I've got a barn that is due for a replacement of the old corrugated metal roof. The old 1/2 inch corrugated metal is rising through or edge torn by high winds in some places. I am looking at 3 options:

Going to heavier gauge 5v which will last longer and is sturdy enough to walk on to clear stuff off the roof as needed (leaves/branches). 2x the price.
Sticking with corrugated 1/2" and either replacing what is up there now, or perhaps just pulling up the screws and putting the new over the old in a double layer.

I see some pros and cons to trying 2 layers, new over old:

Con: It may be a pain to drive screws through. It will be twice as much weight up there, but I'm not really in a snow zone. The old metal will theoretically still keep rusting underneath though perhaps more slowly. Still have to take out the old screws.

Pro: don't have to remove old roof itself. Double layer should be sturdy enough to walk on without having to use plywood pieces to distribute weight.

I've never heard of doing this and I think there might be a reason for it but I really dislike not being able to get up on that roof as needed and easily brush off debris to keep it from rusting out faster.

Replace it.

We did that once on an old cabin we had. It was a pia to get the old screws out. Some heads broke off so we had to get them out with lock pliers because the shanks would be against the new roof if we didn't.
What wasn't good was the roofs would sweat and get moisture between them and caused the underside of the new roof to start corroding…..and it was galvanized.
We didn't know that till we had to pull up a piece because of a leak.
I don't know the long term results on the roof as we sold it about two years later.

We put Q decking on barn and hay barn as well as original ranch house. I was a mere lad in 72 but along with a neighbors 16 yo son we were able to jump that stuff up. Just replaced the house due to some well placed hail hits that cracked it in a few seconds it's. It was over 50 years old. Barn roofs are both hanging in still although it's time for Ospho and a paint job. If I knew how to lay it out, I'd paint a Texas flag on roof. For fun.
Anyhow, it's more durable than what you get at Home Depot. But once, cry once.

It's a barn, you can do whatever you want, but I'd remove the old. For my old barns, if the metal roofing is bad enough to warrant replacement, I would remove it because there is guaranteed to be rot under it that I might want to fix. Maybe my rafters are rotting, or the purlins need work. I'd personally remove it first. Plus, even if you match the profile, it's going to look funny.

I'd replace with 26 gauge R Panel as it's more common and easier to source. I havnt seen corrugated panel that is as beefy as the stuff on my old barns. It's a lot of work to put on a cheap product. Mueller will have what you need as will any decent supplier.

If this is something that you don't ever want to leak, then consider snap lock panels.

Then sell your old roofing on nextdoor for twice what you paid for your new roofing to someone who wants rustic kitchen decor.

Yeah, that was my concern that all the metal to metal contact if there's even a little bit of difference in the metal and galvanized coating composition and it gets condensation then it makes a galvanic cell and rusts out really fast. So my real choice is to do a 10 year job with the crappy 30-31 gauge 1/2 inch corrugated they make today, or use the 29 gauge 5V that seems to be a little bit more durable and at least easier to walk on if needed with the flat spots.

FWIW, I'm still able to buy 24 ga and 26 ga 7/8" high-cor metal roofing in 36" widths. It's manufactured in Temple Texas by Metal Sales and I'm able to buy small quantities from Pioneer Steel (Bryan and Waco).


7/8" Corrugated Roofing

This stuff is the old-school roofing that barns used for years, and you can walk on it without bending it.

Would I use it on a new install? I dunno. But for repairing/replacing old stuff (like corrugated fiberglass skylights that crack out) it does the job.

Sound wisdom. Good post sir.

Gunny456 said:

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We did that once on an old cabin we had. It was a pia to get the old screws out. Some heads broke off so we had to get them out with lock pliers because the shanks would be against the new roof if we didn't.
What wasn't good was the roofs would sweat and get moisture between them and caused the underside of the new roof to start corroding…..and it was galvanized.
We didn't know that till we had to pull up a piece because of a leak.
I don't know the long term results on the roof as we sold it about two years later.

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it will corrode even though galvanized. The metal we sold and the Lumber/Hardware store I worked at for years came from the manufacturer with a thin sheen of oil/protectant on it while it sat in the racks for sale. I have sat pieces out on blocks to use for stuff down the road and it would corrode as well.

Yep. It was corroded between the two.

My experience goes back 50+ years. My dad was a school teacher. In the summer, we would build and repair hay barns, mostly pole barns. Several times we did just what you're describing, putting new tin over old, at the owner's request. This was long before screws and cordless drills when we still had to use leadhead nails. Driving a nail through four sheets of tin at a corner was lots of fun, especially in July and August. We used Vicegrips to hold the nail to keep from smashing fingers.

Not sure how it held up.

I'm going to pull it off as I go. The roof happens to be 36x16 each side of the ridge so 24 of 16x3 R panels is what I just bought. 26 gauge galvalume, with the coating that resembles a bare galvanized tin. Should be fairly easy to keep alignment with just a single row of long panels for each side, and it'll last a long time.

Either way the purlins not spaced too far, I should be able to walk on the new panels as I work my way across after the first one is set.