Solar power can be a valuable asset to your building, but only if it’s installed on the right roofing material.
By Tom Utrup, Special to Solar Power World
Building owners, contractors and architects considering a PV installation are often focused only on PV array specification and requirements. But regardless of the building type, age and location, installing solar PV is complex and demands careful consideration of the many inter-related requirements affecting other building components. Foremost of these requirements is the foundation for the entire PV installation — the roof.
Integrating both the requirements of the roof and the PV array from the start — whether the building is an existing structure being retrofitted with PV or new construction — ensures the best renewable energy production and financial rewards.
A typical rooftop PV investment is based on a 25-year financial projection. Therefore, the roof must be able to sustain heavy PV for at least that long to gain the highest possible returns. The best way to achieve this is to combine a heavy-duty, high-performing roof with the appropriate long-lasting PV array. Two recent installations provide examples of how this plays out.
Roofing System Helps Skechers Meet Efficiency Standards
When Skechers wanted to put solar on its 1.8 million-square-foot North American operations distribution center in Moreno Valley, Calif., one of its primary objectives was to make sure all of the building components complied with California Title 24. This is a mandated building energy-efficiency program from the California Energy Commission.
To achieve this, a 15-man crew started by installing a membrane, a protective, waterproofing top layer of a roofing system that prevents leaks. The crew used Firestone Building Products’ UltraPly TPO membrane, which comes in reflective white or tan to reduce a building’s cooling requirements, allowing it to meet the standards for Title 24.
Next, to achieve a Class A fire rating (the highest rating a product can score under the U.S. building code’s ASTM E 84 rating system), the crew installed two layers of fiberglass mat onto the wood deck to provide insulation against heat. The membrane was mechanically fastened over these underlayments, and the field seams were hot-air welded to mirror a FM 1-90 installation pattern, which guards against wind uplifting the roofing system.
The contractor also transferred approximately 670 tons of river rock onto the roof and created 50-foot-wide by 685-foot-long rock ballasts on either side of the walls – all without damaging the roofing membrane. In case of a fire, the rock ballasts help contain flames to the section where they originated.
After deciding on a solar provider, the contractor was back on the roof installing the 808,000-W thin-film PV system. More than 5,600 panels were adhered to the membrane over 220,000 square feet of the roof. Contractors increased the adhesion of the panels with an application of Firestone’s TPO QuickPrime LVOC primer, a solvent-based formulation designed to clean and prime the membrane.
The resulting installation was a success. The distribution center is the largest LEED-accredited industrial-use building in North America.
Manufacturing Plant Gets a Retrofit
It’s no less important to consider the roof in retrofits, such as the one Firestone had put on its own manufacturing facility in Bristol, Conn. The company received a clean-energy grant from the state to update its facility for energy sustainability purposes. The program’s goal was to create concurrent lifecycles between both the roofing and the PV system. Syncing the lifespans of the two systems would enable the highest levels of energy efficiency and savings.
Building owners have a variety of choices of heavy-duty roofing systems, which include thermoplastic polyolefin (TPO), ethylene propylene diene monomer rubber (EPDM), styrene-butadiene-styrene (SBS) modified bitumen and standing seam panel metal systems. For its plant, Firestone used a 90-mil thick white EPDM membrane which reflects sunlight and keeps the membrane cool. This was installed over the company’s half-inch-thick high density ISOGARD HD cover board to protect the roof from potentially damaging effects from weather and foot traffic. Installers topped this with a thermal layer of insulation.
Syncing a roofing system with similar lifespan as your PV or other solar rooftop systems is crucial to minimizing risk and maximizing the value of the investment. All of these considerations are about achieving the best possible building performance and energy-saving ROI. Rooftop solar is a viable alternative for the solar and green building industry. Because rooftop solar arrays require the roofing system to become an integral support for PV, it’s crucial to consider an integrated solution, including partnering with contractors who can install and maintain both systems.
Tom Utrup is with Firestone Building Products Energy Solutions Innovative Products and Services