Each type of roof has its own characteristics that contractors must consider when installing solar panels. Metal roofs come in a wide variety of profiles and materials and require specialized fastenings, but installing solar panels on these specialized roofs is easy.
Metal roofs are a common roofing option for commercial buildings with slightly sloping tops, and are also becoming increasingly popular in the residential market. Construction industry analyst Dodge Construction Network reported that U.S. residential metal roof adoption has increased from 12% in 2019 to 17% in 2021.
A metal roof may be noisier during hail storms, but its durability allows it to last up to 70 years. At the same time, asphalt tile roofs have a shorter service life (15-30 years) than solar panels (25+ years).
“Metal roofs are the only roofs that last longer than solar. You can install solar on any other type of roof (TPO, PVC, EPDM) and if the roof is new when the solar is installed, it will probably last 15 or 20 years,” says CEO and Founder Rob Haddock! Manufacturer of metal roofing accessories. “You have to remove the solar array to replace the roof, which only hurts the projected financial performance of solar.”
Installing a metal roof is more expensive than installing a composite shingle roof, but it makes more financial sense for the building in the long run. There are three types of metal roofing: corrugated steel, straight-seam steel and stone-coated steel:
Each roof type requires different solar panel installation methods. Installing solar panels on a corrugated roof is most similar to installing on composite shingles, as it still requires mounting through openings. On corrugated roofs, insert transoms into the sides of a trapezoidal or raised portion of the roof, or attach fasteners directly to the building structure.
The design of the solar pillars of the corrugated roof follows its contours. S-5! Manufactures a range of corrugated roof accessories that use sealed fasteners to waterproof each roof penetration.
Penetrations are rarely required for standing seam roofs. Solar brackets are attached to the top of the seams using corner fasteners that cut into the surface of a vertical metal plane, creating recesses that hold the bracket in place. These raised seams also serve as structural guides, which are often found in solar projects with pitched roofs.
“Basically, there are rails on the roof that you can grab, clamp and install,” says Mark Gies, Director of Product Management for S-5! “You don’t need as much equipment because it’s an integral part of the roof.”
Stone-clad steel roofs are similar to clay tiles not only in shape, but also in the way solar panels are installed. On a tile roof, the installer must remove a portion of the shingles or cut the shingles to get to the underlying layer and attach a hook to the roof surface that protrudes from the gap between the shingles.
“They typically sand or chip the tile material so it can sit on top of another tile as intended and the hook can go through it,” said Mike Wiener, marketing manager for solar panel manufacturer QuickBOLT. “With stone-coated steel, you really don’t have to worry about it because it’s metallic and overlaps. By design, there should be some room for maneuver between them.”
Using stone-coated steel, installers can bend and lift metal shingles without removing or damaging them, and install a hook that extends beyond the metal shingles. QuickBOLT has recently developed roof hooks specifically designed for stone-faced steel roofs. The hooks are shaped to span the wood strips to which each row of stone-faced steel roofing is attached.
Metal roofs are primarily made of steel, aluminum, or copper. On a chemical level, some metals are incompatible when in contact with each other, causing what are called electrochemical reactions that promote corrosion or oxidation. For example, mixing steel or copper with aluminum can cause an electrochemical reaction. Luckily, steel roofs are airtight, so installers can use aluminum brackets, and there are copper-compatible brass brackets on the market.
“Aluminum pits, rusts and disappears,” Gies said. “When you use uncoated steel, only the environment rusts. However, you can use pure aluminum because aluminum protects itself through an anodized layer.”
Wiring in a solar metal roof project follows the same principles as wiring on other types of roofs. However, Gies says it’s more important to prevent wires from coming into contact with the metal roof.
The wiring steps for track-based systems are the same as for other types of roofs, and installers can use the tracks to clamp wires or serve as conduits for running wires. For trackless projects on standing seam roofs, the installer must attach the cable to the module frame. Giese recommends installing ropes and cutting wires before the solar modules reach the roof.
“When you’re building a trackless structure on a metal roof, more attention needs to be paid to preparing and designing jumping areas,” he says. “It’s important to prepare the modules in advance – have everything cut out and set aside so nothing is hanging. It’s good practice anyway because installation is easier when you’re on the roof too much.”
The same function is performed by the water lines running along the metal roof. If the wires are routed internally, there is a single opening at the top of the roof with a junction box for running the wires to the designated load point indoors. Alternatively, if the inverter is installed on an external wall of the building, the wires can be routed there.
Even though metal is a conductive material, grounding a metal roof solar project is the same as any other type of grounding on the market.
“The roof is over the top,” Gies said. “Whether you’re on the pavement or somewhere else, you’ll still have to connect and ground the system as usual. Just do it the same way and don’t think about the fact that you’re on a metal roof.”
For homeowners, the appeal of metal roofing lies in the material’s ability to withstand harsh environmental conditions and its durability. Solar installers’ construction projects on these roofs have some material advantages over composite shingles and ceramic tiles, but may face inherent risks.
Composite shingles and even stone-coated steel particles make these roofs easier to walk on and grip on. Corrugated and standing seam roofs are smoother and become slippery when it rains or snows. As the roof slope becomes steeper, the risk of slipping increases. When working on these special roofs, proper roof fall protection and anchorage systems must be used.
Metal is also an inherently heavier material than composite shingles, especially in commercial scenarios with large roof spans where the building cannot always support the additional weight above.
“That’s part of the problem because sometimes these steel buildings aren’t designed to hold a lot of weight,” said Alex Dieter, senior sales and marketing engineer for SunGreen Systems, a commercial solar contractor in Pasadena, California. “So depending on when it was built or what it was built for, it finds the easiest solution or how we can distribute it throughout the building.”
Despite these potential problems, installers will undoubtedly encounter more solar projects with metal roofs as more people choose this material for its strength and durability. Given its unique features, contractors can hone their installation techniques like steel.
Billy Ludt is a senior editor at Solar Power World and currently covers installation, installation and business topics.
“Aluminum pits, rusts and disappears,” Gies said. “When you use uncoated steel, only the environment rusts. However, you can use pure aluminum because aluminum protects itself through an anodized layer.”
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Post time: Feb-24-2024