EddieWalker
Epic Contributor
I am amazed, not really, on the disagreement amongst installers on the best way to install metal roofing panels on top of sheathing. So what does TBN folks have to say. Existing construction not changing so not allot of value in this thread to discuss why it is better to not use sheathing under metal roofs in the first place.
1/2" ZIP OSB sheathing, metal panel approved 1st layer moisture barrier.
I was going to just screw the panels to the roof, hitting the 24" OC rafters if needed, however this method seems to cause a great amount of gas buildup if you google on the internet. Their preferred solution is to screw 1x4" strips to the sheathing to keep the metal off the roof which they believe will prevent moisture damage from condensation. Thinking this through, a problem of mine, any condensation will still end up on the sheathing so I do not see how this is a solution any better or worse than screwing it directly to the sheathing. Actual experience greatly appreciated, opinions will be tolerated.
First you have to decide why you are using metal for the roof. The most common reason is that it's the cheapest roof you can create when using purlins across trusses or rafters. It is fast, easy and it will last a very long time. If you are just wanting a roof over something to keep the rain off of it, then this is the best way to go based on price.
If you want a metal roof over a house, it's very common to use decking under it. It's not required, but it does give you that extra amount of strength, and another barrier to keep water out. The decking has to be either ZIP system with tape, or you have to put felt paper over it. Moisture will form under the metal and it needs a way to either drain out, or just sit until the air flow dries it out. I had a job once where I added a metal roof over a deck that I built and attacked it so that it went under the existing metal on the roof. Water flowed from the roof to the deck like it was supposed to, but every morning, and after a rain, water would drip out under the roof where the deck started. It took some time with a hose on the roof, but I figured out the gaskets on the screws where leaking and allowing water under the metal that flowed down over the top of the felt paper on top of the decking.
I'm curious what you mean about gas build up? There should never be any type of gas in an attic, or anywhere in a house that isn't properly contained.