Guest User
5/28/2013
I have a customer that had a couple questions I haven't heard of before. He is planning on re-roofing a 3/12 gable roof. The plan going forward is to tear off the old shingles, lay down felt paper and than strip it with 1x4 pine screwed to the trusses with Propanel II from Metal Sales. His first question was worry if the felt would be broken down from the heat of the steel and if he should use a hightemp synthetic felt? Second question, he was told if he puts the steel on purlins he needs to insulate the gaps so the steel doesn't rust from underneath. Am I missing something that I should have been doing all along? Thank you very much for your help :)
Todd Miller
Isaiah Industries, Inc.
5/29/2013
Thanks for your question. I would always suggest contacting the roofing manufacturer but let me give you your thoughts as well. Without direct contact between the underlayment and roofing, a high temp underlayment is not necessary. That said, I would suggest either 30-pound felt or a synthetic underlayment as well as ice and watershield as required by code. Generally speaking, the best way to avoid rust will be to have an airgap under the panels rather than fill that with insulation. That said, there is very little risk of back side rusting any way as long as all else has been done properly.
Guest User
5/29/2013
Thank you :)
Eric Novotny
An informed customer is the Best Customer!
5/30/2013
+1 Make sure you still run I/W per code. High temp isn't required and I would run synthetic like Todd said. Larger sections, less seams, more secure to walk on. Having the roof with overdeck venting would larger eliminate the condensation potential as well as he synthetic underlayment (polypropylene) being a class I vapor retarder. The sheathing doesn't need to breathe but the roof (if vented design) does need to.
Dick Holcomb
5/30/2013
Will adding a new metal roof over the existing shingles on top of 1 x 6 boards cause the existing 5" gutters to be raised because the roof line will now be higher? One installer said the answer would be to wait for a heavy rain and see if the existing gutters catch the water flow off the metal roof, and if not to install 6" gutters which will solve the problem. My 5" gutters are aluminun and in good shape so i hate to go the extra expense. Any thoughts on this subject would be appreciated. Thanks-
Todd Miller
Isaiah Industries, Inc.
5/30/2013
Dick, my recommendation is 6" gutters mounted as high as possible. That said, you could probably get by with just raising your 5" gutters but I do think they will need to be raised.
Eric Novotny
An informed customer is the Best Customer!
5/30/2013
+1 Depends on the angle of the fascia board, pitch of the roof, and type of drip edge/starter that is used. We normally see roofing and gutter projects go together thought so it is not something that normally presents itself as an issue.

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