PV Racks for Sloped, Asphalt-Shingled Roofs: Page 5 of 5

Intermediate

Inside this Article

A rack system has the simple job of supporting the modules in a PV array.
Early rack solutions often included poor grounding techniques and inadequately protected roof penetrations.
Rail-based racks provide an easy way to level and align PV modules, as well as attaching module-level inverters and optimizers.
Rails run vertically for PV modules mounted in landscape orientation.
Top-down racking, like this system by RBI Solar, involves clamps that grip the module frames from above and supporting rails beneath. There are a variety of extruded rail configurations and clamping attachment systems.
Rail-free rack systems like this Quick Rack by Quick Mount PV use top clamps that integrate with mounting-foot locations.
Like others of its kind, this Roof Tech system allows subtle adjustment of horizontal and vertical alignment.
Material and shipping costs may be reduced by choosing rail-free systems. However, some systems may require more roof attachment points and more critical alignment.
Clamps at the module corners of this rail-less system by Quick Mount PV secure the module frames to the roof attachments. The gray rail is actually a trim strip, providing an aesthetic finish for the bottom of the array.
Clamps at the module corners of this rail-less system by Quick Mount PV secure the module frames to the roof attachments. The gray rail is actually a trim strip, providing an aesthetic finish for the bottom of the array.
Quick Mount PV’s online design tool.
A solid structural attachment directly to the roof rafters is ideal. However, attachment to blocking or even sheathing is possible with the proper product choices and engineering.
A typical flashing for a rack’s foot.
Post feet can be installed prior to roofing material, allowing reroofing without compromising the structure.
Various options for wire management can be integrated with racks, including clips, zip ties, and tucking wires into rail cavities. No matter what method is used, care must be taken to protect the wire’s insulation.

Wire management. Various third-party clips are available to help secure the PV module leads, home-run wiring, and MLPE cable assemblies. Some rack manufacturers have integrated wire management, which can help expedite the installation and protect the wiring. Good wire management helps ensure successful inspections, and prevents ground faults that are expensive to troubleshoot and can be a hazard to life and property.

Grounding. NEC Section 690.43(A) requires that any devices and systems used for mounting PV modules that are also used for bonding module frames be listed, labeled, and identified for such purposes. To meet this requirement, most rack systems include integrated grounding. The clamps and rails (and, sometimes, attachment hardware) are now listed to UL 2703 standard for “Rack Mounting Systems and Clamping Devices for Flat-Plate Photovoltaic Modules and Panels.” UL-listed hardware then connects the components together to form an electrical bond by cutting into the rack material and module frames. If UL 2703-listed racks are not used, then a ground wire needs to be connected to each module frame and, possibly, to each rack component in the system.

Fire classification. In 2012, the International Building Code stipulated that rooftop-mounted PV systems carry the same fire classification as the roof assembly. Previously, although PV modules had a fire class rating, the system, which includes the rack, did not. Based on this requirement, UL 1703 and 2703 standards include testing and fire classification for PV rack systems. If installing in a jurisdiction that enforces this IBC requirement, it is important to select a rack system that is code-compliant.

Choose Wisely

When selecting a rack system for a sloped-roof PV installation, there are many factors to consider and many rack manufacturers to choose from. The right rack system should be cost-effective and install quickly, but should also help decrease the soft costs associated with design, engineering, permit approval, and procurement. As the pressure to decrease BOS costs continues, installers are looking more closely at these ancillary benefits, selecting rack systems that support the PV modules and ease the installation process from start to finish.

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