what is the correct way to install metal roof

paul heckman
6/12/2011
I have a cabin with not 2 but 3 layers of existing "roofing" (1 layer of shingles and 2 layers of roll roofing). It has about a 6/12 pitch running about 50 feet long and 11 feet from peek to drip edge, it also has a porch area on each side with more like a 2/12 or 3/12 pitch area.I know the old has to come off and was thinking about metal sheet roofing but have read about using furring strips or not and just putting the metal right on 30 lb felt paper on the deck. I do not want the deck to rot out, but there seems to be no right or wrong way with "experts" saying both are ok. Will either way work, one better than the other? How do you make the transition from the steeper pitch to the shallower pitch, will flashing cover it, how far should it go over the lower section to prevent snow/ice from backing up under it? Would the flashing match the ridges in the metal roofing? Thanks for any help.
Todd Miller
Isaiah Industries, Inc.
6/12/2011
You will need a pitch change flashing as well as ridge flashing. There should be closures or a Z Channel available to close in the roof profile where it meets the ridge. You do not have to install over furring strips. Installing direct to deck with underlayment works very well. Furring strips, which can be used with some products, would help summer energy efficiency. I would advise using this time to also take a look at your attic ventilation and see if it can be or should be improved.
Eric Novotny
An informed customer is the Best Customer!
6/13/2011
Given the temperature extremes and likelihood of condensation in these type of conditions, I would echo Todd's recommendation to examine the attic ventilation and insulation. If you use a system of furring strips to attach the new roof to the old, you could create an over deck venting system and potentially eliminate some of the ice damning problem. I would also encourage you to look critically at the attic insulation and see if you can eliminate the source of the problem (ice damning) altogether.
Todd Miller
Isaiah Industries, Inc.
6/13/2011
A couple of additional notes ... I'd missed your reference to ice and snow earlier. A real key on pitch change flashings is to make certain they are mounted high enough on the upper roof that you are able to maintain positive pitch on the flashing. The flashing should go up under the upper roof by several inchues and also have extra underlayment work in so it goes under a higher section of underlayment. The transition flashing should come out on the lower roof by at least 4 - 6" and also have a Z channel ir other flashing or method of keeping ice and snow from backing up under it. And, absolutely, if ice has been a problem in the past, take a hard look at insulation and ventilation in the attic.

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