Solar photovoltaic applications in the U.S. continue to grow at an astounding pace, even though the domestic market has tapped only a small portion of the potential PV development.
So far, 2012 has been a strong year for the PV industry, with approximately 2,800 MW of installations projected, according to the Solar Energy Industries Association. The future looks even brighter, with forecasts for PV installations expected to rise at a compound annual growth rate of 30% through 2012.
To compare, the U.S. solar energy industry installed 1,855 MW of photovoltaic solar systems in 2011, representing a 109% increase over 2010. That’s enough to power 370,000 homes. The SEIA reported the fourth quarter of 2011 alone recorded 776 MW of PV systems installed in the U.S., making it the largest installation of photovoltaics for any quarter in PV market history.
Nearly half the installed and planned PV projects in the U.S. are expected to be roof-mounted installations. That’s a scary prospect for roofing product manufacturers and contractors, because an improperly installed PV rack can tear a roof to pieces in no time.
BD+C asked James R. Kirby, Vice President of Sustainability for the Center for Environmental Innovation in Roofing, Washington, D.C., for advice about what Building Teams and building owners should know about roof rack PV systems.
1. DO use the proper flashing techniques for steep-slope roofs.
Because water flows downhill, for steep-slope roofs (which, according to ASTM standard E 1918-97, are roofs in which the uppermost part is installed at a slope of 2:12 or more), proper overlaps during installation are critically important. Commonly used materials for this type of installation are metal flashings with compression gaskets or counterflashing at roof penetrations (or both).
Flashing works because it is located above the level where water drains.
For vertical penetrations, the flashing is the primary weatherproofing element. Counterflashings are secondary and placed above the flashing piece.
7 do’s and don’ts of PV roof rack installation
1. DO use the proper flashing techniques for steep-slope roofs.
2. DO avoid improper flashing techniques for low-slope roofs.
3. DON’T allow for hunt-and-peck pilot holes on steep-slope roofs.
4. DO maintain the roof and PV system after installation.
5. DON’T consider initial payback alone: Factor in life cycle costs.
6. DON’T equate a non-penetrating rack system with zero roof penetrations.
7. DO ask about ballasted rack systems on low-slope roofs and the impact of movement, abrasion, drainage, and wind.
In steep-slope situations where flashing is not feasible or necessary, the counterflashing should extend at least to the nail line of the shingle above. Both methods are acceptable for long-term PV roof rack installation.
“Not all low-slope penetrations use counterflashings, but they all need flashings,” says Kirby. “For steep-slope roofs, it’s a bit different. Shingles basically flash the shingle below by covering up the nails. So if a vertical presentation is attached to a roof, then it needs to be flashed.”
However, in steep-slope roofs, a counterflashing can be inserted under a shingle and over a fastener that’s securing the PV rack.
2. DO avoid improper flashing techniques for low-slope roofs.
For low-slope roofs with little slope to drain, rainwater can pond in low spots or where drainage is interrupted. Drainage can be interrupted by large or wide penetrations or by ballasted PV racks.
It is critical to use flashing that matches the roof’s membrane system. “For low-slope roofs, the flashing material is interfaced with the membrane material, and the materials are not interchangeable,” says Kirby.
Building Teams should support their clients by making sure that the PV contractor incorporates the proper flashing technique for penetrating PV racks.
3. DON’T permit hunt-and-peck pilot holes on steep-slope roofs.
Pilot holes are the number one reason for callbacks for complications after installation. PV installers often use a thin drill bit to locate a rafter in order to position the attachments. Unfortunately, they don’t always repair their “investigation” holes. There are ways to repair these pilot holes, but it’s best not to “hunt-and-peck” in the first place.
“Rafters should be located by observing the eave and ridge,” says Kirby. “Locate nails in the fascia board, which is commonly nailed into the ends of the roof rafters.”
Caution: Vertical stanchions generally require one or two fasteners to be installed into the rafter, not the roof deck, in order to achieve proper pull-out resistance to wind uplift.
4. DO maintain the roof and PV system after installation.
A roof’s chief priority is to keep water and weather out of the building. Therefore, the ability to perform maintenance is critical to the long-term success of a low-slope roof. Certain styles of ballasted PV racks can make it difficult to perform roof maintenance. Some styles must be removed or relocated in order to get to the roof surface for maintenance.
Fortunately, a number of newer rack styles and types that recognize the need for roof maintenance have been developed. “Those styles and types of PV systems will be the long-term success stories in the rooftop PV industry,” says Kirby. “Roof-friendly racking systems are a relatively new trend, and it’s up to the roofing industry to push for more roof-friendly racking systems.”
5. DON’T consider initial payback alone: Factor in life cycle costs.
It’s not easy getting most building owners to think long-term, but Building Teams should counsel clients about the PV investment in the cost per year over the 25- to 30-year life of the roof and the PV system.
According to Kirby, a building owner may expect a relatively short-term payback from the PV system in a certain number of years, but the owner also needs to recognize that the inverter will likely have to be replaced at year 12 or 15.
And what about the cost of a roof replacement if it’s not done at the time of installation? The age of the roof must be considered at the time of PV installation because it’s critical to the long-term success of both the roof and the PV installation.
“A roof that is too old could mean that the PV system may have to be removed along with the old roof,” says Kirby. “If the owner didn’t prepare for the cost, the PV system may not be installed again.”
