In an ideal world, a homeowner or building owner would consider a roof and solar array as a single unit with a comparable shelf life. One could expect the solar array to last the same length of time as the roof. In today's reality, too many 30-year solar arrays are being installed on roofs with only 10 years or less of useful life left. The roof begins to leak because of age or even damage resulting from a not-thoroughly thought out solar array installation. The array has to be removed, the roof replaced, and the array reinstalled, all at additional cost and time lost. There are many steps to a successful solar array installation; however, the most critical first step is determining if your roof is suitable for an array.
- Most roof types are a candidate for solar, including tile, asphalt, membrane, metal (standing seam metal roof (SSMR)) and shingles.
- SSMR panels are, by design, excellent candidates. The vertical rib formed by the joining of each adjacent panel allows attachment of the array without penetrating the roof. However, not all SSMR panels are designed for clamping accessories to the ribs. Verify with the roofing contractor that your roof panel fits into the “okay” category and that a non-penetrating clamp will fit properly. Alternative roofing clamps with set screws may cause expensive roof damage and void the roof panel warranty. You could also wind up with an array with insufficient wind uplift capability to meet the local building codes.
- Most other types of roofs require supports that penetrate the roof cover and fasten into the roof structure. These penetrations can result in leaks if not installed and flashed correctly.
- Once the type of roof has been determined, have the roofing contractor assess the roof condition for the following:
- Age of roof versus its expected useful life.
- Is the roof and structure capable of withstanding the new dead load of the array plus the additional rooftop equipment, if any, plus the code required snow loads.
- If a new roof is planned, there may be solar-ready installation instructions designed so that the roof will accept the array and maintain the roof warranty.
- Many roof systems carry manufacturer-issued warranties, which likely include provisions for voiding the warranty if any alterations are made without the manufacturer’s prior approval.
- The contractor should be involved with the PV installer in attaching the array to assure that the roof system warranty hasn’t been voided.
The above steps will ensure you match the roof’s life to the expected life of the solar array. You should next make sure that your roof and the array, as a system, meet the local building code requirements for wind uplift and snow loads, especially if you live in a high wind zone area.
Up until recently, the building codes dealt primarily with the roofing systems, and contractors had an abundance of information for roofs that had been tested to meet wind uplift pressures for any wind zone. This includes High-Velocity Hazardous Zones (HVHZ) coastal zones surrounding Florida’s coast and the Caribbean. Not much was available for solar panels and especially the mounting systems until the last few years, and, as usual, as the science changes, the code requirements change and are updated every few years.
Your roof contractor should be familiar with the roofing code requirements as tested per Factory Mutual Approval Standard 4470 or 4471, as well as Underwriters Laboratories UL 580 or 1897. Some local jurisdictions, such as Miami Dade, Fla., have additional requirements that roof systems must meet for structural components, fasteners, and roof covers.
Your solar installer should be well versed with the requirements for the PV panels as tested in UL 1703 “Flat-Plate Photovoltaic Modules and Panels,” which defines requirements for construction, performance, rating, testing, and marking of the modules. UL 2703 covers requirements for clamps, racking and retention systems, and ground lugs for use with the PV modules. Tests for fire resistance and mechanical load testing are now included, along with corrosion resistance in 2703.
An in-depth discussion of the relevant codes is for another day. The roof and the solar array are a partnership that and should be treated as such. The “NRCA Guidelines for Rooftop-Mounted Photovoltaic Systems–Second Edition” is an excellent resource for the roof contractor and PV installer.
Caroll Marston is an engineer with AceClamp, a PMC Industries Inc. company, Plainville, Conn. For more information, visit www.aceclamp.com.