Is Your Commercial Rooftop Ready for Solar?

Is Your Commercial Rooftop Ready for Solar?

A Deep Dive into Roof Readiness for Commercial/Industrial Facilities

At Pisgah Energy, we regularly work with Facilities Managers to confirm that their rooftops are solar-ready. In this blog, based on my 3 part LinkedIn miniseries, we’ll explore three major rooftop considerations to address before greenlighting a solar project.

Quick Takeaways

Part One: Structural Engineering – addresses the necessity of having a structural engineer determine if your rooftop can support a solar installation

• Part Two: Roof Readiness – Metal Vs. Membrane – addresses how the age and type of roofing material relate to the solar readiness of your facility

• Part Three: Ensuring Roof Warranties Remain Intact – addresses what we do to ensure our clients’ roof warranties remain intact during project development


Part One: Structural Engineering

image of calipers on plans

In terms of sequencing due diligence, having a structural engineer assess your rooftop is the first order of business. After all, if a structure can’t hold the weight of a proposed solar installation, the project is a no-go from the get-go.

Let’s dig a little deeper.

Solar rooftop racking systems and their attachment methods are designed based on a specific region’s wind speeds and snow loading requirements. Therefore, careful consideration must be given to the structures that will support these systems for the next 30+ years.

It’s critical then to have a licensed structural engineer assess the rooftop framing for the given region’s dead and live loading requirements.

What does that look like in practice?

When we design projects in Western North Carolina, the systems are engineered for a 115-mph wind zone and typically weigh 3-5 lbs. per sqft. Designing projects in the Outer Banks is a different story. These systems are engineered for wind speeds of 140 mph + and can weigh in excess of 20 lbs. per sqft. Compare these two scenarios, and it’s clear that the weight of a solar installation is inextricably tied to the region in which it is built.

Consequently, it’s the designer’s job to determine the regional wind speed/snow loading requirements. This crucial information allows them to design a system that won’t blow off the roof at the first hint of hurricane season. Once designed, it’s the structural engineer’s job to assess whether a facility’s rooftop framing can hold the weight of the proposed solar project. In addition, it’s our job to ‘eyeball’ the soundness of a roof’s structure on the initial site visit. We flag any major issues, like rotting timbers or an abundance of equipment hanging from the roof’s framing, so they can be dealt with ahead of time.

Bearing the Load

Once the structural engineer has finished their assessment, they provide a letter certifying that the rooftop’s framing structure can accommodate the extra weight. That letter is then used as proof to the facility owner that their roof framing system is viable for solar. The permit office also gets a copy as they require evidence of a completed assessment prior to issuing any permits.

Once your rooftop framing is determined to be ‘good to go, it’s time to look at roof readiness.

Part Two: Roof Readiness – Metal vs. Membrane

So, you’ve determined that your roof is structurally sound and can support solar. Now it’s time to examine its age and type of roofing material. Some rooftops are clearly in need of replacement, while others have many years left. How, then, do you know if you should replace your rooftop before adding solar?

Consider this: The expected life of a solar installation is 25-30 years. Now compare that to the current age of your rooftop. Are those two numbers in relative alignment?

When exploring the use of solar at your facility, it’s important to weigh the expected life of your rooftop against the expected life of the solar system. This will help determine if your rooftop needs replacing prior to the installation of a solar system. Generally, if your rooftop is due to be replaced in the next five to ten years, we recommend an early replacement. This allows you to avoid the cost of doing a solar removal and remount (R&R) in five years when it’s time for a new roof.


Commercial rooftop solar array lwh Pisgah Energy Asheville NC

I have a rooftop that’s 11 years old and has a 20-year warranty. I’ve decided I want to ‘go solar’. Do I replace the roof now? Do I wait until the warranty runs out? It’s important for me to look at the cost of doing both so I can make a choice with clear eyes. I certainly don’t want to be surprised by the expense of a solar R&R down the line. And neither do you.

When considering solar, it’s also important to note that all rooftop ages are not created equal. If you have a 20-year-old standing seam roof, it may have 20+ years of life left, while a 20-year-old membrane may need to be replaced today. In other words, the age AND type of roof should be examined closely when preparing to install a solar system.


Roofing Material + Solar Modules

Okay, so you know you’re going to install a solar system and you’ve decided to replace your rooftop first. Now what? While you’re likely to replace your rooftop with the same material, it’s a good idea to understand how it works in conjunction with the solar modules. Regardless of what’s used, there are choices you can make to ensure that your rooftop is in the best possible position to support solar.

Let’s take a closer look.

Disclaimer: The roofing materials discussed below are what we have encountered the most in the southeast. This is certainly not an exhaustive list, nor are we a roofing contractor. Be sure to consult a professional roofing contractor when determining what type of roofing material will best suit your facility’s needs and budgets.


