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Do metal roofs require more or less ventilation than asphalt shingles? I have a roof with 8" styrofoam/OSB panels on 2X6 decking with approx. 1"X1" ventilation passages built into the panels. Is this sufficient ventilation? I also get a lot of expansion/contraction during the day. Which systems work best is such a situation>
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Generally speaking all roofs require ventilation equally as part of the building design. Ventilation must be of a certain size and balanced between the eaves (inlet) and ridge (outlet)to work the best. Gable vents are an alternate however you need larger areas.
The new building codes require that "catherdral" assembly roofs such as yours where there is no attic, have a 1 1/2" air chamber directly under the roofing material that is vented. The flutes you have are better than nothing provided the openings are not restricted at the eaves and ridge.
Most metal roof systems can be applied over a strapping which would allow you to incorporate the required air chamber and ventilation when you reroof and would give you the further benefit of applying it over your old shinglke roof which would then act as a good condensation barrier.
Hope this helps.
5/1/2002
Dura-Loc Roofing Systems, Inc.
5/8/2002