Short answer: taking a solar array off a roof, replacing the roof, and putting the same array back does not, by itself, increase your system's generating capacity — and generating capacity is what the tariff rules actually measure. But nobody at a roofing company gets to make that determination for you. SDG&E does. And there are specific, avoidable ways a reroof project turns into a system change without anyone intending it.

This page explains what your grandfathering is, what the rules literally say, where the real risk sits, and what we do on our end to keep the paperwork boring.

Every tariff statement below carries a link to the source and a last-verified date. Rules change. If you're reading this long after the verification date, check the source before you rely on it.

What NEM 2.0 grandfathering actually is

If your solar was interconnected before April 15, 2023, you're on an older net metering tariff, and California guarantees you a defined run on it.

The CPUC states it plainly: customer-generators "are allowed to remain on the NEM 2.0 tariff for 20 years from the date they interconnected." (Source: CPUC, Net Energy Metering and Net Billing. Last verified August 21, 2026.)

In San Diego, the tariff has a different name than the one everyone says out loud. SDG&E's NEM 2.0 is Schedule NEM-ST — "Net Energy Metering Successor Tariff." SDG&E hit its NEM 1.0 cap on June 29, 2016, and interconnections after that went onto NEM-ST. Its own language: eligible customer-generators may remain on the schedule "for 20 years from the original year of interconnection." (Source: SDG&E Schedule NEM-ST. Last verified August 21, 2026.)

Two things worth noticing. The clock runs from interconnection, not from the day the panels went on the roof and not from the day you signed. And it's tied to the generating facility, not to you personally — which is why the rules care so much about whether that facility has changed.

What replaced it, and why people are nervous

Since April 15, 2023, new interconnection applicants take service on the net billing tariff — NBT, informally "NEM 3.0" — adopted by the CPUC in Decision D.22-12-056. (Sources: CPUC Net Billing Tariff; CPUC, Net Energy Metering and Net Billing. Last verified August 21, 2026.)

The practical difference for a homeowner is what a exported kilowatt-hour is worth. Under net billing, export credits are well below retail rates, which changes the arithmetic of a system that was designed and sold on the assumption that the grid would bank power at something close to retail. That's why "will this cost me my NEM 2.0" is the first question out of people's mouths when we tell them their roof needs replacing. It's a reasonable question. It's also the wrong thing to be afraid of, most of the time — the fear is usually pointed at the roof when it should be pointed at the equipment list.

The actual question: same panels, off and back on

Here's the case we're talking about. Same site. Same modules, the exact ones that came off. Same inverter. Same string layout. Same module count. New underlayment, new roof covering underneath. Nothing about the electrical system changed except that it spent two weeks in your garage.

The tariff test for keeping your transition period is written around capacity, not around whether the roof underneath got replaced. SDG&E: generating facilities eligible for the 20-year transition period "that are modified and/or repaired shall remain eligible for the remainder of their 20-year transition period as long as the modifications and/or repairs do not increase the Generating Facility by more than the greater of (1) 10 percent of the Generating Facility's nameplate rating capacity, as established when the Generating Facility was originally interconnected, or (2) 1 kW." (Source: SDG&E Schedule NEM-ST. Last verified August 21, 2026.)

SDG&E puts the same rule in homeowner language on its NEM page: systems 10 kW and smaller can be increased by no more than 1 kW; systems larger than 10 kW by no more than 10% of existing size. Exceed it, and SDG&E states the customer becomes responsible for non-bypassable charges on 100% of the net kWh delivered. (Source: SDG&E, Net Energy Metering. Last verified August 21, 2026.)

Run the math on your own system. A 6 kW array: the threshold is the greater of 1 kW or 600 W, so 1 kW. A 12 kW array: the greater of 1 kW or 1.2 kW, so 1.2 kW. That is your headroom. A true like-for-like reinstall consumes none of it.

We are not telling you your grandfathering is guaranteed. We can't, and neither can any contractor who tells you otherwise. Eligibility under the tariff is determined by SDG&E, under rules set by the CPUC. What we can do is make sure the project we hand them doesn't give them a reason to look twice.

Where the risk actually lives

Every case we've seen where a homeowner had a real problem, the problem was a system change bundled into a roof project — not the roof project.

"While you're up there, can we add a few panels?"

