will put down an underlayment prior to the purlin/batten.

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