On a Commercial Roof, Should My Solar Arrays Be Ballasted or Attached?

Ballasted vs. AttachedAt first glance, using a ballasted solar racking system seems like an easy choice because there will be no roof penetrations. However, depending on the structure of your roof and other environmental factors such as wind, an attached racking system may be a better choice, and possibly  less expensive.

First, know that an experienced solar installer like REC Solar will have a structural engineer assess your roof for the suitability of either racking system.

Are your rafters strong enough to handle the extra weight of a ballasted system?

How old is the roof?

What type of roofing membrane is it, and can a racking system be attached to it instead of rafters?

Beyond that, our solar PV designers will have to consider any existing roof obstacles, such as air conditioners, vents, and satellite dishes, as these may also affect your racking choices.

With that in mind, let’s look at each type of commercial roof racking system’s advantages and disadvantages.

Ballasted Solar Racking Systems

Advantages:

  • Few to no roof penetrations. The clear primary advantage to ballasted solar racking systems is that they don’t penetrate the roof…in general. However, there are some hybrid ballast systems that will need some type of physical attachment to the roof, although there will be fewer penetrations than a fully attached racking set. In addition, if your building is in an earthquake zone, seismic codes will require some minimum attachments.
  • Faster to install. Without the extra care and logistics of roof penetration hardware, fully ballasted installations can be easier and faster to install, thus reducing labor costs.
  • Typically lower profiles. For customers that want solar panels to minimally affect the roofline’s appearance, ballasted systems can be more discreet because they’re usually installed with a lower angle, so as to minimize wind shear.

Disadvantages

  • Heavier weight on the roof. By their nature, ballasted racking systems will be heavier than attached systems. Not all roofs will be able to support the extra weight, so a structural engineer will have to perform a thorough evaluation during your site analysis.
  • Potentially more expensive. The costs for ballasted systems and components can be more than attached racking systems. However, depending on the experience of the solar installer, this extra expense may be offset by a faster installation, which will lower the labor costs.
  • Less flexible. Ballasted systems can be very kit-like, not allowing for much flexibility. That inflexibility means engineers will have to find more creative work-arounds for an odd roof shape, uneven roofs, and rooftop obstacles, such as HVAC units.
  • Roof maintenance may be more difficult. Because ballasted systems can be less flexible in their designs, they may impede access to panel cleaning and maintenance if modules are positioned too close together. If there’s more space between rows of modules, then there will be less room on the roof, and hence fewer solar panels may be installed.

Attached (Roof Penetrating) Commercial Solar Racking

Advantages

  • Lower product and component costs. While more skilled labor is needed to install a non-ballasted system, there’s typically a lower upfront cost for the racking and components.
  • More flexible. Because attached roof racking structures are less of an all-in-one solution, it can be more flexible for working around roof obstacles, such as HVAC units, vents, satellite dishes, water towers, etc.
  • Potentially more solar panels on the roof. Attached racking can be more customized, so solar engineers may be able to squeeze in more solar panels, and therefore, the customer may be able to harvest more energy.

Disadvantages

  • Roof penetrations. In order to anchor the racking system to the roof, the roof will be penetrated with multiple large screws that not only go through the roof, but may also have to be attached to internal building structures. Of course, an experienced installer like REC Solar will properly use the manufacturer’s flashing, as well as other water sealants so that no leaks trickle into the building structure.
  • Higher labor costs. Attaching the solar racking to the roof requires more skilled labor in order to prevent leaks. It will also need more scrutinized safety and quality inspections, adding to the cost.
  • More involvement with the roofing manufacturer and other roof stakeholders. Because you’ll be penetrating the roof, the roofing manufacturer and original roofer will want to be involved in order to preserve the remaining years left of the roof’s warranty. Ballasted systems will still involve these stakeholders, but to a lesser degree.
  • Higher tilt. If the building owner is looking for discretion, attached racking systems can often have a higher tilt, and therefore, a higher visibility to the street.

When considering a rooftop solar system, building owners rely on their solar installation partner to help navigate the many assessment factors to help choose the right racking system.  This is why it is critical to select a trusted partner with demonstrated experience. REC Solar has over 10,000 installations and has worked with all types of commercial and industrial roofs and solar racking systems. Our experienced structural engineers and solar designers will help you choose the right system for your roof.

Contact us for more specific questions about your roof.

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