Metal Over Felt Over OSB

Allan Bremer
Al
8/31/2012
I'm new here and I'm glad I've found a place where metal roofer professionals can answer questions. There seems to be so many different opinions about how metal roofs should be installed - it's crazy! I'm just wondering if I'm doing the right thing by having my metal roof installed in this matter: First of all, my roof is a 12:12 pitch - really steep. I've used 2x8 rafters on 24" centers and my place is only 20x30. I've used 5/8's osb and then I put #30 felt on it. It is a 1-1/2 story place with a loft and it's all a cathedral ceiling - no attic. My roofer says that the felt acts as a vapor barrier and plans to simply put the metal right on the felt. Other people have told me that the bubble wrap would act as a better vapor barrier and that I should use it because it will also dramatically decrease the temperature of the house in those 100+ degree days. BUT, I'm mostly concerned about condensation and my roofer thinks that because of the steepness of the roof I really don't have to worry about condensation and that the felt also helps with that. My main question is that I'm wondering if it's ok to simply put the metal right on the felt. I have attached an image of the inside of the build at loft level.
Todd Miller
Classic Products, Inc.
9/1/2012
Looks like a nice place you're building. Tell me a little bit about how the ceiling will be finished. Drywall with vapor barrier behind it? And then I'd like to know what insulation you will have and whether you will have any ventilation at all. More than anything, I am concerned about moisture inside the home condensing on the bottom of your roof decking.
Guest User
8/14/2017
Hi I have a garage whit asphalt shingles over OSB sheathing. Can I install the metal roof over the shingles and will the screws hold in the OSB
Info @windowsonwashington.net
An informed customer is our best customer.
8/14/2017
Yes. You will need to check with the metal panel manufacturer but most will require a slip layer to protect the back side of the panel from the shingle granules and abrasions.
Todd Miller
Classic Products, Inc.
8/14/2017
Allen -- a couple of things to consider. 1) Some metal roofs will be more likely than others to "telegraph" any unevenness of the surface beneath them. 2) Fastener pull out all depends on the condition of the OSB. Screws will do better than nails. You can test fastener pull out resistance ... I would look for a minimum of 50 pounds of resistance per fasteners, and preferably higher than that.
Guest User
8/25/2017
So living in Seattle area will I be OK to install my R pan roofing right over the synthetic felt over the osb? I will have 6/12 pitch roof with 12" of blown in insulation. I've been given advice for and against furring strips.
Todd Miller
Classic Products, Inc.
8/25/2017
John, that sounds like a pretty typical installation. Do you have attic ventilation? Is your OSB in decent shape?
Guest User
8/25/2017
Yes it is new construction and meets all ventilation and insulation requirements. Thank you for the clarification as I wasn't really wanting to install on Batts due to sagging from snow when it does happen!
Todd Miller
Classic Products, Inc.
8/25/2017
Sounds like you are in good shape to move ahead as planned.
Guest User
1/6/2018
Hello there,I am about to have a contractor put on a metal roof on my house in central florida.he is going to removing the old shingles,then placing a moisture barrier on top of the osb then the metal roofing .i have seen many other contractor use 1 x3 strips on top the barrier , then metal which i think is stronger because the 1 x 3 strip are screwed directly to the rafters every 24 - 36 inches.my question which is better / stronger strips or no strips.?.thanks-homeowner.
Todd Miller
Classic Products, Inc.
1/6/2018
Sam, I get asked this question a great deal so I have created a video and blog post to address it. You can link to it here: https://www.asktoddmiller.com/roofing-help-videos/metal-roofing-101/metal-roof-installed-battens/ Feel free to post back with any additional questions.

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