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Advice needed on using recycled corrugated steel roof panels

Advice needed on using recycled corrugated steel roof panels


Old 04-22-14, 11:46 AM
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Question Advice needed on using recycled corrugated steel roof panels

I purchased some gorgeous (to my eyes) old corrugated steel panels that came from an old lumber mill here in "Gold County" CA, and want to use them as a roof for my 12'x20', 4x12 slope, gabled garage addition. They have some rust, but are the old thick stuff and should have plenty of life in them... and we love the look. Concern about water tightness led me to put 3/8" sheathing over my 2x4 rafters (2' apart). I have stapled down an underlayment (thinnish tar paper stuff). I'm now looking at my metal sheets and realizing that a. They are dinged up... not all straight and clean, especially at the edges, b. They have more holes than I thought...

Concern: leakage. The panels won't overlap tightly without a lot of convincing, and I need to seal those holes.

Complication: I sort-of underbuilt the roof structure... 2x4 rafters, and 3/8" plywood is too thin to attach any roof to without support. (I did brace the rafters at the plywood seams, either 4' or 8' apart, and think I did a decent job of framing the room structure.) But my paper was leftover from some long-ago roof replacement... It was in fine shape but is clearly the cheap stuff.

Question: Should I put purlins across rafters (over the paper)? If so, I think I will have to put "spacer purlins" above and in-line with the rafters so that I can screw down the edges. I have the expensive rubber grommeted screws, but will likely need a bunch more at this point.

Or can I install the panels right on top of the paper? If so, I will have to "prep" the underside of the panels so that I don't tear up the paper, and probably will have to install some "under purlins" beneath the sheathing... maybe a lot of them... because 3/8" ply isn't thick enough to hold the screws, right? Either way, I worry that the panels will leak, and the old paper won't hold back the moisture.

I am tempted to install roll roofing, or maybe some other waterproof material over the paper, and then put the steel over that ... but I'd have to penetrate the roof to attach the panels, and have more purlin decisions to make. Either way I worry that it would leak.

Please help. The panels seemed like a good idea, but I may have painted myself into a corner.
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Old 04-22-14, 04:02 PM
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One option though expensive might rolled membrane that is used at roof edges and valleys to protect against ice dams. It's good because it seals around nails driven through it to maintain the waterproof layer.

Another option might be to get good, straight roofing. If you get the painted type you could go with a color that looks like galvanized. Then get creative painting to give it a weathered look. Or if you get galvanized panels they can be weathered with acid & salt.
Old 04-23-14, 05:03 AM
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While I've never personally done it, I've seen new metal roofs that were faux painting to give the illusion of an old weathered rusty roof. As thin as some of the galvanized roof panels are today I'd be leery of using acid/salt.

If you're set on using those old roof panels, I'd work at straightening/bending the metal carefully where they join and use silicone caulk under the joints to help get a better seal. I'd also caulk every nail hole that isn't being reused. If you don't install strapping over the plywood you'll need to make sure the metal is secured to the rafters as the plywood isn't thick enough to hold the metal securely.
Old 04-23-14, 09:22 AM
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Thumbs up Updated project plan

Thanks so much for your thoughts. I spoke with an experienced "gold country" roofer yesterday who felt I was over concerned about the corrugated panels leaking. He suggested a good gook to plug holes and seal edges with, and confirmed that yes, the panels move on the roof, but that my 12' lengths were actually rather short, by barn roof standards, so it was less a concern than I was making it.

The 15# felt I tacked down needs to be stapled all the way around, then they'll be safe to walk on. Another layer would be good, but he doesn't think the miracle plastics (one called Tiger Paw was particularly attractive... $89 to cover my roof) are necessary, and might not tolerate the abrasion of the metal.

He suggests another layer of thicker, traditional 30# felt, (2x$28) which I was shy about because it is so heavy, but not if you cut it into 12' lengths on ground, which is the recommended procedure on UTube anyway... like lizards they need to lay out flat in the sun.

As for the long edges, Roger reminded me that recommended procedure for corrugated is to "overlay two humps ... everybody wants to cheat and just do one." He also recommended some gook named "Vulcan" or similar to put in the seams, but warned that the panels may become joined at the hip forever, which can hinder downstream repair/upgrade options. I will live with that.

I expressed concerns about falling off the roof, and Roger reminded me that constructing some scaffolding at the gutter edges is part of the job... and that this stuff really takes two people to do right, especially for a 59 year old rookie roofer.

So that's where I'm headed. Thanks again for helping me think this thru.
Old 04-23-14, 09:28 AM
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Thumbs up One more thing...

I'm also being told that my 3/8" plywood, altho a dumb choice for this project, will probably hold a good roofing screw. That diminishes my concern about putting purlins everywhere. I will mount the panels directly on the felt, but will grind off any jagged stuff on the bottom of the panels.

I will re-use the existing holes in the panels, which are on the top of the hump, as much as possible.

Two days before the next rain... gotta get on it.

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