Monday, February 18, 2013

Roofing Considerations for PV Installers

Residential rooftop solar photovoltaic panels Before beginning your rooftop PV project, the installer must consider many issues. Careful, detailed preparation can prevent cost over-runs, re-doing work and scheduling-delays during a rooftop PV project.  Proper preparation and advance work ultimately means risk reduction for the installer and a more successful and efficient project, not to mention happy customers.
Critical to the detailed preparation for your rooftop solar project, whether it is photovoltaics or solar thermal—is understanding two important levels of “paper work” information: building code requirements and roof system manufacturer requirements for integration of rooftop solar.  This information isn’t necessarily exciting, but it is necessary. Therefore, understanding the requirements will keep you out of trouble and make for a successful project.


Proper preparation and advance work ultimately means risk reduction for the installer.
In the US, the most recent I-Codes (2012 editions) include many requirements for rooftop PV installations.  They can be found in the International Building Code (IBC), the International Residential Code (IRC), and the International Fire Code (IFC).  It’s also important to understand the requirements in NFPA 70, also known as the National Electric Code.  This article will not discuss electrical code requirements.
IBC 2012, which, simply put, is for commercial and industrial buildings, and it includes PV requirements in the roofing chapter.  Chapter 15, Roof Assemblies and Rooftop Structures, includes wind, fire, installation and material requirements for PV installations.
For all types of PV installations, fire-classification requirements are found in sections 1505, Fire Classification.  All other requirements for integrated and rack-mounted PV systems are discussed separately.  Section 1507, Requirements for Roof Coverings, provides requirements for adhered modules (adhered to the roof system) and PV shingles.  Specifically, requirements for materials, attachment and wind are found in section 1505.17.
Commercial rooftop solar installation - CSU Chico, CaliforniaFor rack-mounted systems, requirements are found in section 1509, Rooftop Structures.  Specifically, section 1509.7 includes wind, installation and materials requirements.
Specific test methods are required to be used for PV shingles; ASTM E108 and UL790 are required to be used to determine fire resistance.  ASTM 3161 is required to determine wind resistance of PV shingles.  Panels and modules are required to be labeled with fire and wind resistance information.
Section 1511 ties the IBC to the IFC, where additional requirements for rooftop PV installations can be found.  In general, the requirements in IFC 2012 are about access to and pathways while on a rooftop with a PV installation.  These requirements are for safety and fire fighting for emergency responders.  It’s critical to layout rooftop PV arrays to allow for rooftop safety for anyone accessing the rooftop.
For PV modules adhered to a roof membrane, the fire classification of rooftop PV installations is likely to be determined by the roof system manufacturer.  Rack-mounted panels’ fire resistance comes from the panel and/or rack manufacturer and is separate from the roof system fire rating.  Coordination of the fire ratings should be performed by the rooftop PV designer.
IRC 2012, which essentially covers single-family houses, townhouses and duplexes, not only includes new rooftop PV requirements in the roofing chapter, it also includes new PV requirements for rooftop and ground-mount installations in Chapter 23, Solar Energy Systems.  Overall, rooftop PV requirements are very similar in the IBC and the IRC.
PV systems on rooftops are now mandated by code to be safe for public use.  It’s critically important to understand this as a PV installer.  It’s important to understand the specific building code requirements so, as an installer, you understand when to contact the roof system manufacturer to acquire the proper information for building code compliance.

Roofing manufacturers

It is critically important to understand, first, who the roof system manufacturer is, and second, the attachment and integrations requirements for the PV or solar thermal system required by that manufacturer.
Commercial rooftop solar installation - Kohls, Laguna Niguel, CaliforniaFor example, most roof system manufacturers have minimum requirements for membrane thickness when adhering PV modules.  Roof manufacturers generally require a cover board over the insulation layer (under the membrane) to provide toughness and durability, with the expectation of a longer service life of the roof and PV systems.  This is especially important for the numerous ballasted PV racking systems that are currently being used in the market.
For penetrating PV rack systems, it’s extremely likely a roofing manufacturer will require an authorized system installer to perform the flashing work.  Not only does this help ensure a successful weatherproof installation, it ensures the warranty is not voided (e.g., if non-authorized installers do the work).  Even though maprony roofs are visually similar, not all materials are compatible with each other.  PVC and TPO should not be used together, and the using the wrong material will certainly void the warranty.  The construction detail used at the penetrations also must meet the manufacturer’s requirements.  Contacting the manufacturer and using an authorized installer will help ensure roof system manufacturer acceptance and a continued warranty.
The ultimate goal of a rooftop PV installation is long-term weatherproofing and clean energy production.
You can find a lot of important rooftop PV information on a roofing manufacturer’s website; however, pick up the phone and discuss the PV installation before starting the project.  For example, slip sheets will likely be required, but what kind of slip sheet?  Having to replace non-manufacturer approved slip sheets with appropriate ones is going to be expensive and time consuming.
For PV installations on steep-slope roof systems, find out if the penetrating attachment device is acceptable to the product manufacturer.  Ultimately, the question is: Will the attachment method void the warranty?  This is critical to know before starting the project.
As a rooftop PV installer, regardless if your background is PV or roofing, it is critical to understand code requirements (building, electrical and fire) as well as manufacturers requirements in order to maintain the building or homeowner’s warranty.  It’s also a wise business decision to not void a roof warranty; the cost of roof repairs (or roof replacement) may not be manageable by your company, and no one needs to go out of business due to a lack of proper preparation!
The ultimate goal of a rooftop PV installation is long-term weatherproofing and clean energy production.  Knowing the building code and roof manufacturers requirements will help lead to a successful, long term rooftop PV system.
Written by James Kirby, Vice President of Sustainability, Center For Environmental Innovation in Roofing based in Washington, DC (US)

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