Get Your Roof Solar-Ready Before the Installer Shows Up
Installers price the same panels three different ways depending on what they find on your roof. Do the homework yourself and you walk into every quote knowing what the honest number should be.
A rooftop solar array is a 25-year appliance bolted to a roof that might not last that long. Every installer who quotes you will assess three things before they talk price: how many years the roof has left, how much of it faces the sun without shade, and how easy it is to get wire from the panels to your electrical service. You can answer all three yourself in a weekend for nearly nothing, and doing so changes the conversation from being sold to comparing bids.
Roof age math
A standard architectural asphalt shingle roof lasts 22 to 30 years. Removing and reinstalling an array to replace a roof underneath it costs $3,000 to $6,000, so if your roof has fewer than 12 years left, replace it first and roll the two projects together. Find your roof’s age from the permit record, the last invoice, or the home inspection; if none exist, look for granule loss in the gutters, curled edges, and bald patches. A metal roof changes the equation entirely: it outlives the panels and standing-seam clamps mean no roof penetrations at all.
Map the usable roof
From the ground and a ladder, sketch each roof plane on graph paper with its compass orientation and pitch. Measure the planes that face south, southwest, or southeast; in the northern hemisphere those produce the most electricity, with east and west planes yielding about 15 percent less. Subtract 3 feet of fire-code setback along the ridge and the eave-to-ridge path, and note every vent, chimney, and satellite mount. Each residential panel is about 65 by 40 inches and produces roughly 400 watts, so a clean 300-square-foot south plane holds about 16 panels, or a 6.4-kilowatt array.
Run a shade study
Shade is the array killer, and a single shaded panel can drag down a whole string. Stand at the center of each candidate plane, or as close as you safely can, and photograph the horizon with a sun-path app overlaid, at 9 a.m., noon, 3 p.m., and 5 p.m. Note the trees, the neighbor’s roofline, and your own chimney. Anything that shades the plane between 10 a.m. and 3 p.m. from March to October is a real loss. A tree you own can be trimmed before the installer arrives; a neighbor’s cannot, so plan around it.
Check the structure from the attic
A solar array adds only about 3 pounds per square foot, which almost any code-built roof carries. What matters is the condition: get into the attic with a flashlight and look at the rafters or trusses under your target plane for cracks, water staining, sagging, or notching. Measure rafter size and spacing and photograph it; installers need this for their engineering letter and having it ready saves a site visit. Also note the roof decking type, since 3/8-inch plank or badly delaminated OSB may need reinforcement.
Trace the conduit path
Wire from the array has to reach an inverter and then the main panel. Walk it: from the roof plane down an exterior wall or through the attic, to the panel location. The cleanest path is through the attic to a wall directly above the panel, dropping in the wall cavity. If the panel is on the far side of the house, an exterior conduit run painted to match siding is normal but visible; decide now which wall you can live with. Note the electrical service size on the main breaker, because a 100-amp panel often needs a line-side tap or an upgrade, and that is a $500 to $3,000 line item to ask about.
Size the system from your bills
Add up 12 months of kilowatt-hours from your electric bills. Divide by the local production factor, typically 1,200 to 1,600 kilowatt-hours per installed kilowatt per year depending on how sunny your region is, to get the array size that offsets your usage. If that number is bigger than your roof plane can hold, you know before the quote that you will be offsetting a percentage, not the whole bill. If it is smaller, ask installers about future-proofing for an EV or a heat pump.
Do not walk a roof steeper than 6-in-12, a wet roof, or any roof more than one story up without a harness and someone on the ground. Everything in this checklist except the attic inspection can be done from a ladder at the eave. And do not sign a solar contract that does not include a roof condition clause; if a salesperson tells you a 20-year-old roof is fine, get a roofer’s opinion first.
The panels are a 25-year bet. Make sure the roof under them is in for the same term.
Walking into the quote
With your roof sketch, shade photos, rafter data, bill total, and conduit path on a clipboard, you have done what a good installer’s site surveyor does, and you will spot immediately when a quote sizes the array wrong or ignores a shading problem. Get three bids, ask each for a production estimate in kilowatt-hours per year, and compare cost per watt installed. Reading those quotes line by line is its own skill, and the natural next article.
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