It’s a bright idea (cue the duh dum chh drums). But the majority of people who are looking to install rooftop solar are too focused on the PV panels themselves. We want to talk about what's under them.
Rooftop solar is usually presented as an energy decision, and it is one. But before that, it's a roofing decision. A solar array is a long-term commitment bolted or ballasted to an asset that has its own service life, its own warranty, and its own maintenance needs. Get the roofing side of the decision right and the energy side takes care of itself. Get it wrong and you'll eventually pay to install your solar twice.
Two Clocks
A solar array is built around a long horizon. Module performance warranties commonly run around 25 years, and the payback math that leads to a strong financial case for the investment is based on the assumption that it sits there producing for most of that time.
A low-slope roof runs on its own clock. Depending on the system, climate, installation workmanship, and routine maintenance care, a membrane roof might deliver somewhere in the range of 15 to 40 serviceable years.
The issue lies in that the solar array’s clock and the roof assembly’s clock are rarely synchronized. Say you’ve got a 10 year old roof, and you install a solar array that is designed for 25. Somewhere in the next decade, you’re paying a crew to de-energize the system, detach it and haul it off, replace the roof under, and then put it all back on top and re-commission it. You lose production for the duration of the project. You pay for the array installation labor twice. You mobilize equipment and access twice. This is the install-your-solar-twice scenario we mentioned at the start of this article and it is avoidable.
The fix is order of operations. When solar is still a thought bouncing around in your brain (read: you haven’t yet reached out to get a PV system quote), get the roof assessed. If the roof is early in its life and in fair condition, proceed with assessing your options. If it’s mid-life or later, or in poor condition, replace or re-cover it and treat that project as an opportunity to spec up and include solar in one push.
How It Attaches Says A Lot
Once the timelines are aligned, the next question is how the array meets the roof. This is where reasonable-sounding instinct tends to steer projects wrong. There are two primary solar attachment methods: ballasted systems and raised solar systems attached directly to the building’s superstructure.
Ballasted systems are arrays held down by weights instead of fasteners, and they carry a reputation as the least risky choice. That reasoning has surface logic to it: penetrations are potential locations for water infiltration, so a system with no fasteners or penetrations through the membrane must be the safer bet. There’s also a familiar path that leads to ballasted by default rather than decision. Solar shows up in a lot of capital projects as an add alternate; “if there’s money left at the end, maybe we add PV.” Fair enough – but if the money does work itself out at the end, the roof is already designed and detailed (possibly already built), and there’s no going back to integrate anything with the roof system or superstructure. At that point, ballasted isn’t the attachment method that was intentionally chosen but it’s the only door still open.
Measured over the life of the roof, however, ballasted actually tends to carry more risk, not less. The weight of the system bears directly on the roof membrane for decades, and the trays and hardware move – both thermally and in wind events – which creates daily wear and friction with the membrane or slip sheet. Adding on top of that, the system attachment points may interrupt drainage paths and invite ponding water. And when you have those conditions, what you’d really hate to also have – but do – is an effectively unserviceable roof. You can’t inspect what you can’t see, and you can’t repair what you’d have to disassemble a whole array to reach. Distributed risk you can’t see or service is a problem you get to solve forever.
A raised solar system flips that math. Elevate the array on an engineered structural frame that carries the load down to the building’s structure, with the racking held at least a foot or more above the roof surface, and the risks change category. You don’t have weight or friction on the membrane, no trays damming drainage paths, and the roof remains walkable and serviceable for future maintenance or repair needs. Yes, the supports penetrate the roof. But a small number of engineered – preferably circular – penetrations, detailed to be integrated in a watertight manner with the new roof assembly being installed, is a problem you can solve once in design.
The catch is that a raised solar system can’t be improvised at the end of a project. The structure has to be sized for the load, penetrations located and detailed, access planned…the coordination list goes on. The industry talks about design-for-deconstruction – the philosophy that plans a building for its eventual end-of-life so components can be disassembled and reused – and the same mindset can be pointed at operations. Design for maintenance and the risks you know are coming. If rooftop solar is even a possibility, it should be in the design conversation from day one (or as early on as possible). If you have an old roof you’re not ready to replace, but want solar now, a raised solar system really is your best option.
Life After Installation
Once the array is installed and commissioned, the roof’s maintenance program should account for it. How that looks depends on the attachment decision. On a ballasted roof, the plan works around limited access; inspections take longer and see less. In particular, drainage paths and membrane conditions need regular attention. On a raised system, maintenance stays closer to routine. The field of the roof is still walkable and visible, so the inspections look the way they did P.S. (pre-solar) with one minor addition: reviewing the elevated racking penetration flashings for any visual deficiencies like holes, tears, or debonding.
Regardless of the attachment mechanism, your roof is about to see a lot more traffic. On top of the typical facilities and maintenance folks you typically have walking around for roof maintenance, you’ll also have individuals engaged to maintain the solar system. This makes the need for rooftop walkpads even greater than usual, and planning an appropriate access path for where you expect roof traffic based on array layout and access points.
Coordination of O&M contracts and warranties also play vital to your long-term peace. For O&M contracts, the solar provider maintains the array, but a responsible party needs to be clearly defined for the roof system as well. The two scopes should be coordinated and reference each other so that a panel swap down the road doesn’t lead to gray area. In this same vein, check with the roofing manufacturer regarding warranty language and get amendments in writing to acknowledge water intrusion ownership once the panels are up. A leak under an array is awkward to adjudicate between a solar installer and a roofing contractor, and it’s best you not be the one to fund that debate.
Still A Bright Idea
Rooftop solar and a commercial roof can be a great pairing for a long-term owner when considered as the inter-related systems they are. If solar is on your capital plan, put the roof on the agenda first, or install a raised solar system you can roof under later without needing to rely on finding the smallest installer available later. Align the clocks, choose the attachment method with purpose – and early enough to maintain an actual choice in the matter, and develop plans to access and maintain the roof once solar is installed, and it’s a much brighter idea.