A solar array is a 25-year decision. The roof under it may not be.
When those timelines don’t align, the array comes off and goes back on partway through its life, and you pay labor twice for work that produces no additional energy. It is the most avoidable cost in residential solar, and it is almost always locked in at the moment somebody signs a contract without a straight answer about the roof.
This post is about that one decision: how many years your roof has left, how to find out before you sign, and the specific situations where installing over an older roof is still the right call. At Sunlight Electri-Cal Solutions, we handle both trades, so we have no reason to tell you the roof is fine when it isn’t, and no reason to sell you a roof you don’t need.
The short answer
Do the subtraction before you sign:
- How many years does the covering have left, on the planes the array will actually occupy?
- How many years do you expect to own the home?
- If the roof runs out first, reroof before the array goes up, unless one of the specific exceptions below applies.
The threshold is not a fixed number of years. It is whether the roof will outlast your ownership, and whether you would rather pay for a reroof now or pay for a reroof plus a removal and reinstall later.
Why the timing matters more than the roof
The reason this decision carries weight is an asymmetry most homeowners do not see until it is too late.
If the roof is replaced before the array goes up, the roofing crew works on a clear roof, every attachment and flashing is set into new material, and the deck under every future mounting point gets inspected while it is exposed.
If the roof is replaced after, the array must be removed, stored, and reinstalled, with electrical disconnection and recommissioning on both ends. That work is real labor, and it generates nothing new. It is purely the cost of having done things in the wrong order.
One thing worth settling, because homeowners often worry about the wrong risk: a removal and reinstall that returns the same equipment to the same roof does not increase your system’s nameplate capacity. PG&E’s net metering schedules key their modification thresholds to increases in a generating facility’s generating capacity, so a like-for-like reinstall is a different event from expanding a system. Your exposure in a reroof-under-array project is labor and scheduling, not your tariff.
Step one: find out how old the roof actually is
Before anyone climbs anything, spend an afternoon on documents. This is free, and it frequently settles the question outright.
Three sources are worth chasing, in this order:
- Your city or county building department’s permit records for your address. A reroof permit tells you when the covering was replaced and often what went on. Most homeowners never think to ask, and it is the single most useful document available.
- The seller’s disclosure statement from when you bought, which may state the roof’s age and disclose prior leaks or repairs.
- The home inspection report from your purchase, which usually contains a roof section. Note its date, because that assessment has aged alongside the roof.
If none of them answer it, that is a finding in itself. It means the decision rests entirely on condition, which raises the value of getting a proper written assessment before you commit to a solar contract rather than after.
Step two: understand what service life figures can and cannot tell you
Published service life ranges are a starting point for the subtraction, not an answer.
The Asphalt Roofing Manufacturers Association offers the most commonly used benchmark for asphalt: a residential roof over 20 years old is, in its words, “a prime candidate for reroofing.” ARMA publishes no numeric service life for three-tab or laminated shingles specifically.
InterNACHI, the home inspectors’ association, publishes a widely cited life expectancy chart that puts three-tab asphalt shingles at 20 years and architectural asphalt at 30, with clay and concrete tile at 100 or more. InterNACHI is careful about how those should be read, describing them as guidelines only and stating that “the life of a roof depends on local weather conditions, building and design, material quality, and adequate maintenance.”
Take that caveat seriously, because the factors it names vary house to house in ways that matter here:
- Which plane you are looking at. South- and west-facing slopes take far more sun exposure than north-facing ones, and the array usually goes on the more exposed side. The relevant number is the remaining life of the array planes, not of the roof as a whole.
- Attic ventilation, which determines how hot the underside of the deck runs.
- Installation quality, particularly at flashings and edges, which decides whether a covering reaches its intended life or fails early.
- Whether the roof already carries more than one layer.
A tile roof deserves a specific warning here, because the headline number misleads. The tile itself can last generations. The underlayment beneath it, the flashings, and the deck cannot, and those are what actually fail. A tile roof can need significant work while nearly all of the tile remains perfectly serviceable, so “it is tile, it will outlast the panels” is not a safe assumption.
Step three: get the assessment in writing before the solar contract
This is the step that prevents the expensive outcome, and the sequence is the whole point. Get the roof assessed before the solar contract is signed, not as a change order afterward.
For a solar decision specifically, the assessment needs to answer four things:
- Remaining service life, plane by plane, with the array planes called out separately rather than one verdict for the whole roof.
- The number of layers present, because that changes both the re-roof cost and what is possible.
- Deck condition wherever it could be observed, and an explicit note of where it could not.
- Any area of active or prior water intrusion.
Get it in writing with photographs and a date. A verbal “your roof looks fine” is worth nothing in year seven, and a dated written assessment turns out to be useful well beyond this decision.
Step four: the one technical reason tear-off beats a layover under solar
If the answer is that the roof needs doing, there is a solar-specific reason to tear off rather than lay new covering over old, and it is not obvious.
California publishes structural criteria that let a residential rooftop PV project qualify for simplified review without project-specific engineering. One of the qualifying questions asks whether the roof is “a single roof without a reroof overlay.” Another asks whether the structure appears sound “without signs of alterations or significant structural deterioration or sagging.”
So a layover can push your solar project out of simplified review and into territory where drawings and calculations must be, in the Guidebook’s words, “stamped and signed by a California-licensed civil or structural engineer.” That is a cost and a delay you would be buying in exchange for skipping a tear-off.
