How do I install a metal roof over a shingle one?

Guest User
9/29/2002
How do I install a metal roof over a shingle one and what material do I need?
Todd Miller
Classic Products, Inc.
9/29/2002
Thanks for thinking metal! This is a very broad question. With most systems, you will first install underlayment followed by eave and gable trim. The field panels install next, completed by ridge and hip cap and other flashings. The best thing you can do is to find a product you like and then address these questions to the manufacturer.
Guest User
10/4/2002
We are in the process of getting estimates to install metal roofing on our house. The house currently has fiber glass shingles which are about 13 years old, but in good condition. One contractor tells me that since the shingle are in good condition, we can install directly on the shingles. Another contactor tells me that we need to lay down 1x4 firring strips on 2 foot centers and attach the metal to the strips. The main reason for doing this is to provide air circulation under the metal. Another contractor said we should lay down 30# roofing felt over the shingles prior to installing the metal roof. I'm very confused at the moment. What do you recommend? Thanks.
Todd Miller
Classic Products, Inc.
10/5/2002
The good news is that everything you've been told is true. Okay, let me explain a bit. First, I would install an underlayment over the old shingles. It is just an inexpensive safeguward which can dramatically improve the long term performance and value of the entire roof system assembly. Next, several metal roofs have been designed for installation over existing shingles, no battens. With many metal roof systems, this works just fine and does not jeopardize anything. Other metal roof systems are designed for installation over battens and, with those systems, battens need to be installed. This would primarily be some of the aggregate-coated and painted steel tile facsimile products. Other systems would likely perform best over battens but can be installed over decking as well. These would be primarily some of the through-fastened "sheet style" steel roofs. Being installed over battens will extend those products lives by allowing ventilation beneath them. When installing over battens, regardless of the system, I suggest a "grid" of vertical battens followed by horizontal battens. Horizontal battens only will impede airflow and cause problems with trying to take advantage of ventilation beneath the roofing. Consult with the manufacturer of product(s) you choose for detailed information on battens vs no battens, etc.
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