PV Racks for Sloped, Asphalt-Shingled Roofs: Page 2 of 5


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.

The lay-in lug method eventually evolved into the use of a washer electrical equipment bond (WEEB) to bond the modules to the rack system. At the time, this was revolutionary, as it dramatically decreased the installation time. However, with this method came unique issues, as properly locating the WEEB between module frames can be difficult. Plus, the sharp points on the washer that pierce the anodized module frame to create the bond wear out very quickly if the module needs to be unclamped and shifted during installation or maintenance. And, since the WEEB is hidden under the module frame, it is difficult for the installer or the inspector to verify that a reliable bond has been formed between the module and the rail. 

Modern Racks

In most systems, extruded aluminum rails support each row of modules, and clamps hold the PV modules in place. A flashed post, L-foot, or metal block elevates the rails; and a lag screw secures the system to the framing below. The main change is that roof racks have been simplified and are now available as complete systems with all components and hardware included, which can be adapted to most roofs.

Two rack system types dominate for parallel-mounted, sloped-roof applications: rail-based and rail-free. Whether rail-based or rail-free, each has benefits and disadvantages. Variations exist between manufacturers, and quality is a key consideration for selecting a rack system for a sloped roof. Some of the hallmarks of a quality product include manufacturer longevity and their support during the design, permitting, and installation phases of the project. Post-installation support and the rack’s accompanying warranty are also important considerations.


Rail-based racks have been the mainstay of the industry for decades. This system is simple, reliable, and can be adapted to most roof pitches and roof types. In most systems, there are two rails per module row; top-down (installable from above) clamps between modules hold them in place. These rails make it easy to connect to the roof surface with various attachment methods like L-feet, tile-hooks, or standing-seam clamps, and integrate easily into the waterproofing system with flashings from the rail manufacturer or a third-party supplier.

Another benefit of a rail-based system is they do not need to be precisely placed in relation to the module frame. This is helpful because courses of shingles are almost never in a straight line, and flashings are limited to where they can be installed and still maintain water-tightness. As long as the rail supports the module within its manufacturer-specified clamping zone, then the rail can be placed where it’s most convenient. Installing the rail to closely follow the shingle line will help ensure a leak-free penetration.

Rail systems also provide a mounting place for module-level power electronics (MLPEs). Microinverters and DC converters are capturing an increasing share of the market. These are typically installed one per module, but with some systems two or more modules are connected to a single rack-mounted microinverter or DC converter. Rails also help conceal and secure MLPE wiring.

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