installing metal over old shingles

Guest User
5/19/2008
I thought the price of a new metal roof was beyond my means. But a contractor qouted a price for a metal roof installed over my old shingles.The savings in not having to pay for removal and disposal of the old shingles,put the price of a new metal roof just a little over the cost of a shingle roof. I am now considering this metal roof option. My roof is a 12/12 pitch,and has 5 roof windows. Should I have concerns, such as weight,or condensation ?? He said it would be installed on wood strips attatched to the existing 3/4 inch plywood roof sheeting and would have a ridge vent as well as soffit vents. Is this type of metal roof installation ok?
Nate Libbey
5/20/2008
Many metal roofs can be installed in this way with no problem at all. The fact that the roof will have ridge and soffit vents is definately important. If you have more than two layers of asphalt shingles I would check to make sure that this is allowable by your local building code. Some codes do not allow this. Being installed on wood strips will allow for some air flow under the panels, which can help prevent condensation.
Todd Miller
Isaiah Industries, Inc.
5/20/2008
Thanks Nate. Always verify, too, that the product is being installed in accordance with manufacturer instructions.
Guest User
7/1/2009
When applying purlins, should I used galvanized screws, regular wood screws, stainless steel screw? Also, how far should the screws extend through the existing roof? Thanks for any advice. Love this site! I've been reading through the Q/A's now for hours!
Todd Miller
Isaiah Industries, Inc.
7/4/2009
In many cases the purlins are nailed down. The fasteners should penetrate or at least extend 1" into the roof decking. You can also if possible use longer fasteners and attach the purlins to the trusses.
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