The Challenge of Rooftop Solar
Sound waterproofing practices are not a recent innovation. Professional roofers have been taking proven, and often painstaking measures to prevent the possibility of leaks for decades. What is new with solar is the need to make dozens of penetrations in a roof, not just the few needed for an air conditioner or chimney. Making a solar installation economically feasible necessitates a fast way to mount the array while simultaneously ensuring waterproof penetrations.
Those who pioneered off-grid solar installations back in the 1980s didn’t yet realize the need for a proper waterproofing solution. Securing an array to a roof typically involved nothing more than drilling a hole through the roof and into the rafter, filling it with sealant, then bolting down the L-foot.
Getting Beyond Just Sealant
What was unknown to solar installers back then was that the sealants being used were susceptible to breakdown from the sun’s ultraviolet rays, oxidation, expansion and contraction with changing temperatures, and small but frequent physical movements of the bolt over the years due to the thermal expansion and contraction of the rails, plus wind and other vibrations. As the silicone got damaged over time, this one and only form of waterproofing for the array was likely to be compromised.
We've come a long way since those early days. While there are still too many solar installers with insufficient roofing knowledge using unsatisfactory waterproofing products and methods, most solar system designers and installers today recognize the critical importance of following best roofing practices. And local building inspectors in most jurisdictions now require that rooftop solar installations be properly flashed and waterproofed in accordance with state and local roofing codes.