ADU utilities: meters, sewer, panels and what they cost

What state law says about ADU utilities

California splits ADUs into two groups for utility purposes. The rules sit in Government Code § 66311.5, which SB 543 renumbered from § 66324 on January 1, 2026. Older city documents and articles may still cite the old number.

For the second group, a city, special district or water company may require a direct connection between the ADU and the utility. Any connection fee or capacity charge must be proportionate to the burden of the ADU, measured by its square footage or its plumbing drainage fixture units, and can't exceed the reasonable cost of the service. The same section also keeps connection fees and capacity charges out of its definition of “impact fee,” so the state's ban on impact fees for ADUs of 750 square feet or less doesn't cover them.

San Diego's rule follows from that. The city's municipal code says an ADU must have a separate water, sewer or electrical connection if the utility serving the house asks for one. For the full set of size, setback and fee rules, see our guide to California ADU laws.

Does an ADU need a separate meter?

For electricity in San Diego, usually yes. Snap ADU, a San Diego builder, reports that SDG&E now requires a separate electric meter for new-construction ADUs. Its figures:

• Cost. Snap ADU's sitework guide puts a separate SDG&E meter at $10,500 to $15,000, and lists it as an extra outside its base ADU price.
• What's not in that number. Upgrading the weatherhead, underground conduit, relocating the main panel and work in the public right of way are extra.
• Time. The on-site work usually takes about two days, but the process from application to re-energizing can run six months or more. SDG&E's site evaluation alone can take two to four months and may add requirements.

That lead time is why your builder should apply to SDG&E early, long before framing. A separate meter also lets you bill a tenant directly, which matters if you plan to rent; see ADU rental income in San Diego.

For water and gas, a separate meter is a choice more often than a rule. Both are covered below.

ADU electrical panel and service upgrades

Your house gets power through a service drop from SDG&E to a main service panel. Snap ADU notes that panels come in sizes from 100 to 400 amps and that the service drop is typically 100, 200 or 400 amps. An ADU adds a kitchen, a water heater, heating and cooling, and often an EV charger, so an older 100-amp house service may not have room for it.

There are three common setups:

Snap ADU says the cost of a service upgrade varies widely depending on the reason for the upgrade and how close the site is to high-power lines. We didn't find a reliable published price for a San Diego panel upgrade, so get it quoted as its own line item.

The energy code also affects the panel. Under the 2025 code, a gas water heater or furnace needs a dedicated circuit and a reserved breaker space for a future heat pump. And the battery-ready rules don't apply to an ADU whose electric service is 125 amps or less. Solar rules for new detached units are in our ADU solar requirement guide.

ADU sewer connection cost

Most ADUs don't get their own connection to the city sewer main. The ADU's waste line runs to the house's existing sewer lateral, the pipe between the house and the main. In the City of San Diego, the property owner is responsible for the lateral all the way to the connection with the main, so its condition is your problem before and after the ADU goes in.

What drives the cost:

• Gravity. Sewage needs to flow downhill. If the ADU sits lower than the point where it ties in, Snap ADU puts a sewage pump at about $5,000.
• Distance. The same guide puts utility runs beyond its base sitework at up to $200 per linear foot.
• An undersized lateral. Snap ADU calls an upsized sewer lateral uncommon but possible, depending on the jurisdiction. A camera inspection of the line before design catches cracks, roots and sizing problems.
• Septic. Rural lots on septic face a much bigger bill. Snap ADU's sitework guide puts a septic system at about $30,000 to $40,000.
• City capacity charges. In the City of San Diego, water and sewer capacity fees are determined during plan review. A conversion can't be charged one under state law.

A flat lot with the house's sewer line running downhill toward the street is the cheapest case. A backyard that slopes away from the street is the most expensive. Our backyard ADU guide covers siting.

ADU water meter

Most San Diego ADUs share the house's water service. The city's ADU bulletin lists a Water Meter Data Card (form DS-16) with the permit application, and that card is used to determine the meter size the project needs. Adding a kitchen and bathroom raises the fixture count, which can push you to a larger meter.

A private submeter on the ADU lets you split the water bill with a tenant without opening a second utility account. Fire sprinklers, where required, can also trigger a bigger meter or lateral. Each city and water district sets its own meter rules, so ask yours before the plans are final.

Gas or all-electric

California's 2025 energy code, which applies to permit applications filed from January 1, 2026, makes heat pumps the prescriptive baseline for space and water heating in single-family homes, and the Energy Commission treats a new detached ADU as a newly constructed building under those rules. Gas is still possible, but each gas appliance brings electric-ready wiring and panel space for a future heat pump.

Going all-electric skips a gas line trench. If you do run gas, Snap ADU says the ADU's line typically branches off the house's private gas line after the meter, so that line must be sized for both homes. A separate gas meter isn't required when the ADU has no vented gas appliances, and if you want one anyway, Snap ADU puts it at about $5,000 to $10,000.

The trade-off: all-electric puts more load on the electrical service, which can push you toward a panel upgrade or a separate electric meter.

Planning ADU utilities before design

Utility surprises usually come from things nobody looked at before the plans were drawn. A few checks at the feasibility stage cost little and can move the ADU to a cheaper spot on the lot.

Before you pick a location

• Read your panel label. The main breaker shows your service size in amps. A small service is the first sign you may need an upgrade or a separate meter.
• Find the sewer cleanout and its depth. Your designer needs to know whether the ADU floor sits high enough for gravity flow. If it doesn't, budget for a pump or move the unit.
• Scope the lines. Snap ADU's feasibility process uses camera inspections of the sewer and water lines and ground-penetrating radar to map existing utilities before design. Even a basic plumber's camera run on the sewer lateral tells you whether it's cracked or full of roots.
• Trace the trench route. Every foot between the house's connections and the ADU is trench, and paths, patios and trees in the way add cost.

During design and permitting

• Choose gas or all-electric early. The decision sets the panel size and whether you need a gas trench at all.
• Settle the meter plan. Decide whether the ADU gets its own electric meter and a water submeter, and get the SDG&E application started as soon as the electrical design is ready.
• Fill out the Water Meter Data Card accurately. The fixture count on it drives the meter size and any capacity fee.
• Get utility items priced separately. A bid that rolls utilities into “sitework” makes it hard to see what's missing. Ask for the meter, panel, sewer, water and gas work on their own lines, with allowances spelled out.

Utility work happens early in the build, right after site prep and before or alongside the foundation, so delays here hold up everything after. Our ADU construction process guide shows where it fits.

ADU utilities budget

Put these numbers next to what an ADU costs in San Diego. Snap ADU's base price includes about $35,000 of level-lot sitework, including basic trenching and hookups; the items below are extras that show up on harder sites.

The Contractors State License Board warns that trenching for water, sewer and power is easy to leave out of a bid. When you compare bids, ask each builder to list utility work line by line, and say who handles the SDG&E application. Our guide on how to hire an ADU contractor has the rest of the checklist, and you can check a contractor's license or compare verified ADU builders in San Diego.

Common questions