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
| Nov 3, 2010
Public works complex gets eco-friendly addition
The renovation and expansion of the public works operations facility in Wilmette, Ill., including a 5,000-sf addition that houses administrative and engineering offices, locker rooms, and a lunch room/meeting room, is seeking LEED Gold certification.
| Nov 3, 2010
Sailing center sets course for energy efficiency, sustainability
The Milwaukee (Wis.) Community Sailing Center’s new facility on Lake Michigan counts a geothermal heating and cooling system among its sustainable features. The facility was designed for the nonprofit instructional sailing organization with energy efficiency and low operating costs in mind.
| Nov 3, 2010
Seattle University’s expanded library trying for LEED Gold
Pfeiffer Partners Architects, in collaboration with Mithun Architects, programmed, planned, and designed the $55 million renovation and expansion of Lemieux Library and McGoldrick Learning Commons at Seattle University. The LEED-Gold-designed facility’s green features include daylighting, sustainable and recycled materials, and a rain garden.
| Nov 3, 2010
Recreation center targets student health, earns LEED Platinum
Not only is the student recreation center at the University of Arizona, Tucson, the hub of student life but its new 54,000-sf addition is also super-green, having recently attained LEED Platinum certification.
| Nov 3, 2010
New church in Connecticut will serve a growing congregation
Tocci Building Companies will start digging next June for the Black Rock Congregational Church in Fairfield, Conn. Designed by Wiles Architects, the 103,000-sf multiuse facility will feature a 900-person worship center with tiered stadium seating, a children’s worship center, a chapel, an auditorium, a gymnasium, educational space, administrative offices, commercial kitchen, and a welcome center with library and lounge.
| Nov 3, 2010
Senior housing will be affordable, sustainable
Horizons at Morgan Hill, a 49-unit affordable senior housing community in Morgan Hill, Calif., was designed by KTGY Group and developed by Urban Housing Communities. The $21.2 million, three-story building will offer 36 one-bed/bath units (773 sf) and 13 two-bed/bath units (1,025 sf) on a 2.6-acre site.
| Nov 3, 2010
Designs complete for new elementary school
SchenkelShultz has completed design of the new 101,270-sf elementary Highlands Elementary School, as well as designs for three existing buildings that will be renovated, in Kissimmee, Fla. The school will provide 48 classrooms for 920 students, a cafeteria, a media center, and a music/art suite with outdoor patio. Three facilities scheduled for renovations total 19,459 sf and include an eight-classroom building that will be used as an exceptional student education center, a older media center that will be used as a multipurpose building, and another building that will be reworked as a parent center, with two meeting rooms for community use. W.G. Mills/Ranger is serving as CM for the $15.1 million project.
| Nov 3, 2010
Chengdu retail center offers a blend of old and new China
The first phase of Pearl River New Town, an 80-acre project in Chengdu, in China’s Wenjiang District, is under way along the banks of the Jiang’an River. Chengdu was at one time a leading center for broadcloth production, and RTKL, which is overseeing the project’s master planning, architecture, branding, and landscape architecture, designed the project’s streets, pedestrian pathways, and bridges to resemble a woven fabric.
| Nov 3, 2010
Rotating atriums give Riyadh’s first Hilton an unusual twist
Goettsch Partners, in collaboration with Omrania & Associates (architect of record) and David Wrenn Interiors (interior designer), is serving as design architect for the five-star, 900-key Hilton Riyadh.
| Nov 3, 2010
Virginia biofuel research center moving along
The Sustainable Energy Technology Center has broken ground in October on the Danville, Va., campus of the Institute for Advanced Learning and Research. The 25,000-sf facility will be used to develop enhanced bio-based fuels, and will house research laboratories, support labs, graduate student research space, and faculty offices. Rainwater harvesting, a vegetated roof, low-VOC and recycled materials, photovoltaic panels, high-efficiency plumbing fixtures and water-saving systems, and LED light fixtures will be deployed. Dewberry served as lead architect, with Lord Aeck & Sargent serving as laboratory designer and sustainability consultant. Perigon Engineering consulted on high-bay process labs. New Atlantic Contracting is building the facility.
