The cheapest day to fix a roof under a solar array is the day before the array goes on. After that, every repair is a removal job. Panels come off, racking comes up, the membrane gets worked on, and the array goes back. That is a line item with a crew, a crane in some cases and an electrician, and it is the part of the budget owners forget to carry. In Coeur d'Alene, ID the roof also has to carry a 60 psf ground snow load from the City design sheet, so the roof is working before any panel arrives.
We prepare roofs for arrays and work around the ones already up. Either way, the roof has to outlast the equipment.
The Call: Roof First or Array First
If the membrane has more than a few years left, the array can go on and the roof can wait. If it has less than the array's expected life, the roof goes first. It is that simple, and it is the one question we ask before any layout is drawn. A roof that needs replacement in six years is a bad host for equipment meant to run for twenty-five.
We check the roof the way we would for a replacement: an infrared scan, core cuts and a walk of the seams and flashings. If the answer is a new roof, the cheapest time is now, and the new roof can be designed around the array, with reinforced zones, pads and conduit paths already in the plan.
What the Code Sheet Says: Load Is the First Question
An array adds weight, and it changes where snow collects. Under the 2018 International Building Code that Idaho enforces, a structural engineer has to confirm the roof framing can carry the array plus the snow that drifts against and between the rows. Saturated snow runs about 20 pounds per cubic foot, per the City guidance, which is why the same depth of snow can load a roof very differently from one storm to the next.
The engineer owns that check. We own what the check changes on the roof: where a ballasted array calls for protection board under the blocks, where an attached system needs flashed penetrations, and where the deck needs reinforcement before anything is set.
Mounting: Ballast, Attachment or a Hybrid
Three methods put an array on a flat roof. Ballasted racking sits on the membrane under the weight of concrete blocks, which adds load and avoids penetrations. Attached racking is fastened through the roof, which adds flashing at every post. A hybrid uses a mix. Each choice has a roof consequence.
Ballast needs a protection layer so the blocks do not grind a TPO or PVC sheet, and the roof must be able to carry the added weight on top of the snow. Attachment needs a sealed, flashed detail at every post, and each one is a place for water to enter if the sealant fails. We price the roof-side work for each method so the owner and the solar installer can compare the real total, not just the racking.
Pathways deserve a line. Fire access rules generally ask for clear walkways and setbacks from roof edges and ridges, and the same paths serve the roofer. We mark them with walkway pads so service crews do not wander over the membrane between rows. A path that is drawn on the plan but not protected on the roof turns into a worn trail within two seasons, and the worn spot becomes the first repair.
Conduit is the other quiet cost. Every run from the array to the inverter crosses the roof somewhere, and each crossing is a penetration or a raised support. We route conduit on supports that spread the load, keep runs away from drains and low spots, and seal every entry with a detail that matches the membrane. Ask the electrical contractor where the runs cross before the roof is bid, and the roof scope will match the field.
What It Costs: Prep, Protection and Reset
Four lines carry the money. Roof prep, meaning repairs, new flashing and a clean substrate. Protection, meaning walkway pads, protection board and a clear service path around the array. Structural reinforcement, if the engineer calls for it. And detach-and-reset, the cost of lifting the array later for roof work. Of the four, detach-and-reset surprises owners most, because it comes due years after the install.
We write it into the bid as an alternate with a unit price per panel row, so an owner with an existing array can see what future roof work will cost. If a change order is coming, the trigger is stated in the bid, not argued on the roof.
Timing affects price. Roof work done in the shoulder seasons, before the array season starts, avoids paying for crane and crew time twice. If both trades can overlap, the roof crew finishes ahead of the racking crew by a day or two, and the membrane is protected before the first block lands. We coordinate with the solar installer's schedule when the owner passes it to us, and we stage so that one trade is never standing on the other's unfinished work.
Snow Behavior: Slide, Drift and Edge Loads
A smooth panel surface sheds snow in a rush. Where the panels face a lower roof, an entrance or a parking area, the slide can bury a drain, bend a gutter or hit someone. We look at what sits below the array and recommend snow guards or setbacks where the slide has no safe place to land. Between rows, drift pockets build, and a roof drain nearby has to stay clear.
Edges matter too. The windstorm of November 17, 2015 knocked out power to about 238,000 customers across the Spokane and North Idaho region, a reminder that perimeter fastening and edge metal on a roof with an array are worth pricing carefully. A loose edge near racking is a problem for the roof and the equipment.
Where It Shows Up: Buildings with the Roof Area
Large, low roofs with few obstructions suit arrays best. Tilt-up warehouses and flex buildings at Riverbend Commerce Park in Post Falls are the kind of low-slope shell that suits an array. On any of them, the roof plan has to account for the equipment, hatches and drains already up there.
When the roof has to go first, a commercial roof replacement finishes the membrane before the racking crew arrives. Where the existing roof can stay, a recover sets a fresh membrane under the array.
Commercial Roofing Questions
Do we need a new roof before we install solar?
Only if the roof will not outlive the array. We test the roof and give the remaining life in plain numbers. If it is short, replace first.
Can an existing array stay in place during roof repairs?
Small repairs at the edges can be done around it. Anything under the panels means detach and reset. We price both so the owner sees the difference.
Does solar void the roof warranty?
It can, if the mounting breaks the manufacturer's rules. We follow the membrane maker's details for the mounting method and keep the records. Send the warranty before the layout is final.
Who flashes the posts on an attached array?
It should be the roofer or someone working to the roofer's details. We can flash the posts or supply the detail and inspect the result. Split responsibility is where leaks start.
What does snow do to a solar array on a flat roof?
It slides, drifts and loads the framing. The engineer checks the load. We check the slide path and the drains, and we add snow guards or setbacks where needed.