Adhesive and Sealant for Problem Screws on Metal Roof
ylekyote
| Posted in Energy Efficiency and Durability on
I have a u-channel metal roof. The washer screws that go through the roof into the plywood and rafters are backing out dozens a year and many are stripped. I want to tighten or replace them as needed and use something to keep them in as well as seal the threads and gaps watertight.
Any suggestions on procedures and materials?
Also, what is the proper location to put the screws? Through the raised part or the valleys? I see both on my roof.
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Replies
Andy,
On the ribs-vs.-valleys question: In the old days, we were taught to install the fasteners on the ribs. Once high-quality screws were introduced, the advice changed, and we were taught to install the screws on the flat sections ("valleys").
If your screws are hitting the rafters, replace the short screws with new, longer screws (with new rubber washers).
Screwing into plywood isn't a great idea. Most roofers install metal roofing on purlins (1x4 or 2x4 strapping, installed parallel to the ridge), giving the roofing screws something better to bite into. I'm not sure what you can do now if you didn't install purlins.
Andy:
I have several metal roofs, and was surprised to read about all the backing out of screws you are experiencing. I guess I didn't realize until Martin clarified that the screws are only into plywood. I have used 2x4 purlins and screws of 2.5" without problems. If the roof is accessible from below, I suppose you could add 2x4 blocking for new screws; a bit of a tedious job but not difficult or expensive.
BTW, the ridges vs valley placement of screws is still pretty well divided. I checked this out pretty thoroughly recently prior to the installation of a garage roof. In the end I went with (mostly) ridges because the installation literature from the roofing manufacturer (Ideal Roofing) recommended ridges, esp in snow country. They did say valleys were also "acceptable" with 1.5" screws, but definitely preferred ridges. I put one screw in the valley at the lowest end of each sheet of roofing, over the soffit, in order to assure steel was tight to the purlin in between the ridges. I think the ridges are safer from a leakage standpoint.
I forgot to mention that with the valley option, the roofing folks still wanted a longer screw in the ridges that overlapped to the next sheet, presumably to hold those together as tightly as possible.
Andy:
https://www.greenbuildingadvisor.com/community/forum/energy-efficiency-and-durability/40122/metal-roof-fasteners-backing-out
Do the screws that have backed out, especially the stripped ones, show signs of corrosion on the threads? If so that may indicate you have moisture problems in the roof sheathing.
I would recommend using epoxy. This stuff can literally even secure a metal roof to the wood with out screws. It would be expensive though. For what your trying to do you won't need much. Be sure it is epoxy(should be a 1 to 1 two part epoxy) and not a cheaper alternative( 3 to 100parts mix is not epoxy) that may not be water proof. Knife grade epoxy would be best and is not to expensive.
Andy,
Have to recommend against epoxy or other attempts to "glue down" the roof. Even attempting to seal the laps between panels with a sealant should be done only with materials specifically made for the purpose. Metal roofs expand and contract a fair amount. Not as bad as vinyl siding, but enough to work the screws over time. Here in the southwest, where I am, the general advice for face screwed roofing is to plan on going up and tightening the screws every five years or so.
To avoid the maintenance hassle I chose to go with a clip style standing seam roof. The clips and screws in this system do not see the expansion wracking present in face screwed roofing. At least that is the theory. I will never know how the screws are doing until too late, I guess. The main point here is that the metal will expand and contract, which is something epoxy in any form I have encountered will not do.
Some manufacturers of ribbed materials have sealant tapes that are applied between overlapping ribs as the panels are set. I would have to assume that they are well aware of the stresses the panels undergo and the sealant is very flexible and resistant to hardening over time. You are likely stuck with whatever holes you have so the rib versus field placement decision has already been made for you. I can see that the rib placement might have value both for keeping the gasket up out of most snow melt issues and be slightly more forgiving and flexible in the face of expansion. Having a mix is a bit odd, but more important is heeding Malcolm's advice to check for moisture issues.
Yes this so very true but understanding a few things about epoxy as to even what is recommended as glue for sealing such things like this is key. Epoxy is and always will be if adhering wood and metal the strongest possible adhesive to use in any situation. Water proof yes. Permement? Well they do say so when usimg it to ancor bolts used in roofing commercially. Thing is that damage is done and it is probally the only fix that wont leak with out replacing roof or at least screws. Also prevents having to always have to upkeep now to try it on 1 and see if u decide to replace screws
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I've been having problems with the screws backing out on my metal roof. Unfortunately, the sheathing used was 1/2" OSB. I'm sure that was most of the problem. Two years ago the contractor who installed the roof came out and tightened the screws. A few screws were replaced with over-sized screws (5/16" hex head). To date none of those screws backed out. A few weeks ago I noticed two water stains on my vaulted ceiling. The culprit was one of the smaller, original screws. I went to the supplier and bought a couple of bags of the larger screws and now I'm replacing all of the screws. I also bought some Lexel caulk for added assurance. I put a dab of caulk on the threads and as it screws in the caulk mushrooms around the washer. I take my finger and smear some of the caulk onto the screw head. The Lexel caulk is pricey (about $10/tube) but it goes a long ways.