The Right Fit

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

Equipment innovations and new National Electrical Code criteria have led to wider choices in PV mounting systems. Here’s a guide to help determine what mounting system is right for your modules. 

Roof installations are often the most cost-effective option for residential PV applications and therefore typically the first area evaluated on a property, and that’s the focus of this article. However, not all rooftops are appropriate for solar—there may be roof obstacles, such as vents and chimneys, which create too much shading; the underlying structure may not be sound; or the roof’s location and/or orientation may not be suitable. (Look for upcoming articles on ground-, pole-, and awning-mounting systems in future issues of Home Power.)

Mechanical Evaluation

The mounting product must be able to meet the location’s wind and snow loads. Most building jurisdictions around the country have adopted some version of the International Building Code (IBC), which provides guidelines and methodology for evaluating structures for their ability to withstand expected snow loads as well as the forces from wind and seismic events. Manufacturers of PV mounting equipment often supply an engineering analysis and calculations showing that their product meets certain load requirements. Within this engineering analysis, the manufacturer often supplies tables that summarize the engineering analysis into helpful reference charts. System installations with parameters outside the assumptions made in the report require additional evaluation to determine appropriate design, a service that many rack manufacturers offer.  

Load ratings. The first step in evaluating rack options is to collect basic site information necessary to utilize the manufacturer’s load-rating charts. Site details include: building (or array) height from grade; wind exposure category; basic wind speed; snow load; and roof pitch. With this information, the rail span distance can be determined from the manufacturer’s load charts. Wind exposure classifies surrounding terrain into categories depending on the amount of open space around the building. Most mounting products are rated to at least a category C exposure level, which applies to rural locations with lots of open topography around the building area. Basic (or design) wind speed is defined as the greatest 3-second burst of wind speed recorded for the area. This can be obtained by contacting the local building department. Snow load ratings are also available from local building departments. However, in mountainous regions, also take into account snow load advice from locals, since snowfall can vary widely depending on elevation and microclimate. Roof pitch defines the tilt for the PV array and can be measured with an inclinometer. 

Most rack manufacturers provide professional engineered structural guidelines for the installation of their product, indicating the product has been evaluated to IBC requirements. Pre-approved product engineering analysis reports, specific to a state or region, provide assurance that a particular mounting product and installation parameters have been reviewed by a third party to meet site-specific load conditions. It can decrease the amount of time and cost associated with this portion of the permitting process.  

Local jurisdictions may enforce additional codes. For instance, the 2012 International Fire Code (IFC) has new requirements for setbacks and access pathways that may limit the available roof area for installing PV modules. 

Installation Details

Once the necessary structural and engineering criteria have been met, the next step is to analyze the mounting product for ease of installation.

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Comments (2)

Milton P Nogueira's picture

HI Jeff,
Although you have listed a few companies, I am sorry I haven't been able to reach out to you before...
I write to introduce Roof Tech which brings a 40+ yr. experience on roofing and mounting structures from Japan and as you know Japan being a country of the elements, you can certainly trust our engineering.
I 'll be happy to share with you the documentation we have for structural and seal ability.
We have addressed the issues of thermal contraction and expansion of the conventional racking with our rail-less solution, while preserving the roof integrity with a full water proof solution that performs to the test of time.
If you visit our www.roof-tech.us you will find our PE reports based on the IRC and IBC 2006, 2009 and 2012.
I am also available to answer any of your questions.
I can be reached at milton.n@roof-tech.us

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.

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