The Right Fit: Page 2 of 4

Hardware Solutions for PV Systems on Pitched Roofs
Intermediate

Inside this Article

Hardware Solutions for PV Systems on Pitched Roofs
What you need to know to choose a PV roof-mounting system that is appropriate for your home.
Flashed mount
This flashed mount uses a hanger bolt to screw into the roof structure and attach to the rail.
Hardware for standing-seam metal roofs
Mount hardware for standing-seam metal roofs relies on the roofing panels that are secured to the underlying roof structure.
The Quick Hook for tile roofs
Quick Mount PV offers flashing solutions for many roof types. Shown: The Quick Hook for tile roofs is designed for flat and S-shaped tiles, and requires roofing battens.
The QBase and Shake & Slate mount
The QBase and Shake & Slate mount is made for wood shake and slate roofs, and used with 18- by 18-inch flashing.
Captive hardware
Well-designed captive hardware allows placement anywhere along the length of the rail.
Mounting system
This mounting system provides both vertical and horizontal rail adjustment, using one bolt to secure the rail and clamp the rail hardware to the post.
An end-clamp.
An end-clamp.
A universal midclamp.
A universal midclamp.
Railless mounting systems
Railless mounting systems incorporate the mounting and grounding means into the module frame and hardware.
Module ground wire
A neatly installed module ground wire. Care must be taken to ensure the copper doesn’t touch the rails, module frames, or other nonstainless hardware.
Ground straps
Ground straps help ensure grounding is continuous through rail splices.
Wire management built into the rails
Wire management built into the rails makes for a neater, quicker installation. The plastic clip helps keep the cabling confined within the rail.
Microinverter
Like PV modules, microinverters or module-level MPPTs require grounding and wire management.
Online configuration tools
Some rack manufacturers offer free online configuration tools for designing a mount system.
Online configuration tools
Some rack manufacturers offer free online configuration tools for designing a mount system.
Hardware Solutions for PV Systems on Pitched Roofs
Flashed mount
Hardware for standing-seam metal roofs
The Quick Hook for tile roofs
The QBase and Shake & Slate mount
Captive hardware
Mounting system
An end-clamp.
A universal midclamp.
Railless mounting systems
Module ground wire
Ground straps
Wire management built into the rails
Microinverter
Online configuration tools
Online configuration tools

Roof-mount rail span. The load design calculations determine rail span—the distance between attachment points required for each rail. This distance also dictates the location and number of roof attachment points—a key aspect of array layout.  Stronger rail systems can allow greater spans between the attachment points, reducing the number of roof penetrations as well as the installation time. Fewer attachments also translate into material and cost savings. Typical rail spans can range from 4 to 10 feet, although this will vary by location. Installations with heavy snow or wind loads often have a rail span closer to 4 feet to account for increased force on each attachment point. While roof-mounted systems installed in milder climates may be able to span 6 feet or more between attachment points. With basic information regarding local conditions including roof pitch, building height, wind speed, exposure category, and snow load, the rail span can be determined by utilizing the tables and charts provided by the manufacturer.  

Using the example rail span table, we see that the maximum rail span between attachment points is 92 inches, given the following conditions:

  • Basic wind speed: 90 mph
  • Snow load: 10 psf 

A snow load of 20 psf would require reducing the maximum rail span to 80 inches.  

Attachment details will depend greatly on the roof material and the specific mounting product. There are four basic residential roof surfaces: asphalt shingles, metal roofing, tile, and slate

Asphalt roof installations require attachment to the building rafters or trusses via using lag screws or hanger bolts (a lag-type screw with an end threaded to receive a nut instead of having a head). In areas with heavy snow loads, using two hanger bolts per attachment may be necessary. The hanger runs up through a mounting base and attaches to the L-foot or standoff post. This entire assembly needs to be properly flashed before attaching mounting rails. Attachment hardware and flashing options may be offered as accessories or these products can be purchased from manufacturers that specialize in flashing components. Quick Mount PV products cover a wide variety of roofing applications including a couple of options for asphalt shingle roofs. Ejot is another option for attachment and flashing products.  

Metal roofing comes in three different types: standing seam, corrugated, and exposed metal fastener roofs (aka classic rib profile or Pro-Panel). Mounting a PV rail system to a standing-seam roof means no roof penetrations—special clamps are attached to the “rib” profile of the standing seam area where two roofing pans are connected. The clamp provides an attachment point for connecting rails or directly mounting modules. S-5! offers a variety of products to match various standing-seam profiles as well as an option for rail-free mounting. EcoFasten Solar offers standing-seam clamp products and SnapNrack also has an option for its roof-mount product.  

Exposed metal fastener and corrugated metal roof panels require specialized solutions. Many products require attachment to metal purlins below the roofing surface. Renusol offers a product for this roof type that enables attachment directly to the rib profile via roofing screws.  Hanger-bolt attachment systems may not be appropriate for these metal roof types due to challenges and inconsistencies between the layout of rafter and rib profiles.  

For tile roofs, standoffs, which may be tile roof hooks or posts threaded onto a hanger bolt, must be tall enough to clear the profile of the tile. Tile roof hooks can often be installed without drilling or notching tile pieces, simplifying the installation process. However, with this option, verify the deflection that may occur from snow and wind loading at the site. Excessive deflection can cause clearance issues underneath the array and may be a concern for module warranty regarding permissible deflection.   

Comments (1)

hans harder's picture

Since athletics are being discussed in this article, I think it would be worth mentioning a few points:
Mixing portrait and landscape on a roof face, may help you squeeze a couple more panels up there but it really isn't a very attractive option and should be avoided.
Silver or "clear" module frames should be reserved for commercial jobs. At least customers should be made aware that there is an option between black and clear, so they aren't disappointed for the next 20 years looking at a system that already looks dated the day its installed. Most customers typically don't mind paying a fraction more for a black on black module (black frame and black back sheet). They just need to be made aware that there is an option.

J- boxes on the roof should be hidden under the array whenever possible and if there is any way to avoid running visible surface mounted pipes across the roof it should be done. Amazingly some installers even think its acceptable to run a pipe around the outside of the roof eve and bring it back to the wall to continue down the side of the house.
When a house has an open attic space, consider relocating a plumbing vent to another part of the roof if its going to break up an otherwise clean array on the front of a house. It really isn't that much extra work.
Orphan panels, or just single panels put wherever they can fit looks bad and is extra work and materials for installers.
Feet outside the array- (classic rookie mistake) the rails allow for some overhang on the ends so it is almost always possible the keep those roof penetrations under the array and not have feet and rail continuing past the last module.
I know there are customers who say they don't care how the system looks on their roof, but you are doing the whole industry a disservice by installing ugly arrays. Typically it doesn't take that much more work to take some pride in your installation. As a company set design standards for your sales people to shoot for.
Sure you might be able to squeeze one more panel over there on that south part of some dormer roof but is it even worth it? The labor involved in mounting and running wires to these fragmented arrays often makes it worth adding a couple more modules on an off orientation roof pitch. Modules are relatively really inexpensive now days and it might just be more worth while to add a couple more on that east roof face array than an extra half day of labor for two guys.

Please think about some of these points next time you are signing papers in a customers beautiful kitchen.

Show or Hide All Comments

Advertisement

X