New to this site but question about installing metal roof?

[Sonny]

New to this site but need some info. Which is best to install metal roof over plywood with 1x4 strips every 2' or to install metal roof right on top of titanium roof covering or what?  Need ideas! Thanks!

[Redoverfarm]

I put Titanium Felt under my roofing which was exceptable from the metal manufacturer.  Most metal roofs are laid upon ply and either #30 felt or synthetic felt. I used synthetic because it will last longer than 30# felt.   With 30# felt it can stick to the back of the metal sheets and when the sheets expand and contract it will tear the felt and could be a possible location for water penetration if a leak would occur.  Some of the experts say if you are going to use felt to lay a layer of rosin paper on top of the felt to act as a "slip" layer. Some suggest that if you are laying metal over shingles that purlins be used to level the roof but most suggest removing the shingles. Purlins are mostly for "Structural metal roofs" rather than "Architectural Metal Roofs".  Structural are made of a lot heavier guage metal whereas Architectural is thinner because it is laid upon a solid base rather than purlins.

Here is a few sites. Agreed they are company sites but do have some good information.

http://www.metalsales.us.com/files/installation-guides/Application%20Manual-West%20Coast.pdf

http://www.classicmetalroofs.com/docs/Insiders_Guide.pdf

[MountainDon]

What John said! I have a metal roof just like John described; metal over Titanium UDL and that over the standard roof sheathing panels. No purlins / wood strips.

[Sonny]

What size sheathing did you use?

[MountainDon]

7/16 OSB.
Over trusses 24" OC