{"id":432,"date":"2014-01-08T18:41:13","date_gmt":"2014-01-08T23:41:13","guid":{"rendered":"https:\/\/roofingmagazine.com\/?p=432"},"modified":"2014-01-26T13:35:17","modified_gmt":"2014-01-26T18:35:17","slug":"pv-ready","status":"publish","type":"post","link":"https:\/\/roofingmagazine.com\/pv-ready\/","title":{"rendered":"Are You \u2018PV Ready\u2019?"},"content":{"rendered":"

Commercial rooftops are an attractive platform for the installation of solar photovoltaic (PV) electricity-producing systems. These low-slope roofs offer an economical and sustainable structural foundation for renewable solar energy. As an example, one of the largest roof-mounted PV systems in North Carolina has been online for several months at the Old Dominion Freight Line Inc. vault logistics facility in Thomasville. Almost 7,700 solar panels completely cover the warehouse\u2019s 160,000-square-foot roof and produce enough power (1.8 megawatts) to offset more than 90 percent of the building\u2019s annual energy costs.<\/p>\n

Success stories like Old Dominion\u2019s are becoming increasingly common in the sunny Carolinas. However, it is important to remember a roof\u2019s function is, first and foremost, to protect the building\u2019s contents and people from the elements. In this regard, roofing professionals need to anticipate the potential risks associated with the installation of a roof-mounted PV system (array). This sort of due diligence is particularly important when installing PV systems on existing warranted roofs.<\/p>\n

\"A<\/a>

A broad selection of membranes and thicknesses are available for consideration when a PV installation is planned. Photo courtesy of GAF, Wayne, N.J., and Protech Roofing Service, San Diego<\/p><\/div>To help in these industry efforts, members of Waltham, Mass.-based SPRI<\/a>\u2014the trade association that represents sheet membrane and component suppliers to the commercial roofing industry\u2014have developed \u201cPV Ready\u201d roof assemblies and guidelines designed to provide maximum protection for the roof (and maintain its warranty coverage).<\/p>\n

In September, SPRI\u2019s technical committee and board of directors also approved and distributed to its members Technical Bulletin 1-13A, \u201cSummary of SPRI Membrane Manufacturer Photovoltaic (PV) Ready Roof Systems and Services\u201d. The bulletin contains general guidelines from SPRI related to \u201cPV Ready\u201d roof assemblies. This article goes into more depth about issues related to PV installations, particularly on existing warranted roofs.<\/p>\n

Ask the Right Questions<\/h4>\n

The installation of a PV system on an existing warranted roof raises many important questions for the roofing professional and building owner. For example, will the roof accommodate the added weight of the PV array? Logistically speaking, before property owners decide on a solar-power system, they will need to determine whether their roofs are sturdy enough to support
\nthe additional loads put on the existing roof structure by the solar array.<\/p>\n

An average solar panel and support system typically add a minimum of 3 to 4 pounds per square foot to the existing roof. It is the responsibility of the roofing professional to ensure this additional weight does not exceed the load limits determined by the building\u2019s designer.<\/p>\n

From an economic (life-cycle-cost) point of view, it makes sense the service life of the existing roof membrane will come close to matching the projected service life of the PV system. If not, a complex and costly reroofing project may be required long before the solar panels need to be replaced. In general, the underlying roofing system must provide the same minimum investment horizon\u2014generally at least 25 years\u2014to realize the full potential of the rooftop PV system.<\/p>\n

Most PV arrays require penetrating the roof membrane. Even non-rack-type systems may include electrical conduits, wiring and other components that may need to be flashed in a professional manner. It is essential the responsibility for this flashing work rests with the roofing contractor.
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\nIt 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.<\/p>\n

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
\nof three standards for vegetative roofs: ANSI\/SPRI VF-1, \u201cExternal Fire Design Standard for Vegetative Roofs\u201d. 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, \u201cWind Design Standard for Vegetative Roofing Systems\u201d provides design
\nguidelines associated with wind uplift and stone ballast scour.<\/p>\n

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<\/a>

With the installation of rooftop PV, the roofing system becomes more than just a roof\u2014it becomes a permanent platform for the continuous operation, service and maintenance of the PV system. Photo courtesy of Johns Manville, Denver<\/p><\/div><\/p>\n

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\u2019s single-source system guarantees, these documents must be evaluated in detail with the appropriate approvals given by the issuer of the guarantee.<\/p>\n

Roof System Durability<\/h4>\n

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.<\/p>\n

With the installation of rooftop PV, the roofing system becomes more than just a roof\u2014it becomes a permanent platform for the continuous operation, service and maintenance of the PV system. That\u2019s 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.<\/p>\n

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\u2019s 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.<\/p>\n

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\u2019s 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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\nTherefore, the chance of sharp tools dropping onto the roof surface or impact damage from heavy traffic or equipment installation is increased. That\u2019s why enhancing the puncture resistance of membranes used with rooftop PV systems can be so important. Solutions may include protective coverboards when practical or other options for existing roofs, such as roof walkway pads.<\/p>\n

In fact, some roof system manufacturers require an approved insulation board with a minimum thickness and compressive strength, the addition of an approved coverboard to enhance insulation protection, and\/or an approved protection\/separation sheet installed between the PV components and the membrane. Protection pads should be large enough and properly secured so they do not move during expansion and contraction of the roof membrane.<\/p>\n

Membrane Type and Thickness<\/h4>\n

\"The<\/a>

The roof on Old Dominion Freight Line Inc.\u2019s vault logistics facility in Thomasville, N.C., features almost 7,700 solar panels. The panels produce enough power (1.8 megawatts) to offset more than 90 percent of the building\u2019s annual energy costs. Photo courtesy of Old Dominion Freight Line Inc., Thomasville, N.C.<\/p><\/div>
\nA broad selection of membranes and thicknesses are available for consideration when a PV installation is planned.
\nFor example:<\/p>\n