Flashing for metal plates for roof-mounted solar system
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Our company makes a solar system roof mount that was designed to be flashed using a simple piece of sheet metal. The attached photos show the mounting plate before and after the flashing is installed. (The mount is a thick metal plate with screws in it that penetrate the roof shingles all the way into the rafters; the flashing tucks under the shingle above and protects these penetrations).
A roofer who was installing our system wanted to skip the metal flashing, and instead seal the mounting plate by using a self-adhering butyl membrane between the metal plate and the asphalt shingles, and then use roofing screws (i.e. screws with EDPM washers that are used for metal roofs) to make sure water can’t get into the screw holes.
We think this is a great idea and would love to recommend it to all of our customers. Installing the flashing is time-consuming, and it would save a lot of time and expense to skip it (a full installation could have 100 or more of these mounting plates and associated flashings).
Any opinions?
I would be most comfortable if we could find a tape or caulk that is warranted for 20 years+, and is rated for this application (sealing metal to composite shingle). Any pointers to products that anyone thinks would fit the bill?? Any other thoughts???
– Joe
Replies
Joe, could you take this further and explain with pictures......
the system you supply and install, assuming you take it further than just the roof mounts?
I'm no roofer, but I certainly know the importance of diverting water and protecting penetrations. The system you use now seems like it would work if no wind driven rain worked it's way up under the flashing. A pc of Vycor (like the roofer intends to use) under that plate would further aid in sealing the screws. A washered screw even better.
Without the flashing.......................beats me. Our weathervane was done similar to the roofers idea, to date I don't think water has made it under the shingles. No evidence under the roof sheeting. In 2020 or so when I need a new roof I could probably answer better on that application.
It's traditional to install the feet of rooftop antennas by placing a large dab of roofing cement under the bracket and then driving lag bolts through. This is crude but works pretty well (though I'm sure someone will speak up and say it failed for them).
No system's perfect. Your flashing scheme seems pretty good but is probably overkill in most cases.
Butyl membrane is a great product and tape is pretty common
This is typical of what we buy here in Florida:
http://www.dhcsupplies.com/store/p/1369-Protecto-Wrap-BT25-XL-Butyl-Hybrid-Peel-N-Stick-Membrane-Sealing-Tape.html
I'm not sure this is the best application for it Butyl tape ... I like your flashing detail but can see where it could be a real pain in the neck ... My concern with the butyl membrane / tape would be that you would squeeze it out due to the point load on the plate created by the screw / rafter connection. Once it's gone, there's no more seal around the screw below the plate, although the perimeter of the plate is fully embedded in the membrane, I still feel the water will leak down along the threads etc. etc.
Buytl tape is used by roofers to mend joints in the membrane or we use it to flash windows and doors ... in the case of the roof membrane there is no squeezing out load and in the window / door install, the load is uniformly applied to the edges of the frame and the screw passes through the "unsqueezed part" of the membrane.
Hate to shoot holes in your detail without offering a better solution and I'm not convinced the perimeter seal is not sufficient ... maybe this is just something to consider.
The link might be the most helpful part of my response.
Good Luck
Your argument is why I tend to prefer a blob of roofing cement.
Two things I think: 1. -
Two things I think:
1. - The gasketed screw is likely the wrong fastener for your application. It was meant to got through less material... and with that self drilling tip in conjunction with the metal type fine threads, you won't get the same pullout strength as conventional wood construction screws with Type 17 tips and coarse threads covering most of the screw. A washer/gasket on a panhead wood screw would fix that, but good luck getting crews to assemble this in the field each and every time. The other option would be to special order very long versions of the typical gasketed screw.
2. - Your flashing system is elegant and looks good. Yours is the system I am looking for (please post a link to your company!). I've already had to fix my roof because of some previous work that was done with quick and dirty "just good enough" methods... "hey, yer selling the house in 5 years right? You only need a 7 year roof!" I know times are tough and you are looking for ways to make your installations more efficient. Screw that. I'd sell your system as being the only one that recognized the importance of flashing on a roof system, and how others simply rely on a bead of goop to keep decades of water and sun away.