Preparing for PV (article)

ManualsBrandsQuick Mount PV ManualsSolar & Wind PowerFlashing, Classic Composition Mounts, 12" x 12", Mill Finish, QBLOCK

home power 144 • august & september 2011

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PV modules on the roof,” you will most likely get an outdated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.

Before You Start

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.

Installing & Flashing PV Roof Mounts

Story & photos by Johan Alfsen

Prepping for

All photos courtesy Quick Mount PV

Summary of content (6 pages)

PAGE 1
PV Prepping for Installing & Flashing PV Roof Mounts All photos courtesy Quick Mount PV Story & photos by Johan Alfsen 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.
PAGE 2
roof mounts 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.
PAGE 3
roof mounts • Roofing code-compliance— The International Building Code (IBC) calls for flashing to be installed on all roof penetrations. A minimum of 4 inches of flashing should be on each side of the roof penetration to divert wind-driven rain. • Product certification (Example: ICC-ES)—There are product evaluation services such as ICC-ES that perform technical evaluations to determine that products comply with codes and standards.
PAGE 4
roof mounts Sheet Metal & Air Conditioning Contractors’ National Association (SMACNA) states that galvanized flashings should not be installed on roofs that will exceed 15 years. 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.
PAGE 5
roof mounts On a New Roof... For existing roof installations, many PV installers use integrated flashing and mounting solutions as shown above. Many of the same mounting/ flashing products can be used on new roofs after the roof is installed, but standard post and flashing systems are more common on new roofs. Before the roofing is installed, you can attach your stand-off posts and then the roofers can install separate waterproof flashing as they shingle the roof.
PAGE 6
roof mounts Step 3 Attach the post to the base. Secure the post to the base by turning the post onto the captive grade-8 bolt inside the base plate. Step 4 & 5 As the roofers work their way up the roof slope, they will install roofing material around the posts and install the appropriate flashing. This is a common practice, and similar waterproof flashing will be installed around vent pipes and skylights. Step 6 An EPDM pipe collar is installed to waterproof the post-to-flashing connection.