corrugated metal re-roof on barn

Guest User
Hi, I am contemplating re-roofing my barn, which has a 40+ year old galvanized corrugated metal roof on it. The existing roof is laid directly on purlins on about 3' centers with no roof deck. The existing metal sheet is not in super bad shape, but is definitely pretty rusty in some areas, and is curling up in others. Would it be ok to anchor 2x4's or other strips to the existing purlins over the existing roof and overlay the new roof over it? I think the existing roof is still plenty strong enough to walk on, and it seems like that would make installation much easier than tearing it off and only having the purlins to get around on. If an overlay is ok, would i get sufficient ventilation between the roofs by just putting a ridge vent in the new roof? What gauge metal should I try to get? 26 Gauge seems to be the heaviest anyone is stocking locally that I can find (Ft. Worth, TX). And finally, will galvalume or G-90 give better long term corrosion resistance? Thanks very much for any advice anyone may have! Nick
Todd Miller
Isaiah Industries, Inc.
Hi Nick, Thanks for your question. Obviously, I cannot say much in regards to the structural abaility of your roof to handle what you're proposing. If you feel it is necessary, I suggest having a structural engineer review things. They would probably do that for a couple of hundred dollars which could be money very well spent, whether it helps avoid a problem or just confirms what you're doing. Overall, what you're proposing sounds okay to me. You need to make sure that the high ribs in the current roof are strong enough to support what you're doing. However, I would work in some venting down at the eave to act as intake. The ridge vent functions as an exhaust but you need an intake at the bottom. As far as the gauge you're suggesting -- 26 gauge is certainly very proven for the type of panel you're talking about. As far as galvalume versus galvanized, that is an issue which I do not feel comfortable addressing in a public forum through the Metal Roofing Alliance which is an association of competing companies. I would suggest going to individual product manufacturers directly for that type of comparison. All best.
Guest User
Hi Todd, Thanks very much for the words of wisdom! I will do some experimenting on the barn this weekend and be sure the ridges on the existing panels will stand up to the load, and will definitely be sure I allow for air intake at the eave on the final product! Nick
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