Attaching PV Modules to Tile & Metal Roofs

Intermediate

Inside this Article

A PV installation on tile roof.
Installing standoffs on a new roof, before tiling, is much easier than after the fact, as roofers can tile around mounting points, and flash as they go.
Standoffs like these by Unirac are secured by lags through sheathing and into rafters or purlin blocking. They are usually flashed at the deck level and again above tile level.
IronRidge XRS rail
Tile hooks like these by Quick Mount PV are designed to mount under a tile. The mount hooks between the courses of tiles.
Tile hooks like these by Quick Mount PV are designed to mount under a tile. The mount hooks between the courses of tiles.
Mounting tile hooks requires removing tiles. They are reinstalled after deck flashings, and prior to installing rails and PV modules.
A tile replacement mount like this one by SnapNrack uses flashings that mimic the shape of the tile it’s replacing.
Ecolibrium Solar’s mount is a cross between a tile hook and a tile replacement mount that uses a tile-matching flashing.
Ecolibrium Solar’s mount is a cross between a tile hook and a tile replacement mount that uses a tile-matching flashing.
Like others, these Quick Mount PV tile replacement mounts are available for flat tile, W-tile, or S-tile, and in various base, standoff, or S-hook versions to match the needs of each installation.
Like others, these Quick Mount PV tile replacement mounts are available for flat tile, W-tile, or S-tile, and in various base, standoff, or S-hook versions to match the needs of each installation.
Like others, these Quick Mount PV tile replacement mounts are available for flat tile, W-tile, or S-tile, and in various base, standoff, or S-hook versions to match the needs of each installation.
The advantage of standing-seam metal is that the standoff hardware attaches to the roof without any penetrations.
EcoFasten Solar’s standing-seam clamps also function as rail-less racking by including a base to support module frames and a top clamp.
EcoFasten Solar’s standing-seam clamps also function as rail-less racking by including a base to support module frames and a top clamp.
S-5! is a longtime provider of metal roof attachment products, producing clamps to match several standing-seam profiles.
Orion Solar Racking seam clamps
Watertight hanger bolts can penetrate metal roofs into the underlying structure to secure standoffs.
Schletter manufactures both fixed (shown) and adjustable trapezoidal attachments.
EcoFasten Solar’s Corruslide adjustable attachment is appropriate for trapezoidal and corrugated roofing.
S-5! fixed and adjustable trapezoidal-profile mounting products.
Roof Tech’s RT-[E] mount attaches through the flat area of roofing to the sheathing below.
Mounting Systems’ Tau+ product mounts to the top of the trapezoid.
SunModo’s self-sealing standoff can be used on metal roofs without sheathing but must penetrate into the roof support structure.
S-5!’s corrugated roof mount attaches through the valleys.
Preformed Line Products’ simple mount penetrates through the ridge, but bears weight in the valleys.

Over the past decade, solar rack design and manufacturing solutions have evolved to include tile and metal roof options that are attractive, well-designed, and long-lasting.

Four Things to Look For

As a solar installer, I evaluate four things when selecting an attachment method and rack system: strength, durability, aesthetics, and ease of installation.

A rack system has to be strong enough to safely support the PV modules and other equipment, such as microinverters or DC converters, and remain secure and in place under the stresses of wind or snow loads. Racks can be either rail-based or rail-less systems (see “PV Racks for Sloped, Asphalt-Shingled Roofs” in HP181 for more information).

A rack system should last at least as long as the roof—preferably much longer. For some metal roofs, this could be more than 50 years. A quality tile roof may require major refurbishment every 25 years, but will last for decades.

Both consumers and PV installers appreciate an aesthetic rack solution. With the lower cost of today’s solar-electric components, installers can design systems that perform well and look great. A rack and mounts that are easy to install can also save money by speeding up the installation.

Evaluating the Roof

When you install a rooftop PV system, you’re asking more from your roof, since it will be supporting the additional weight of the rack and mounts, PV modules, wiring, electrical conduit, and wind (and, possibly, snow) loads. It must also support the weight of technicians and tools during installation and maintenance.

