Rooftop Solar Installations

 









By Ralph Velasquez

Director, Sustainable Technologies Group, Tremco, Inc.

In this column I want to tackle the issue of roofing as it relates to Photovoltaic installations. Better known as PV or solar, these installations have taken on new importance as the new administration has settled in. Legislation and economics around the country have begun to make these types of sustainable options more economical. This column will not focus on whether this makes sense or not, but will focus on the less glamorous side of the house, dealing these issues as they relate to roofing in solar applications.

Maintaining Roof Watertightness
There are few key things to consider when weighing the option of going solar. The first is the issue of roof watertightness. In other words, making sure you keep the roof from leaking or being damaged during or after the installation of bright new, shiny energy panels. We have two basic technologies to consider: panels and thin film adhered to the membrane. First let's review panel installations.

When panels are installed, keep in mind the multiple penetrations that will be required in order to support the panel and the racks they sit upon. The preferred solution is to have a professional roofing contractor install a proper curb and flashing system. The second best alternative is to install a pitch pocket with a rain hat as detailed in the National Roofing Contractor's Association (NRCA) roofing manual. A third option is to install a pipe wrap flashing of some type. This third option is the least costly and the least desirable. Since flashings are typically where roofs leak first, it makes sense to call upon professionals to build the best flashing detail possible with high quality materials. Anything less then good design, quality materials and professional workmanship will only be a source for leaks, damage, headaches and, in the worst case, a court case in everyone's future.

When you are considering the use of a building integrated Photovoltaic system, known as a BIPV installation, then flashings on curbs are replaced by critical tie-in seams of some type.
Somewhere in the installation, the BIPV cell must interface to the ply or sheet good and be adhered to the roof membrane below. In some applications the roof below is cut so that the wiring can be passed through to the underside of the deck, here the outside seam tie-in to the roof is even more critical to be watertight. Though non-penetrating solar applications will not be addressed in this column, note they also have interface requirements. Nothing put on a roof is devoid of interface requirements and issues.

Weight Loads
In addition to flashings, it is important to consider the weight loads that these types of systems will impose on the roof deck and the membrane. Panel systems and their support structures can add significant weight, and considerations must be given to potential deck deflection. If deflection occurs, then stress to the roof membrane will be experienced. Deck deflection can cause water to collect and pond, causing a host of roof challenges and, of course, in the worst case situation, a roof collapse could occur. By design, BIPV systems are much more lightweight, but they still add some weight. Therefore, it's important to make sure you are aware how much a system weighs and what, if any, impact this will have on the roofing system.

Wind Loads
Panels will obviously be more likely to catch the wind. Therefore another important consideration is the wind loads that solar panels will impose on the roof system. The system chosen must be carefully evaluated for this impact, especially when looking at the ballasted systems. There have been cases where the ballasted system did not stay in place under less then advertised designed wind conditions. There can also be problems for thin film applications if adhesion of the film is inadequate for the wind zone of the installation. Any panel system not properly anchored can become a sail. So pay close attention to the force of wind on your selected PV system.

Foot Traffic and Ongoing Maintenance
Consider the issue of foot traffic required for servicing of the PV array. Mechanics will be required periodically to access the roof to maintain the PV array. How will they do this? Where will they walk? How often? What tools will they bring and can these tools cause damage to the roof system? In addition to PV maintenance, how are you going to conduct roof maintenance with the PV array in place? The roof will require ongoing maintenance and now you will have something in the way. So have a plan on how to handle this anticipated work.

A related issue is the idea of heat build-up. What doesn't generate power will generate heat and where does this go? If attached as in a BIPV installation it could be driven into the roof system and therefore require the roof to be maintained more often, as heat and UV is an enemy of all roof systems.  Panel applications also impact by heat build-up, just not as much since they are elevated. They also put various strains of hot and cooler shaded spots on the roof, causing various levels of roof expansion and contraction. Ballasted systems are also closer to the roof surface and have higher heat impact on the roof membrane. The bottom line is that it's important to plan for how you are going to address these variables.

Maintaining the Roof Warranty
Let's move on to the roof warranty issues. If the roof is an existing assembly, then contact the holder of that warranty before you install the PV array to make sure you do not violate the terms of that warranty. The manufacturer will have very specific ways they want you and the contractor to treat this roof if you want to keep your warranty intact. It goes without saying to get everything in writing. Make sure you are clear on maintenance requirements and who is responsible for what if something on the roof is damaged by a component of the PV array.

Take into consideration unusual weather events such as hail, tornados, hurricanes, earthquakes, high winds, etc. How does your roof warranty handle these issues and how will it handle them if a PV array is installed?

Codes and Safety
Simple statement here: make sure your array meets all current standards for fire, wind and electrical. How do these codes interface with your roof code requirements? Make sure the PV and roofing installer follow OSHA requirements.

Be "Roof Ready"
A big issue in the marketplace is that in the rush for solar installations, as desirable as this is, there are many buildings where the building is not "roof ready." In other words, PV arrays are being installed over roof systems that will not last anywhere near as long as the array will last. The NRCA publishes that the average commercial roof lasts 17 years, while the average PV array today will last 20-30 years. Even the old PV arrays lasted 20-25 years so we have a mismatch here. 

I have talked to owners who want to put a PV array on roof systems that will not make five more years, let alone 20, and they have not considered the costs of upgrading their roofs before they install the array. If you think roofing is expensive now, think what the cost of that roof removal will be in three, five or 10 years when the entire array will need to be removed or at best worked around, as the old roof has to be removed. Think of the damage that could be done to PV equipment that needs to be removed from the roof, set aside and re-installed later. Experience tells me that a lot of damage could occur and then the roof replacement project will get real interesting at that point.

To avoid this, make sure you have a quality roof, preferably with redundancy built in to the system. Make sure the roof is designed to accommodate maintenance and future removal if the array outlasts the roof system selected. If you are considering a PV installation on an existing roof, have a roof professional exam the roof to look for instances of damaged membrane, water intrusion into the insulation layer, flashing deterioration, poor drainage or any number of concerns that would need to be addressed before an array should be installed. 

If you are in a state where PV still does not make economic sense, then take this opportunity to get your roof "PV ready" so that when the incentives, the technology or the cost of energy makes it viable, you are ready to pounce on the opportunity without the added costs of dealing with the roof at the same time.

So what if PV is never a good choice for you and you got your roof "PV ready?" Then all you did was make an incredibly good economic decision to extend the life of your roofing asset, lessening the impact on landfills, promoted the use of less virgin resources required for a new roof, probably increased energy efficiency through removal of wet insulation or reflective coatings and kept your building dry for less cost per year. Sounds like a pretty sustainable thing to do in my book!

Reprinted by permission of Greenroofs.com.

Ralph Velasquez is the Director of the Sustainable Technologies Group for Tremco Roofing and Building Maintenance.  He has been involved in the construction industry for over 30 years. During his career, Ralph has worked on millions of square feet of roofing and reroofing projects nationwide, as well as a large number of building envelope restoration projects. He has been involved with ASTM subcommittee for Sustainability since 2003 and the Green Roof task force group. Ralph also chairs the subcommittee for Life Cycle Costing, established by the Green Roofs for Healthy Cities. Ralph can be reached at 877-510-2681 or rvelasquez@tremcoinc.com.