There is a second reason, which is simply that a reroof is the only moment in the roof’s life when the deck under every future mounting point is visible. Covering it over wastes that opportunity for nothing.
When installing over an older roof is still reasonable
A blanket “always reroof first” is oversold, and there are real situations where putting the array on an older roof is the right call. Four of them come up repeatedly:
The array planes were already redone. Roofs get replaced in sections. If the plane carrying the array was recently recovered and you can document it, the age of the rest of the roof is not the array’s problem.
The array is not going on the aging plane. If the design puts modules on a sound plane and the worn area is elsewhere, the two decisions can be separated. This is worth raising with your installer at the design stage, because layout is often more flexible than a first proposal suggests. Our solar system design guide for Bay Area homes covers how plane selection works.
A low-slope section is on its own schedule. Low-slope areas are frequently a different system from the sloped field, and on the roofs we work on that usually means a TPO or modified bitumen area alongside a composition shingle field. Those can be addressed independently.
You are selling within a few years. If the array will not outlive your ownership by much, the reroof timing question largely becomes the next owner’s. Pretending otherwise just moves money around, though it does become a disclosure and documentation question at sale.
A fifth option sits between the two: recover only the planes the array will occupy and leave the rest on its own timeline. This works where planes are genuinely in different condition. The thing to scrutinise is how the new-to-existing transition will be flashed, so ask about that detail specifically.
What to settle in the contract before you sign
Whatever you decide, put the roof question in writing rather than leaving it as a shared assumption:
- What is the stated remaining roof life that this proposal assumes, and who assessed it?
- If the roof needs replacing within the system’s life, who removes and reinstalls the array, and at what cost? Get a figure or a formula now, when you have leverage, rather than in year eight.
- What is the attachment method and the flashing detail at each penetration?
- Whose workmanship warranty covers the roof penetrations, and for how long?
- If a leak appears near the array, who is responsible for diagnosing it, and who pays if the cause is disputed?
That last question is the one that separates a well-run project from a bad one, and it is much easier to answer when the roofing and the solar sit with the same company. Our roofing services cover both sides of that for exactly this reason.
What this post is not about
Three things deliberately left out, because they are separate decisions:
- Panel, racking, and mounting hardware selection. Covered in comparing different types of solar panels.
- The logistics of a removal and reinstall project. That is its own subject and gets its own post.
- Whether solar still pencils out at all in 2026, which changed substantially this year and is covered in what Bay Area homeowners actually get for solar.
For the rest of the pre-installation checklist, our guide to preparing your home for solar installation covers what else to sort out beforehand.
Frequently asked questions
There is no single age. The question is how many years the covering has left on the planes the array will occupy, measured against how long you expect to own the home. ARMA treats a residential asphalt roof over 20 years old as a prime candidate for reroofing, and InterNACHI’s chart gives 20 years for three-tab and 30 for architectural asphalt as guidelines, but condition and documentation decide it rather than age alone.
Replace first if the array planes will run out of service life before you expect to sell, if you cannot document the covering’s age and its condition is ambiguous, or if an assessment finds deck problems or water intrusion. Install over the existing roof if the array panels are documented as recently replaced, if the array is going on a sound plane while the worn area is elsewhere, or if you are selling soon.
It varies by module count, roof complexity and height, racking type, and what the deck looks like once the covering is off, so get a figure in writing in the contract rather than a verbal estimate. The point of this post is that the cost is avoidable: it exists only because the roof and the array were done in the wrong order.
No. A like-for-like removal and reinstall does not increase your system’s generating capacity, and PG&E’s net metering schedules tie their modification thresholds to capacity increases. Your exposure in a reroof-under-array project is labor and scheduling, not your tariff.
You can, and sometimes that is correct, but do it with the numbers in front of you rather than by default. Price the reroof now, and the reroof-plus-removal-and-reinstall later, and compare. If the gap is small and the roof has a decade left, installing now is defensible. If the roof has five years left, it rarely is.
Not necessarily. The tile itself is extremely long-lived, but the underlayment, flashings, and deck beneath it are not, and those are what fail. Ask specifically about the underlayment’s age and condition, not just the tile.
Someone qualified to assess roofing, and you should get it in writing. Where the roofing and solar sit with the same company, the assessment and the install are coordinated by default, but whoever you use, ask for a plan-by-plan written assessment with photographs rather than a verbal opinion.
Getting a straight answer before you commit
We will tell you when your roof does not need replacing. That answer costs us the roofing job, and we give it regularly, because putting an array on a sound roof and coming back in twelve years is a better outcome than selling work that was not needed.
If you want your roof assessed plane by plane, in writing, before you sign a solar contract, contact our team. Bring whatever documentation you found, including permit records and your original home inspection report, because it genuinely shortens the conversation.
A note on sources: service life figures are from InterNACHI’s Standard Estimated Life Expectancy Chart for Homes and from the Asphalt Roofing Manufacturers Association, both cited above and both published as guidelines rather than guarantees. Structural prequalification criteria are from the California Solar Permitting Guidebook, 4th Edition. Tariff statements reflect PG&E’s net metering schedules as published in October 2026. PG&E revises its tariffs regularly, so confirm current terms before relying on them.
Sunlight Electri-Cal Solutions serves Dublin, the Tri-Valley, and the greater Bay Area. Roofing by Sunlight Roofing Inc., CSLB #1158264. Solar and electrical by Sunlight Electri-Cal Solutions, CSLB #1055220. Every roof replacement we perform includes a 10-year workmanship warranty.
