Questions about metal roofing

[cactiki]

Hi garage people. Well, it looks like I can finally fix the garage roof, so now i have a few questions. I am planning to go with pbr panels because I don't want to ever do this job again. I have a 33' x 26' roof which previously had rolled roofing on it. I say previously because it is all gone now! Over the last few years (ok 18....) it has all been blown off by our Mojave desert winds. Fortunately we only get about 5 inches of rain per year, but still a lot of the plywood sheathing is in bad shape because it has been exposed to the elements. I have been trying to research this online but still am not sure the best way to go, so here are my options:
1: remove and replace all sheathing, then attach the metal to the plywood, with a vapor barrier between them.
2: leave the sheathing in place, and run stringers of 1 x 4 (or 2 x 4??) horizontally, 24" on center. This way I could put fan fold insulation in the space between.
I am wondering if there is any reason to remove the sheathing and replace it. It is not going to fall in on me, but it is weak enough I wouldn't want to walk on it or attach my metal to it. If I use 1 x 4s, will it be strong enough to walk on? What about 4" wide strips of 3/4" plywood, wouldn't that be stronger? And can you walk on a roof of these metal panels? They seem like they would bend. Does anyone know of a good website about installing metal roofing? Any thoughts, suggestions, or recommendations? Thanks for reading and hopefully responding to my post.

 

[LutzTD]

sounds like a flat roof. Most metal roofs want a minimum 4:12 pitch. I dont know if that applies for 5"/yr of rain but would be a good question to ask

 

[cactiki]

Sorry, I forgot to mention it is not flat, I think it is about 5:12

 

[VinDSL]

I live in a high-wind area too - been fighting asphalt shingles for years (supposedly good to 125 MPH).

A couple of years ago, we got prolonged high winds with 90 MPH gusts (measured at the airport), and it ripped about 1/4 of my shingles off (but it left most of the paper/vapor shield). Other ppl, in my neighborhood, actually had their entire roofs blown off their houses -- plywood and all.

We were declared a "crisis area". Insurance companies called in extra adjusters. Took 3 months before I could schedule a roofing company to make repairs - they were so busy. As it was, I had to use a roofing company from a town that was 80 miles away.

Anyway, that did it for me. I went with $8,000 worth of pbr panels.

The roofing company said they could strip off (what was left of) the old shingles for $1,000, but they said they prefer to lay the metal panels on top of it -- better insulation, they said.

Looks great. Haven't had a problem since.

And, yes, you can walk on it (don't step on the peaks). Just make sure to use soft-soled shoes, like tennis shoes, gum rubber soled deck shoes, or whatever.

 

[mebedave]

will someone explain to OP how to use a vapor barrier

 

[bob15]

I have a barn with a 12:12 pitch with asphalt shingles and wood shingles under them on half the barn. To strip would be getting a dumpster for material removal and buying plywood, plus tar paper and singles. I went with classic 5 rib metal roof. If you run 1x4's across the old roof at 24oc, you will be fine. I used screw for fastening and metal roof sealant between the joints, although on another roof I have I used double-sided eternabond RV roof tape for seems.

http://www.metalsales.us.com/files/Tech%20Center/Product%20Manual%202011/Classic%20Rib-2011.pdf

bob