There are online instructional videos to teach just about everything—from playing your favorite guitar riff to installing dual-pane windows. But when you search for “how to mount PV modules on the roof,” you will most likely get an outdated video showing improper roof penetrations that actually void roof warranties and violate roofing codes and standards.
Only in the past few years have manufacturers designed mounting and waterproof flashing systems that are easy to install and meet the codes (see “Modern PV Roof Mounting” in HP137). Here is a step-by-step explanation for installing a code-compliant rack system on a composition/asphalt shingle roof.
Safety & roofing. Working on a roof can be dangerous and OSHA safety standards should always be followed (see www.osha.gov/dep/greenjobs/solar_falls.html). Roof warranties should also be considered. The roof’s condition will need to be evaluated to determine if a new roof will be needed. If not, contact the original roofing company to determine if there are any workmanship and product warranties that might be affected. If a new roof is going to be installed prior to installing the PV system, stand-off posts can be attached, which can then be flashed and waterproofed by the roofers as they install the new roof.
Layout & Attachment. Plan ahead so that you know how many roof penetrations need to be made—prior to stepping onto the roof. Online rack calculators or manufacturer specifications can help determine the proper number of roof attachments needed for your system and location (see Access).
Proper attachment to the roof structure is key to a strong rack system. If possible, it is best to attach additional wood blocking between rafters. When blocking is not an option, then you must pre-drill into the rafter and attach with a lag bolt or hanger bolt. Staggering the mounts on the roof to avoid attaching every rail to the same rafter helps distribute the load.
A common method of finding rafters is to transfer measurement points from inside the attic to the roof. If attic access is not an option, there are other methods and tricks that you can use. Looking at the gutters and bays from the ground, use a mallet to gently knock and determine rafter placement, or use a deep scan rafter finder. As a last resort, you can also use a small (typically 5/32-inch) bit to drill through the roof to find the rafters. If the bit misses the rafter, you can then use a wire coat hanger to fish through the hole and locate the rafter. Be sure to seal any holes you’ve made.
Once the rafter layout is determined, make chalk lines down the roof to mark the rafters and across the roof for your rail placement.
There are a variety of code-compliant mounting and flashing products on the market. Before you buy, consider the following things.
Many manufacturers have this information on their websites. Obtaining a product sample for personal inspection can help verify the quality of the product being used, noting the workmanship, and weight, thickness, and size of the material.
No matter what product you choose, always follow the manufacturer’s installation instructions. Many manufacturers provide installation videos. While they may not teach you how to play your favorite guitar lick, they will certainly help you install code-compliant mounting and flashing solutions for your roof.
Johan Alfsen got his start in the solar industry as an installer. Currently, he is the training manager for Quick Mount PV.
Direct Power & Water • www.dpwsolar.com
EcoFasten • www.ecofastensolar.com
Haticon • www.haticonsolar.com
IronRidge • www.ironridge.com • Rooftop mount configurator
Oatey • www.oatey.com • Flashing
Pro Solar • www.prosolar.com
Quick Mount PV • www.quickmountpv.com
SnapNrack • www.snapnrack.com
TerraSmart • www.terrasmart.com
Thompson Technology Industries • www.thompsontec.com
Unirac • www.unirac.com
Zilla • www.zillarac.com