Rooftops are great for solar, but only when important considerations are addressed
By Tony Ruffine
As North America’s largest roofing manufacturer, we know that rooftops are a great location for solar. Roofs are out of the way, tend to have the least shade on a property, are close to utility hookups and usually do not need additional infrastructure. As a result, approximately 80% of solar installations take place on roofs. We have worked closely with the solar industry for several years and are big advocates of rooftop solar.
Working with the best players in the industry, we have seen some great solar projects on top of our roof systems. Unfortunately, many solar buyers and installers do not understand the interplay between the roofing system and solar. Most of us have heard a job sold with some variation of the line: “There are no penetrations so it does not affect your roof warranty.” When we at GAF hear that, we can be almost certain there will be a problem.
Choosing the Right Installer
A lot of solar installers take the roofing piece for granted or do not have the experience with roof top installations to understand the challenges of each roof. That is why choosing an EPC that is familiar with the roof, such as Advanced Green Technologies, is crucial. The property owner should insist on a solar installer with genuine roofing experience. Here are some tips for choosing a qualified solar installer:
• Ask the installer about other rooftop installations they have completed.
• Make sure the installer is respected by roofing-system providers.
• Ensure the company has installed solar on multiple roofing systems using a variety of technologies.
• The installer should be able to discuss rooftop conditions, know how the roof drains, have a strong familiarity with wire management plans, provide roof replacement and repairs, take down and re-install a system during roof replacement and repair and can provide follow up maintenance services.
If a property owner is considering solar, the roof system should be designed with the future installation in mind. Design considerations like slope or placement of drains and scuppers should be done to allow maximum solar coverage. The roof system should also be chosen to support solar. High-density cover boards, for example, should be used when solar will be installed.
Membrane systems should not be loosely laid or mechanically attached, but should be fully adhered. Higher performance membranes provide cheap insurance up front. Walkway pads should be used around the solar (and slip sheets are usually recommended underneath). Most importantly, the roof installation needs to be staged to facilitate the solar installation, considering both schedules.
Common Installation Problems
A successful solar installation is not just one that generates the required amount of electricity. It also has to leave the building in serviceable condition. There is no such thing as a good solar installation on a leaky or damaged roof. Even today, in states where there is a long history of solar installations, we see problems when the solar installer did not understand or take into account conditions on the roof. A few of these problems seem to come up repeatedly:
1. Not matching the roof life to the solar installation’s life. This one should be obvious. A solar installation may generate power for 20 years or more and have financing or PPA lengths just as long. Putting a solar installation that may last 20 years on a roof that, like many new construction roofs, is only designed to last 10 years is asking for problems. A variety of roof systems, however, can last 20 years. Also, membranes are designed for conditions on solar rooftops and so can be warranted for 35 years. Membranes are the protective, waterproofing top layer of a roofing system.
2. Not matching the roof design to solar. Because solar has specific performance criteria, there are points to consider when choosing a roof system to ensure the best solar performance. Solar panels, for example, tend to work best in cooler environments, so a cool membrane can provide better electrical output. Roof systems are also not usually designed for the weight of solar projects or for the foot traffic that installation and maintenance can bring. Understanding the roofing membrane is even more important when considering the potential for directly attached panels in the future. Many membranes will have compatibility issues with these designs. Ensuring the roof is solar-ready up front will avoid a lot of unnecessary work in the future.
3. Not understanding the flow of water. A good roof system should drain water away from the rooftop and shed it away from the building. But racking and wire harnesses can inhibit water flow, preventing water from draining in a timely manner. Even worse, water may be forced in the wrong direction, causing a leak. We have also seen drains clogged when cheap ballast disintegrated and ran out of the ballast tray. Repairs can be more difficult when solar is installed, so it’s important to take account of these concerns up front.
4. Not considering thermal movement or wind/seismic events. We recently visited a rooftop solar installation with 250-ft long racks and no slip-sheets. The rate of thermal expansion on these racking systems was about 0.25%, which means the racks could be moving a little over a foot with each thermal cycle. We have also seen systems damaged from wind because the ballast was not properly installed and the system moved. Taking precautions during installation will avoid many problems.
5. Not understanding rooftop conditions during installations. A good roof system is durable, but it’s not designed to be used as a construction site. Dragging panels or racking across the membrane will damage even the heartiest roof. Dropping tools can penetrate roof membranes. Debris will clog drains or cause other problems. We have seen staging areas on new roofs look like they were 15 years old by the time the solar installation is complete. While this problem was more common a few years ago, seeing roofs torn up from solar installation is still too common.
6. Not having a maintenance plan. Basic maintenance and inspections are necessary on commercial roofs without solar, and the need for maintenance is heightened when solar is installed. We have seen some solar installations with plants growing around panels, and others that end up in the water when a drain clogs. Crews that are used to finding problems with roofing and solar help avoid problems up front and catch other small problems before they become big issues.
Many other rooftop issues can arise with solar. As new installation methods are developed, their effect on the roof system must be seriously considered.
Roofing and solar make a lot of sense together. In the future, we expect the roof and solar integration to become much easier. Forward thinking property owners and solar buyers will wisely choose the right solar installer, select the right roofing materials and design a robust roof system to guarantee the best performance from any solar installation. SPW
Tony Ruffine is vice president of GAF, a North Americian manufacturer of commercial and residential roofing. The company was founded in 1886 and is currently headquartered in Wayne, N.J.