Getting the Roof Ready Before the Array
The roof should outlive the panels, or at least not fall due for replacement a few years after they go on, because removing and resetting an array to reroof under it is a large extra cost. Before a solar contractor starts, we survey the roof for wet insulation with an infrared moisture survey and cut cores where the scan shows heat retention. If the roof is near the end of its service life, the conversation changes to replacement first and solar second, and we say so while the schedule can still adjust.
Where the roof is sound, preparation means finishing the details that panels will lean on. Drains are cleared and given their own protection, ponding areas are corrected with tapered insulation, and the membrane gets reinforcement or walkway pads along the routes the installers will use. We mark the zones where mounts will go and set curbs or flashed bases in place ahead of time when the structural engineer calls for it. Loads are the engineer's decision, and the roof surface is ours to make ready.
Standing Seam, Single-Ply and Coated Roofs Under Panels
Different roofs take an array differently. A standing seam metal roof can usually accept clamps that grip the seam without piercing the panel, which avoids new holes altogether, though the clamp has to suit the seam profile and the finish must survive the pressure. A single-ply sheet such as TPO needs mounts on flashed bases or pedestals, with the membrane welded up each post and a sealed termination at the top. An older built-up or modified bitumen roof needs the surface checked for blisters and loose laps first.
Coated roofs need a compatibility check. A coating that is not meant to be walked on will scuff under installer traffic, and a pedestal set into a worn coating will not bond well. Sheet metal around the array gets the same detail work as anywhere else: counterflashing set properly into its reglet, cap metal formed and lapped, and every sealant joint tooled where we can inspect it later.
Class A Assemblies, Wind and Heat Under the Panels
Foothill roofs face a fire question that comes before any solar question. In Pasadena, the Arroyo Seco and upper Hastings Ranch hold mapped fire hazard zones, and properties in the Very High zone must use a Class A covering for new construction and for any reroof that replaces over half the roof within twelve months, with the rating judged on covering, underlayment and deck together. A reroof done ahead of an array has to meet that rule, and mounts and wiring should not disturb it. The Eaton Fire began on January 7, 2025, with Santa Ana gusts forecast at 60 to 80 mph and isolated gusts up to 100 mph, a wind and ember exposure that mounts, wiring and edge metal in the foothills must handle.
Heat and wind both change under panels. The roof beneath an array runs cooler than an open roof in the afternoon, but it also holds heat in the narrow gap beside each row, and wind can pry at a panel edge and lift a nearby membrane. We keep a clear perimeter strip for edge metal and drains, and we confirm that the reflective surface chosen for the roof keeps meeting California's aged values in the places the panels do not cover.
Working Around an Array Already on the Roof
Many buildings now carry panels, and the leak rarely waits for a convenient date. Caltech completed a 1.3 MW array in 2010, a reminder of how long an installation stays on a roof, and any roof beneath an array of that age has been through more than a decade of heat and winter rain. When we find a leak under or near an array, we trace it with the panels in place where possible, and when it cannot be reached we coordinate with the solar contractor to lift only the rows needed and reset them. We do not touch the electrical side. Our job is the water path.
Office buildings along South Lake Avenue compete in a Tri-Cities market that stood at 26.1 percent vacancy in late 2025, and an owner weighing a rooftop array there is weighing it against operating cost and tenant demand. Keeping the manufacturer's records in order, so the panel mounting method and the roof system are both documented, helps with roof warranty management when anyone later asks what was approved and when.
Commercial Roofing Questions
Should the roof be replaced before solar goes on?
Replace first when the roof has less service life than the planned array. We check membrane, insulation moisture, and deck condition before the solar installer fixes the array schedule.
How are mounts attached to a roof without creating leaks?
Each mount rises from a flashed base or pedestal that is welded, adhered or sealed to the membrane as the system requires, with a termination that sheds water instead of relying on sealant alone. Standing seam roofs can often use seam clamps that need no holes.
Can you repair a roof that already has panels on it?
Usually, with the solar contractor lifting and resetting the rows we need access to. We find the leak first, so the number of panels moved is as small as possible. Electrical disconnection and reconnection stay with the licensed solar or electrical trade, and we schedule our work around theirs.
Does an array change the fire rating of the roof?
The roof assembly keeps its own rating, and the installation as a whole is judged by the solar designer and the fire authority. Our part is making sure the covering, underlayment and deck stay a compliant Class A assembly where the zone requires it, and that wiring and mounts do not cut through that assembly carelessly.
Will adding solar affect my roof warranty?
It can, if the mounting method conflicts with the written terms for that roof system. Requirements vary by manufacturer, so we review the warranty and request written approval for the attachment before installation.
