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I am hoping to "replace" the existing asphalt shingle roof on a log home with a standing seam metal roof. One contractor I've spoken with tells me up front (without actually seeing the house) that he recommends a tear off of the existing roofing in any case on such a replacement. Another contractor has been out and told me there's no problem with installing standing seam over battens in my situation.
1. What's the conventional wisdom on this issue?
2. It would seem to me installing over the existing roof using battens creates a dead space between the old and new roofs. The house is in the woods in the Smoky Mountains of NC, and moisture is an omnipresent fact of life (moss on the existing roof has been an ongoing problem for some time now). Would condensation under a "battened" metal roof be an issue, either long or short term?
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First of all, #1 rule: Make sure that, however you install the panels, your installation method is approved by the roofing manufacturer.
Some metal roofing systems are designed to be installed over battens, some over decking, and some over both.
Many systems, including the shingle, shake, slate, and tile look products, can be installed over old asphalt shingles as well, with appropriate underlayment.
I am a strong component of proper attic ventilation. That should be taken into consideration on any building with any type of roofing material.
If you install over battens, you will not experience any increased condensation concerns. Yes, condensation can occur on the back of metal roofing panels due to certain weather conditions. With battens, there is added space for fast evaporation. This can be enhanced by putting down vertical battens first followed by horizontal battens so that this space can even be ventilated from eave to ridge. This airspace can also help significantly with energy efficiency of the roofing system.
To sum up, there is no "right" answer to your question other than making sure that the metal roof you choose is installed according to a method approved by its manufacturer.
6/4/2004
Isaiah Industries, Inc.
6/5/2004