This is the big one. It is a completely natural thing to ask while an array is already on the ground, and it is the single fastest way to eat your 1 kW of headroom. Adding capacity is a legitimate decision — but it's a separate decision with its own consequences, and it should be made deliberately, with the threshold math in front of you, not as an upsell on reinstall day. If you go past the limit, SDG&E's own tariff says you have the option of metering the additions separately under another eligible tariff, or having the entire generating facility served under another tariff. (Source: SDG&E Schedule NEM-ST. Last verified August 21, 2026.) That second option is the one that hurts.

Broken modules and the wattage creep problem

If a module cracks during removal — it happens, and anyone who says it never happens hasn't done enough of these — you can't usually buy the identical module you bought in 2017. The replacement carries a different nameplate rating, often a higher one. Replace one module, nothing moves. Replace six on a small array and you can walk past 1 kW without anyone writing "system expansion" on a single document. This is why we photograph and log every module by serial before it comes off, and why we tell you before we order a replacement, not after.

Changing the inverter

An aging string inverter is a tempting thing to swap while everything is disconnected. Understand what that is: SDG&E's own interconnection application lists "Physical Changes to an Interconnected NEM or NEM-ST Generating Facility" as its own application type, described as a request for modification of an existing interconnection "due to modifications (e.g., adding photovoltaic ('PV') panels or changing inverters/turbines)" to a facility already operating under an interconnection agreement with permission to operate. (Source: SDG&E NEM Interconnection Application and Agreement, Form 142-02774. Last verified August 21, 2026.) The utility has a form for this. Filing it is not automatically bad. Filing it without knowing you filed it is bad.

Adding a battery

Batteries are usually the right answer in SDG&E territory — peak is 4–9pm, and self-consumption is where the value is now, not export credits. But a storage addition is a change to the interconnected facility and belongs in its own conversation with its own paperwork, not stapled to a roofing invoice. If you want to talk about it, talk about it — see our battery storage page. Just don't let it ride along silently.

The reroof itself

Notice what isn't on this list. New shingles, new tile, new underlayment, new flashing, a fully rebuilt deck — none of that touches the nameplate capacity of your generating facility.

Book a reroof-under-solar assessment — or call (858) 541-1097.

The San Diego permit side, which is its own thing

The City of San Diego addresses this case directly. Where existing roof-mounted PV is removed for renewal of the roof covering, the original approved record plan set must accompany the submitted PV plans to confirm the system was permitted and installed, and a pre-removal inspection of the existing system may be required. The bulletin is explicit that the permit for re-installation of the existing PV "does not allow any alteration of the original equipment or system," and that the PV work for re-roofing purposes "shall be performed by a qualified contractor holding a C-10 or C-46 license." (Source: City of San Diego Information Bulletin 301, rev. May 2026. Last verified August 21, 2026.)

Read that last requirement twice, because it's the whole reason this job goes sideways when it's split between two companies. The roof needs a roofing classification. The panels need an electrical or solar classification. Somebody has to hold both, or you're coordinating two contractors who each think the other one owns the seam — and the seam is where the leak is.

McKay holds both sides of that seam under one license. CSLB license #1130793 is current and active and carries B (General Building), C-10 (Electrical), and C-39 (Roofing) classifications — the roofing work and the PV electrical work run under the same contractor, so there is no seam for a leak or a paperwork gap to hide in.

Note also that the City's bulletin says the reinstallation permit doesn't allow alteration of the original equipment or system — which is a second, independent reason that "while you're up there" changes deserve their own deliberate path rather than being folded into the reroof permit.

What we do to keep the paperwork clean

1. We ask for your interconnection date and your permission-to-operate letter first. Before we quote the roof. Your 20-year window runs from the original year of interconnection, and we want to know how much of it is left before you spend money.
2. We locate the original approved plan set. The City requires it for the reinstall submittal. If you don't have it, we tell you that early, because tracking it down takes time and it's better to start on day one than on tear-off day.
3. We inventory the array before it comes off — module make, model, quantity, serials, inverter make and model, and the as-built string configuration — and we give you that inventory in writing.
4. We put the array back the way it came off. Same modules, same count, same inverter, same configuration, unless you have deliberately decided otherwise in a separate conversation with the threshold math on the table.
5. If a module is damaged, you hear about it before we order anything. Including what the replacement's nameplate rating is and what it does to your headroom.
6. If you do decide to change something, we tell you it's a change and we point you at SDG&E's modification application type rather than hoping it goes unnoticed. (See Form 142-02774.)
7. We hand you a closeout file with permits, inspection records, the before/after array inventory, and the roof warranty documentation, so that if anyone ever asks what happened to this system years from now, there's an answer in a folder.