6. DON’T equate a non-penetrating rack system with zero roof penetrations.
A building owner may be buying a non-penetrating PV rack system, but how do the PV system’s electrical lines get into the building? According to Kirby, the answer is often “through the roof.”
A junction box may be supported by non-penetrating supports; however, this does not eliminate the penetration caused by electrical lines. The entry point for the DC conduit must be properly flashed. Therefore, most if not all PV systems will have at least one penetration.
The same premise is true for both types of non-penetrating systems––adhered and ballasted. It is also important to note that if the PV installation is to occur on a low-slope roof that is under warranty, a contractor recommended by the roofing membrane manufacturer is required in order to keep the warranty from being voided.
7. DO ask about ballasted rack systems on low-slope roofs and impact of movement, abrasion, drainage, and wind.
There are critical questions you should ask the PV contractor prior to installation:
- How does a ballasted PV system rest upon the roof assembly?
- What will happen over time on the rooftop where the ballasted system meets the roof surface?
- Will it collect water and eventually cause weakness?
- Will there be dust or debris between the roof surface and the bottom of the rack?
- Will dust or debris abrade the roof surface over time?
- What measures can be taken to protect the integrity of the roof at the point of contact?
According to Kirby, asking these questions prior to installation is important because any problems that occur may reduce the return on investment to the property owner, while proper installation will keep maintenance costs in check over the life of the rooftop PV system. +
Related Stories
| Dec 17, 2010
Historic Rhode Island hotel reborn with modern amenities
The iconic Ocean House resort in Watch Hill, R.I., had to be torn down in 2005 when systemic deficiencies made restoration unfeasible. Centerbrook Architects and Planners, Centerbrook, Conn., designed a new version of the hotel, working with preservation societies to save or recreate favorite elements of the original building, and incorporating them into the contemporary structure. The new resort has 49 guest rooms and 23 residences, plus banquet halls, a corporate boardroom, a private clubroom, a spa and fitness center, an indoor lap pool, a bar, and the obligatory international croquet court. Dimeo Construction, Providence, R.I., was the construction manager.
| Dec 17, 2010
Gemstone-inspired design earns India’s first LEED Gold for a hotel
The Park Hotel Hyderabad in Hyderabad, India, was designed by Skidmore, Owings & Merrill to combine inspirations from the region’s jewelry-making traditions with sustainable elements.
| Dec 17, 2010
Condominium and retail building offers luxury and elegance
The 58-story Austonian in Austin, Texas, is the tallest residential building in the western U.S. Benchmark Development, along with Ziegler Cooper Architects and Balfour Beatty (GC), created the 850,000-sf tower with 178 residences, retail space, a 6,000-sf fitness center, and a 10th-floor outdoor area with a 75-foot saltwater lap pool and spa, private cabanas, outdoor kitchens, and pet exercise and grooming areas.
| Dec 17, 2010
Sam Houston State arts programs expand into new performance center
Theater, music, and dance programs at Sam Houston State University have a new venue in the 101,945-sf, $38.5 million James and Nancy Gaertner Performing Arts Center. WHR Architects, Houston, designed the new center to connect two existing buildings at the Huntsville, Texas, campus.
| Dec 17, 2010
Alaskan village school gets a new home
Ayagina’ar Elitnaurvik, a new K-12 school serving the Lower Kuskikwim School District, is now open in Kongiganak, a remote Alaskan village of less than 400 residents. The 34,000-sf, 12-classroom facility replaces one that was threatened by river erosion.
| Dec 17, 2010
Luxury condos built for privacy
A new luxury condominium tower in Los Angeles, The Carlyle has 24 floors with 78 units. Each of the four units on each floor has a private elevator foyer. The top three floors house six 5,000-sf penthouses that offer residents both indoor and outdoor living space. KMD Architects designed the 310,000-sf structure, and Elad Properties was project developer.
| Dec 17, 2010
Subway entrance designed to exude Hollywood charm
The Hollywood/Vine Metro portal and public plaza in Los Angeles provides an entrance to the Red Line subway and the W Hollywood Hotel. Local architect Rios Clementi Hale Studio designed the portal and plaza to flow with the landmark theaters and plazas that surround it.
| Dec 17, 2010
New engineering building goes for net-zero energy
A new $90 million, 250,000-sf classroom and laboratory facility with a 450-seat auditorium for the College of Electrical and Computer Engineering at the University of Illinois at Urbana/Champaign is aiming for LEED Platinum.
| Dec 17, 2010
Vietnam business center will combine office and residential space
The 300,000-sm VietinBank Business Center in Hanoi, Vietnam, designed by Foster + Partners, will have two commercial towers: the first, a 68-story, 362-meter office tower for the international headquarters of VietinBank; the second, a five-star hotel, spa, and serviced apartments. A seven-story podium with conference facilities, retail space, restaurants, and rooftop garden will connect the two towers. Eco-friendly features include using recycled heat from the center’s power plant to provide hot water, and installing water features and plants to improve indoor air quality. Turner Construction Co. is the general contractor.
| Dec 17, 2010
Toronto church converted for condos and shopping
Reserve Properties is transforming a 20th-century church into Bellefair Kew Beach Residences, a residential/retail complex in The Beach neighborhood of Toronto. Local architecture firm RAWdesign adapted the late Gothic-style church into a five-story condominium with 23 one- and two-bedroom units, including two-story penthouse suites. Six three-story townhouses also will be incorporated. The project will afford residents views of nearby Kew Gardens and Lake Ontario. One façade of the church was updated for retail shops.
