What Actually Touches Your Roof
Most residential solar installations use a racking system bolted through the roof deck into the rafters below, with each mounting point covered by a flashing flange designed to shed water around the penetration the same way a roof vent or skylight flashing does. The panels themselves sit above the roof surface and don't touch it directly. The mounting feet, and how well each one is flashed and sealed, determine whether the roof stays watertight at that spot for the life of the installation.
Solar on a Flat TPO Roof
On a flat TPO roof, panels go on with either ballasted racking, which sits on the roof and is held down by weight, or attached racking, which is fastened through the roof on flashed mounts. Either one can stay dry if it's detailed to the membrane manufacturer's requirements. Leaks and warranty fights usually start where those details got skipped.
- Ballasted racking doesn't puncture the membrane, but it adds weight and rests right on it. Carlisle recommends a protection layer such as walkway pads under the racking, and GAF's solar guidelines for its guaranteed roofs require sacrificial slip sheets wherever racking touches the roof. Carlisle also points out that large ballasted arrays can block drainage and make the roof hard to inspect.
- Attached racking uses mounts that pass through the membrane into the structure, and every one has to be flashed. Carlisle doesn't recommend relying on adhesive or heat welding alone to attach systems to its membranes, and it prefers mechanically fastened mounts with flashings that fall under the roof warranty. Ask for the manufacturer's approved TPO flashing boots or mounts, not generic ones.
- Roof load. Have a structural engineer confirm the roof can carry the array and any ballast. GAF says plainly that structural review isn't its job.
- Drains. Keep racking clear of drains, scuppers and canales. GAF's guidelines keep projections at least 2 feet from drainage areas next to drains, scuppers and gutters.
- Who holds the warranty. The roof manufacturer warrants the roof, not the solar system; GAF states its guarantees don't cover the PV system. GAF wants the array registered and approved before it goes on, and Carlisle asks owners to notify it and schedule an inspection. The solar installer's warranty covers its own work, so get both parties' terms in writing.
If your TPO roof has some age on it, a Free Roof Report before the array goes on tells you whether it'll outlast the panels.
Why Warranty Language Gets Complicated
Manufacturer roofing warranties typically cover material defects and, in some cases, workmanship. They generally don't cover damage caused by a third party altering the roof after the original installation. If a solar installer's mounting penetration is done poorly and causes a leak, that's a solar-installation problem, not a defect in the original roofing material, and untangling which warranty (if either) applies can get complicated after the fact. The cleanest way to avoid the question is making sure penetrations are done correctly the first time.
Roofing Trade vs. Solar Trade
Solar installation and roofing are two different trades with different core expertise. Many solar companies handle their own mounting and flashing carefully. Still, flashing a penetration correctly for New Mexico's UV exposure and thermal cycling (the same forces that stress every other seal on a roof, covered in our thermal cycling article) is roofing-specific knowledge. It's reasonable to ask directly who is physically doing the roof penetration work and what flashing method they're using.
Timing Matters More Than People Expect
If a roof is anywhere near the end of its useful life, that's worth addressing before solar goes on, not after. Removing and reinstalling a full solar array to replace the roof underneath it later costs significantly more than sequencing the work in the right order: new roof first, solar mounted onto a roof with its full remaining lifespan ahead of it.
What This Means Practically for Homeowners
- Ask who does the roof penetration work, not just who sells and installs the panels. It's a fair, specific question before signing a solar contract.
- Get your roof's remaining lifespan assessed before installing solar, not after, if there's any doubt about its condition.
- Keep documentation of exactly how and where penetrations were made, since that's the information a roofer needs if a leak ever traces back to a mounting point.