You spent a lot of money on your tile roof. And now you want solar panels. Obviously, you want to make sure that your new roof will not leak.
The process for installing solar panels on your tile roof sounds scary until you understand some of the realities of how your roof is installed and how far solar mounting products have come.
We always hear about “penetrations.” There are two kinds of penetrations to a roof.
First, we have traditional penetrations like plumbing vents and air circulation vents. Solar panel installations typically have one of these penetrations per roof surface to get electrical conduit into the attic. This single penetration is the most important because it is a larger hole that must be sealed and “flashed” to prevent water entry. Flashings are metallic, composite, or plastic parts that shed water away from penetrations. There are many flashings available for this purpose. When done correctly, these penetrations are as good as, and often better than, all of your existing plumbing and ventilation penetrations. Since the quantity is low, the risk is very low.
Second, there are the more numerous “penetrations” from fasteners (screws, bolts, etc). These do penetrate the waterproofing membrane (underlayment) and you may have dozens or even hundreds of fasteners used in a typical installation. That sounds scary, but actually, it’s almost impossible for these penetrations to leak when done properly. More importantly, you might not realize something important… you have thousands of screw penetrations through your roof already. Each tile is likely fastened to the roof deck with one or two screws.
What makes this even more consequential is how tiles are secured versus how solar mounts are secured. Tiles use a very small diameter screw, not stainless steel, and fastened only to the wood deck, not to structural trusses. There is no sealant added. Movement of tiles via expansion and contraction, wind, and other physical means causes screws to be under stress over the years. The underlayment does a good job of sealing around the screw, but the screw can move slightly and the tile can rub against the waterproofing membrane. This is very different from how solar panel mounts penetrate your waterproofing membrane.
Solar mounts use large diameter fasteners, typically 1/4 inch or 5/16 inch, fastened into structural trusses. This sandwiches the roof decking between the solar mount and the truss. A high-quality sealant is used in the pilot hole that is drilled first. More sealant is used around the penetration(s). Then a base flashing is installed over the mount with roofing cement sealing the flashing to the waterproofing membrane. The base mount cannot move since it is tightly attached to the membrane. Then a top flashing is installed over the tile, or a top flashing replaces the tile altogether. This provides a rock-solid waterproofing system that is impenetrable to water. It is much more reliable than the tile screw attachments.
If your contractor uses any system other than what is described above, they are doing you a disservice. The leader in the industry is Quick Mount PV. Their Tile Replacement Mount, Universal Tile Mount, and Tile Hooks all use this multi-faceted waterproofing system. When expertly installed, this system is bulletproof.
Note that there are circumstances where deck-mounting is acceptable when approved by a professional engineer. However, tile roof deck mounts almost always use multiple fasteners per mount, making them much less susceptible to lateral movement than tile screws. They are also flashed as described above when done properly.
The bottom line is that you don’t need to be afraid of penetrations when you hire a qualified contractor who uses the proper materials. You already have thousands of penetrations to your roof. The dozens of solar mount penetrations a good solar contractor adds will not significantly increase the risk of leaks. The materials available to contractors today are light years ahead of the old solar mounts from decades ago. The industry is mature and sophisticated in its approach to roof protection.
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