Corrugated metal rooftops are a low-cost option and can last 20 – 30 years. However, putting solar on a corrugated rooftop requires penetrating metal that has already been heavily drilled. Not only do these new penetrations further weaken the rooftop, but they can add to the material and labor costs of a solar project. Why? Because attachment points for the racking system need to be physically installed on the metal ribs and sealant must be used to prevent leaks.

Standing seam offers the longest life of any rooftop – lasting up to 50 years. They are more expensive than corrugated, but can last twice as long and typically come with a weatherization warranty. The relationship between standing seam and solar is less fraught as well. Solar racking can be clamped directly onto the seam – no penetrations or sealing required. Because of this, the project requires less labor and less materials so costs and install time go down. Overall, having a standing seam rooftop results in the most cost-effective solar installation.


In our experience, TPO rooftops are the most used membrane for commercial/industrial facilities. TPO membranes are low-cost, durable, recyclable and energy efficient. However, because it’s a relatively new technology, TPO is not as time-tested as it’s PVC counterpart.

As mentioned above, PVC membranes have been around longer and have a more proven track record. They are also energy efficient, tend to last longer than TPO and have a strong chemical resistance. However, PVC is more expensive and not as environmentally friendly.

Solar mounted on either a TPO or PVC membrane would use a ballasted racking system – no penetrations required.

The warranty length for any rooftop membrane directly relates to its thickness.

45 mil = 15-year warranty
60 mil = 20-year roof warranty
80 mil = 30-year warranty

Think 30 Years Ahead

If you’re looking for a roofing system that’s going to last the longest, perhaps as long as your solar system, go with the 80-mil thickness and get that 30-year warranty. If selecting the 45-mil or 60-mil membrane, be prepared to face a solar R&R down the line.

Keep in mind: The higher upfront cost of an 80-mil membrane will be much less than the cost of doing that R&R at year 20 or 25.

When in Doubt…

If uncertain about the useful life of your rooftop, it may be beneficial to get the professional opinion of 2-3 roofing contractors so you know where you and your rooftop stand. Too covered up to take on this task? A good solar developer can assist by contacting the roofing pros and bringing them on-site to make an assessment.

Part Three: Ensure Roof Warranties Remain Intact

Alright, we’re in the final stretch here. Your roof structure is solid and the rooftop material is solar-ready with a long life ahead of it. Now, what about keeping the roof warranty intact?

Part of our job as a solar developer is to make sure that the installation requirements of the chosen solar racking system meet the roof manufacturer’s requirements for the warranty to remain intact.

image of solar installer working on a rooftop solar panel

To determine the compatibility of the racking and roofing we must ask:

Who is the roofing manufacturer?

What warranty, if any, is in place?

These questions allow us to confirm with the roofing manufacturer their requirements for rooftop overburden protection and any other relevant requirements for keeping the warranty intact.

Once we know the roof manufacturer, we put in a request for their overburden protection forms. We use these forms to document how the solar system will be installed – including the technical specifications of the equipment being used. With this documentation in hand, the roofing manufacturer has all the information necessary to determine that the proposed solar system meets their warranty requirements. It’s critical that all of this work is done prior to installing the solar project – we want to avoid doing anything that might void the warranty.


Fast forward to the successful installation of your rooftop solar project – congratulations! Now it’s time for the roof manufacturer’s inspection. (Some manufacturers require an inspection prior to a solar installation, but most will wait until the project is complete. It all depends on the manufacturer.) Upon completing the inspection, the manufacturer will sign off on the warranty. If, on the off chance there is an issue with the installation, the roof manufacturer will recommend a remedy.

What if there is no warranty on the roof?

Warranty or no, it’s our job to take the same care and perform the same due diligence. The only difference is there won’t be an inspection upon project completion.

Keep in mind:

  1. Corrugated rooftops do not come with a warranty.
  2. If you have TPO/PVC, a warranty-less roof most likely indicates an expired membrane.

Protect Your Membrane

Speaking of membranes, due to thermal expansion ballasted solar systems will move slightly relative to the roof surface. Because of this, roofing manufacturers often require a protective surface be placed between the racking and the membrane. Most often, a slip sheet barrier is created using a piece of the membrane itself, however, a lot of racking systems now have built-in padding. This kind of padding will work as long as it meets the roof manufacturer’s requirements.

What about Leaks?

We understand that leaks are a major concern for facilities managers and with good reason. It’s important to understand, however, that if the solar system is installed based on the specifications and requirements of the roofing manufacturer, the chance of any leakage is incredibly small.

We’re Here to Help.

As you can see, a lot goes into making sure your rooftop is solar-ready, but you don’t have to go it alone. A professional solar developer can help you every step of the way.

That’s what Pisgah Energy is here to do – guide our clients’ solar projects, from concept through construction.