I looked at a 15 year old aluminum roof today that has corroded through in 5 or 6 places. Through the holes I can see the original steel deck which was left in places when the newer roof was installed. I’m assuming galvanic reactions ate through the new decking due to condensation between the layers. Am I right? Obviously a new roof is going on but is it okay to install a new steel roof over the original steel panels? I say no but the roofer says its okay.
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An awning of aluminum came flying off during a West Texas dust storm. The aluminum panels were still in good shape, but the installer used steel screws to put down the panels. The failure was seen where each and every steel screw/washer touched the aluminum and formed galvanic corrosion.... If the photo is any representation of the whole picture, your roofs may be too far along to do much else than total replacement of at least the top layer of panels; maybe both of them....
If you are in Florida... here's a company that is based there and makes a product that lets you keep your old roof panels on and add the new panels on top, allowing a space for air and condensation to get out of the ridge venting...
http://www.roofhugger.com/
In April, we had 30 minutes of non-stop golf ball size hail. The 14yr old R-panel was beatup pretty bad, but never had a leak. Insurance paid for replacement of a 14'x21' gambrel roof and a 30x52' gable-style roof with a 4/12 pitch. With some honest and greatly appreciated information provided from experienced members on this forum, I also went back with Kynar's Snow White panels sold from MBCI and Roofhuggers were installed on 4' centers. Except for about a half-day's of details, they were finished last Monday. As of Jan. 1st, that paint and color will qualify for "cool roof" tax credit of 10% of the material cost if it is part of your home. Scroll down until you see the topic "Roofing":
Bill
Edited 1/15/2009 10:49 pm ET by BilljustBill
Obviously, aluminum over steel doesn't work. And it would be best to tear off everything and start over fresh on the perlins.
Having said that-I have done a lot on rural agricultural buildings. Many farmers around here are only willing and/or capable of doing things as cheaply as possible. I have overlayed steel on steel several times, once back in '72 or '73. That roof was still going strong 20 years later, and I have no reason to believe it's not still on there now.
If you can afford it, remove both roofs. If you decide to overlay, make sure he uses screws long enough to reach the perlins. Don't rely on the old panels to hold down the new ones.
John Svenson, builder, remodeler, NE Ohio