preparation of roof before strapping

Guest User
1/24/2005
Hi, I was wondering if anyone could answer my question. It is ok to have the strapping nailed on top of the old asphalt shingles and no underlayment or plastic installed. Will this affect the life of the steel roof.
Allan Reid
Dura-Loc Roofing Systems, Inc.
1/25/2005
The building code states that all roof products shall have an underlayment which serves as a moisture barrier in the case of severe weather and to deal with any condensation unless a product is tested and approved otherwise. Plastic is not an approved product for this purpose. Choose a product and contact the manufacturer to get their recomendations and also ask to see their product approval report which will indicate that it has been tested and approved to install over existing roof material and how to install it. Then if you are worried about the life of the roof ensure that the base steel is a G90 galvanized if painted or AZ50 bare. Choose a good coating system such as granular, PVDF or SMP.
Guest User
1/25/2005
Hi Allen, I spoke with the company that makes the metal roofing and they said that it was ok to put strapping over the old shingles and their was no need for underlayment. The warranty the roof for 25 years if installed this way. I am wondering if their is still a consern for moisture or condensation problems inside the house. The house is a viceroy stlye home with vaulted ceilings. There is good ventilation and insulation in the roof. I don't have any moisture problems with the asphalt shingles should I be concerned with the steel roof if there is no underlayment. I am not sure if the building code is different here in Canada.
Allan Reid
Dura-Loc Roofing Systems, Inc.
1/26/2005
I stand by my last advice. Ventilate, underlay.
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