If you're already mid-project

If a roofer has your panels on the ground right now, or you're holding a proposal that bundles "reroof + panel reset" with a line item you don't recognize, three things are worth doing today.

Get the proposal's equipment list and compare it to what's actually on your roof. Module count, module model, inverter model. If any of those three changed, that's a system modification, and you want to know about it before it's energized, not when a bill looks wrong.

Find your interconnection paperwork. Your permission-to-operate letter has your original nameplate capacity on it. That number is the baseline the 10%-or-1-kW test is measured against — SDG&E's tariff says capacity "as established when the Generating Facility was originally interconnected."

And if something has already changed, call SDG&E rather than guessing. They administer the tariff. We don't, and neither does the company that did the work.

Send us your plan set and we'll read it before you sign anything. No charge and no obligation — if the answer is "this is fine, your roofer is doing it right," we'll tell you that and you'll never hear from us again.

One honest note on adding capacity

People sometimes decide a reroof is the natural moment to grow the array. Sometimes it is. But be aware that the economics of adding residential solar capacity changed at the end of 2025: the federal residential energy efficient property credit under §25D terminated for expenditures made after December 31, 2025, and the IRS treats an expenditure as made when the installation is completed. A 2025 deposit did not preserve it. (Source: IRS, Residential Clean Energy Credit. Last verified August 21, 2026 — confirm current IRS guidance before relying on this.) Any proposal that still prices an addition around a residential federal credit is priced on something that no longer exists.

Commercial systems sit under a different section of the code with different timing. If this is a commercial building, that's a separate conversation — see our commercial solar page.

Frequently asked questions

Does replacing my roof by itself change my net metering tariff? The test written into SDG&E's tariff is about whether the generating facility's capacity increased, not about the roof underneath it. A reroof with a true like-for-like panel reinstall doesn't increase nameplate capacity. That said, eligibility is determined by SDG&E under CPUC rules, not by your contractor — so we describe the test rather than promise the outcome. (SDG&E Schedule NEM-ST, verified August 21, 2026.)

How much can I add before I have a problem? The greater of 1 kW or 10% of your system's original nameplate capacity. For most residential arrays under 10 kW, that means 1 kW. SDG&E states that exceeding it makes the customer responsible for non-bypassable charges on 100% of the net kWh delivered. (SDG&E Net Energy Metering, verified August 21, 2026.)

When does my 20 years actually run out? Twenty years from the original year of interconnection — not from installation, not from purchase. Your permission-to-operate documentation has the date. (CPUC, verified August 21, 2026.)

My inverter is old. Should I replace it during the reroof? Maybe — but understand it's a modification to an interconnected facility, and SDG&E has a specific application type for exactly that. (Form 142-02774.) The question to answer first is whether the inverter is genuinely near end of life or just old, because "it's already down" isn't a technical reason. If it doesn't need replacing yet, don't replace it yet.

What if a panel breaks during removal? It's a real possibility on any detach-and-reset, especially with older framed modules and brittle backsheets. What matters is that you find out immediately, that the replacement's nameplate rating is disclosed to you, and that you know what it does to your 1 kW of headroom before anything is ordered.

Do I need a permit just to take the panels off and put them back? The City of San Diego's bulletin addresses PV removed for renewal of the roof covering directly: the original approved record plan set must accompany the submitted PV plans, a pre-removal inspection may be required, the reinstallation permit does not allow alteration of the original equipment or system, and the PV work must be done by a contractor holding a C-10 or C-46 license. (Information Bulletin 301, rev. May 2026, verified August 21, 2026.) Requirements outside city limits are set by that jurisdiction.

Can my solar company do the roof, or my roofer do the panels? Not interchangeably. The City requires a C-10 or C-46 holder for the PV reinstall. Roofing is a separate classification. A contractor licensed only for solar under C-46 is barred by CSLB from performing other building trades except as required to install a thermal or photovoltaic solar energy system — meaning a solar-only license cannot legally re-roof your house. (CSLB C-46 classification, verified August 21, 2026.)

Who actually decides whether I keep my tariff? SDG&E, applying rules set by the California Public Utilities Commission. Not us. If a contractor tells you your grandfathering is guaranteed, ask them to put the guarantee in the contract with a dollar figure attached, and watch what happens.

Should I just wait and reroof later to be safe? Waiting doesn't protect your tariff — the tariff isn't at risk from the roof. What waiting does is let water get past a roof that's already at end of life, with an array bolted through it, which turns a reroof into a reroof plus decking plus interior repair. If the roof is done, the roof is done. See do I need a new roof before solar.