Before you add a PV system, assess (or hire a pro to assess) the condition of your roof from top to bottom. If the roof needs to be replaced, do so before installing a PV system. Otherwise, you’ll have to pay twice for the system’s installation (and also once for the system to be removed). If roof work is required, make sure your roofer and solar installer each understand their parts in the process and are communicating. You’ll also want to know what warranties apply to your roof after your PV system is installed.

Tile Roof Options

Most modern pitched roofs have commonalities. There are structural members, usually trusses or rafters, which are attached to the walls and support the weight of the whole roofing system (and the PV system). Decking—either solid boards or plywood—is secured to the top of the structural members.

The topmost roofing layer is the roof’s first line of protection from the weather. Tiles are made of concrete, clay, or a composite material, and formed into shapes that overlap each other. Concrete tiles are often referred to by the end shape they make when viewed from the ground: flat tiles, W-tiles, or S-tiles.

Starting at the bottom of the roof, these tiles are placed in rows and fastened to battens—thin strips of metal or wood that run horizontally across the roof to keep each row of tiles from sliding down the roof.

Between the roof decking and the battens is the tile roof’s underlayment, which protects your home from moisture intrusion. Preserving this water-resistant layer is vital, and that means paying close attention to flashing and sealing around all penetrations, including plumbing and attic vents, and of course, any PV system attachments.

Tiles overlap the course below enabling water to flow from the top of one tile onto the next tile. It’s still possible for some water to make it through to the also-protective underlayment, so it’s important to flash any attachments that protrude through the tile layer to direct water onto the surface of the roof, not down to the underlayment.

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Comments (5)

sebastian koch_2's picture

A very nice article! I have had solar panels on a flat roof that needed to be re-roofed. I did my best to coordinate with the solar installer and roofer. The solar installer recommended to remove the entire mounting system so that the roofer could do the roof. I wanted a slope on the flat roof, to avoid water pooling, and the roofer put a tapered roofing system which is about 4 inches thick at its widest part. The solar installer now cannot place the mounting system back on, because the L brackets, which need to be directly attached to the roofing deck, would crush the tapered roofing system. I am now being told that individual pitch pans would have to be created to optimally attach the panels and waterproof the roof. There are 36 attachments for the mounts and this is obviously labor intensive and expensive. Is there an alternate solution? Thanks for any comments.

Michael Welch's picture
Yikes, that's a bummer. Did the roofer have permits to alter the roof pitch? Did an engineer sign off on the new roof for wind and/or snow loads?

Seems to me that if the roofer did the job correctly, the new roof joists would be strong enough to mount the PV modules back on. I don't know the details, but maybe you could check on the above and maybe enlist an engineer to help.

Finally, check into using a ballasted PV system rather than L brackets. But, the new roof has to be strong enough to handle the added weight.
rfwatts@gmail.com's picture

It is worthy of note that you absolutely must test any of the metal roof clamps on a sample of your metal roof. I had a new metal roof on my house and decided to use clamps held in place by set screws. As the installer was setting the last clamp in place, he removed it and examined the roof metal 'just in case'. Unfortunately, there were cracks in the metal from the set screws. In fact, there were cracks under every set screw. We had to have the entire roof replaced, and use a different mounting method for the rails (posts with screws through the roof, lots of sealant). Metal roofing quality is different from different manufacturers, and you need to be sure your clamp vendor guarantees no problems with your particular roof material vendor well ahead of time. Our clamp vendor replaced the roof at their cost and made us whole, and of course immediately removed our metal roof vendor from their approved list. I strongly recommend you test a sample of the roofing with whatever clamp you have decided to use before you have an entire roof full of cracks.

Louis Woofenden's picture

A useful cautionary tale! I'd agree, it's always a good practice to test before putting clamps on the whole roof. Had the clamp vendor tested their clamps with that particular roof profile before?

rfwatts@gmail.com's picture

The vendor assumed that the clamp/roof connection would be OK, since they had tested with very similar roofing before. They were shocked to find how badly the metal cracked. Nowadays they are very specific about which roof products they will work with. So no, they had not tested on this particular material before. I would be very, very cautious about using a clamp with set screws without testing one or more samples first. Forewarned is forearmed, as they say.

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