Each type of roof has its own specifics that contractors must consider when installing a solar project. Metal roofs come in a variety of profiles and material compositions that require special brackets to accommodate them, but installing solar panels on these specialized roofs doesn't have to be difficult.
A solar company attaches modules to a metal standing seam roof. S-5!
Metal roofing is a common covering choice for commercial buildings with a gently pitched roof, and it's also gaining popularity in the residential market. The Dodge Construction Network, a construction industry analyst, released a report claiming that residential metal roofing adoption in the United States increased from 12% in 2019 to 17% in 2021.
Metal roofs may be a little noisier in a hailstorm, but their durability contributes to a 70-year lifespan. Meanwhile, asphalt shingle roofs have an even shorter lifespan (15-30 years) than solar panels (25+ years).
“The metal roof is the only roof that lasts longer than the solar. You install solar on every other type of roof - TPO, PVC, EPDM - when the roof is new, when you install the solar it lasts maybe 15 or 20 years,” said Rob Haddock, CEO and founder of S-5!, a manufacturer of metal roof fasteners. "You have to dismantle the solar to replace the roof and that destroys the financial pro forma of the solar."
Installing metal is more expensive than a composite shingle roof, but could make more long-term economic sense for a building. The three types of metal roofing are corrugated, standing seam and stone faced
Corrugated iron roofs consist of long sheets of metal covering the length of a roof surface and have built-in corrugations, such as rounded corrugations or trapezoids. The sheets are attached to the surface of the roof, meaning they use visible fasteners to secure to a building.
Standing seam roofs are also manufactured in sheet metal, but are mostly flat except for interlocking channels attached to either side of the roof panel. These channels or ribs have hidden fasteners that secure each roof panel in turn, leaving a protruding seam. Stone coated steel roofing resembles clay tiles or shingles more closely than corrugated iron or standing seam roofing. Smaller steel sheets are shaped into bricks and coated with stone granules.
Fasten to metal
Each of these roof types requires different mounting techniques for solar projects. Fastening solar panels to corrugated iron roofs is most similar to installing on composite shingles, as securing by penetrations is still necessary. On a corrugated iron roof, a screw is driven through the sides of a trapezoid or raised portion of the roof, or the bracket is attached directly to the building structure.
Solar mounts for corrugated iron roofs are designed to follow their contours. S-5! manufactures a range of corrugated iron roofing fasteners that use bolts with gaskets to make any roof penetration watertight.
Penetrations are rarely necessary for a standing seam roof. Solar mounts are attached with slanted screws that penetrate the surface of the vertical metal plane to create indentations that hold a mount in place. These raised seams can also act as structural rails, often seen in pitched roof solar projects.
"You basically have rails on the roof that you just grab, grip and install," said Mark Gies, director of product management at S-5! "You don't need that much hardware because the hardware is sort of an integral part of the roof."
Stone coated steel roofing resembles clay tiles not only in shape but also in the way solar is installed on it. On a tile roof, installers must either remove part of the tile or cut through the tile to reach the underlay and attach a hook to the roof surface that protrudes through the gap between the tiles.
"Usually they grind or gouge out the brick material so it can rest on the other brick like it's supposed to and the hook can get through," said Mike Wiener, marketing manager at QuickBOLT, a manufacturer of solar fasteners. “You don't really have to worry about that with stone coated steel because it's metal and it overlaps. It's designed to have some clearance between the bricks."
With stone-coated steel, installers can bend and lift this metal shingle without removing or breaking it, and similarly install a hook that extends beyond the shingle. QuickBOLT has recently developed roof hooks suitable for stone coated steel roofs. The hook is shaped to fit around the wooden batten to which each row of stone faced steel roofing is attached.
Chemical and electrical considerations
Metal roofs are mainly made of steel, aluminum or copper. On a chemical level, there are metals that are incompatible when they touch, leading to a so-called galvanic reaction that can cause corrosion or oxidation. For example, crossing steel or copper with aluminum can cause a galvanic reaction. Fortunately, steel roofs are sealed so installers can use aluminum brackets, while there are brass brackets on the market that are compatible with copper.
"Aluminum will pock up, rust away and disappear," Gies said. “Uncoated steel will rust from the environment alone. Whereas you can have bare aluminum because aluminum protects itself with a layer of anodizing.”
Running cables on a metal roof solar project follows much of the same principles as running cables on other roof types. However, it's more important to keep the cables away from the metal roof, Gies said.
Wiring a track-based system follows the same steps as other roof types, although installers can use the track to secure the cables or as a conduit for cable routing. For railless projects on standing seam roofs, installers need to attach the strands to the module frames. Gies recommends determining strand routes and securing cables before the solar panels even reach the roof.
"There's more emphasis on preparation and design of the strand jump locations when you're doing trackless on a metal roof," he said. “It's important to prepare the module in advance - that everything is secured and out of the way and nothing is hanging. That’s good practice anyway, because then it’s so much easier to install on the roof.”
Laying power lines works the same way on metal roofs as on other roofs. If the wiring is routed internally, there is a single penetration at the top of the roof with a junction box that carries the wiring to the intended load point inside. Or if inverters are mounted on the outside wall of the building, the cables can be routed there instead.
Despite the fact that metal is a conductive material, grounding a solar project to a metal roof is the same as any other style on the market.
"The roof is sort of out of the frame," Gies said. "You still have to connect and ground the system like you normally would, whether you're on tarmac or whatever. Just do it the same way and don't think about it, you're on a metal roof."
For building owners, the appeal of a metal roof is a long service life with a material that can withstand the elements. Solar installers building projects on these roofs have some material advantages over composite shingles and tiles, but may also face inherent risks.
The granules in composite shingles and even in stone faced steel make it easy to walk and grab onto these roofs. Corrugated iron and standing seam roofs are smoother and can be slippery in rain or snow. The risk of slipping increases the steeper the roof becomes. Proper fall protection and anchoring systems should be used when working on these particular roofs.
Metal is also an inherently heavier material than composite shingle and, especially in commercial scenarios with longer roof spans, buildings cannot always support additional weight at the top.
"Part of the challenge is that sometimes these steel buildings aren't built to support a lot of weight at the top," said Alex Deeter, senior sales and marketing engineer at SunGreen Systems, a commercial solar contractor based in Pasadena, California. "So, depending on when it was built or what purpose it was built for, it's a matter of figuring out what the lightest solution is or how we can distribute it across the building."
Despite these potential challenges, installers will no doubt encounter more solar projects on metal roofs as more people choose this material for its durability and lifespan. With his special considerations in mind, contractors can refine their installation practices like sharpened steel.