Are You ‘PV Ready’?

It is also important to ensure the positive drainage designed into the existing roof system is not compromised. The use of a tapered insulation system or relocation/addition of new roof drains are two solutions, but these are often cost-prohibitive options for the property owner. In addition, an existing drain partially covered by a solar array will make it difficult to clean out.

Roof system wind and fire code approvals have always been active topics within SPRI, and the increasing popularity of PV and vegetative roofs adds another layer of complexity when attempting to meet codes and standards. In 2010, ANSI approved the first
of three standards for vegetative roofs: ANSI/SPRI VF-1, “External Fire Design Standard for Vegetative Roofs”. This standard will also be included in the 2015 edition of the International Building Code. A second SPRI vegetative roof standard was approved by ANSI on June 3, 2010. ANSI/SPRI RP-14-2010, “Wind Design Standard for Vegetative Roofing Systems” provides design
guidelines associated with wind uplift and stone ballast scour.

It is likely the roofing industry will also need to investigate and standardize wind and fire code designs for PV roof systems. In the meantime, roofing professionals must use care when installing a PV array over an existing roof that carries FM Class 1, UL Class A, or other fire and/or wind classifications. In new construction applications, code compliance is the responsibility of the designer of record. When installing a PV array on an existing roof, contractors should consult the roof system manufacturer to ensure existing codes are met.

With the installation of rooftop PV, the roofing system becomes more than just a roof—it becomes a permanent platform for the continuous operation, service and maintenance of the PV system. Photo courtesy of Johns Manville, Denver

With the installation of rooftop PV, the roofing system becomes more than just a roof—it becomes a permanent platform for the continuous operation, service and maintenance of the PV system. Photo courtesy of Johns Manville, Denver

Existing roof system manufacturer guarantees are an equally important topic. On older roofing systems there may be a variety of roofing manufacturers represented. Even with the popularity of today’s single-source system guarantees, these documents must be evaluated in detail with the appropriate approvals given by the issuer of the guarantee.

Roof System Durability

Roof durability directly affects the sustainability of any roof system and has become a major factor in the choice of the entire roof assembly. At the same time, the potential benefits of the rooftop PV system itself offer long-term energy independence and environmental sustainability. Because the unique challenges of matching PV systems to compatible roofing systems are so important, the building owner needs assurance the combined rooftop PV system is designed, installed and maintained for optimal economic and environmental benefit.

With the installation of rooftop PV, the roofing system becomes more than just a roof—it becomes a permanent platform for the continuous operation, service and maintenance of the PV system. That’s why the roofing system should be designed to minimize the need for major repairs or replacement that could compromise the continuous operation of the rooftop PV.

Because many commercial PV roofing installations are financed using long-term Power Purchase Agreements (PPAs), a financial arrangement between a third-party that owns, operates and maintains the PV system and a host who agrees to place the PV system on his or her property and purchase the system’s electric output for a predetermined period, the continuous, undisrupted generation of solar power is critical to the fulfillment of the terms of the PPA. As a consequence, the margin of safety required in the design, installation and maintenance of the roof may likely exceed normal expectations and minimum standards for commercial roofing systems.

Raised-panel and membrane-integrated PV systems often cover the majority of the roof surface, and both systems require regular inspections and maintenance. Fortunately, today’s PV racks can be changed out fairly easily, which can be a big advantage. Indeed, the frequent need for solar roof inspections and maintenance means the amount of foot traffic on these systems may be far greater than the traffic generated by an occasional piece of HVAC equipment on the roof.

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About Mike Ennis, RRC

Mike Ennis joined SPRI in 1993. He has chaired a variety of SPRI committees and task forces and served as president from 2004-06. He became technical director of SPRI in 2007.

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