Pitched Roof Racking SolarPro Magazine

Pitched Roof Racking SolarPro Magazine

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The best way to promote your solar business is through a happy, loyal customer’s word of mouth. Not much will damage your reputation and your customer’s confidence more than a roof that leaks.

Building codes require securing PV racking systems adequately to a pitched roof ’s structural members. Unless the roofing material is standing seam metal, where nonpenetrating S5! clamps are typically used, multiple lag screws or through-bolts have to penetrate the roofing material and sheathing in order to secure the racking system. Each of the associated holes is a potential entry point for water into the structure for the entire life of the system.

The liability involved in making holes in someone’s roof is considerable. Construction defect litigation is on the rise, especially in California. At the same time more PV is being installed on new construction and integrated onto ever for solar contractors. The good news is that by using common sense and appropriate materials and techniques, you can minimize your liability and save time and money by eliminating callbacks.


The first step in leak-free roof mounting is locating the rafters without making any unnecessary penetrations in the roofing. Finding rafters or other structural members is often the most tedious part of a PV installation. Ultrasonic stud finders and infrared pictures may not work dependably. If attic access is available, the most reliable way to locate rafters is from the inside. It is a mistake to assume that rafter layout is consistent center-to-center. Especially in older houses, measure and map each rafter. This will serve as your guide once you are back on the roof. The goal is to make certain that all pilot holes and lag bolts are centered in the rafters, ensuring the best structural connection and minimizing roof penetrations.

If there is no access to the attic, there are several ways to determine where the rafters are located. The nailing pattern on the soffit or fascia, for example, sometimes provides a clue to rafter locations and spacing, even if the rafter tails are not exposed. Invariably, the “high tech” solution that most installers swear by is a hammer or rubber mallet. Bang across the roof, perpendicular to the rafters, noting how the sound changes from hollow to solid to hollow. With a bit of practice, this is often the most reliable way to reveal hidden rafters.

Pitched Roof Racking SolarPro Magazine

Ultimately drilling a small test hole is the only way to be sure you have found a rafter. If your test hole misses, modify a steel coat hanger for use as a probe. Straighten it out and remove any kinks, bend one end of the probe and insert it into the test hole. Gently rotate the probe until it makes contact with the rafter. Getting the bend right requires some experimentation and practice, as does translating that rotation angle to a lateral distance. With time, however, you can dependably find rafter centers with a minimum of drilling.

Once you have located the rafters and mapped out the roof system’s layout, designate a rafter on one end of the roof as the layout’s starting point and drill a hole alongside it. All layout measurements on the roof will reference this point—assuming you can find the hole later. Therefore, immediately push a flag or marker of some kind through the hole. Using a foot or so of folded #12 wire works well for this purpose. A well-sized reference hole makes a tight fit so that the wire stays in place until the layout is complete. As the attachment points are laid out and the pilot holes drilled, mark each location with a flag of some kind. Marking every hole ensures that none are overlooked later when it comes time to seal your penetrations.

Some installers make pilot holes by lifting the leading edge of a shingle and drilling underneath. But water can still find these holes if they are left unsealed. No matter what method of locating rafters and drilling pilot holes you use, do not underestimate the importance of sealing every test hole with an appropriate sealant. Lost or forgotten test holes are a common cause of water intrusion. This is especially true when a roof leaks immediately after an installation is completed.

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