Quick answer
An ADU utility connection is the way an accessory dwelling unit gets water, sewer, electricity and, where used, gas: either as a branch off the main house's existing service, or as a new, separate connection running directly from the utility to the unit.
Which one you need, and what the water or sewer agency may charge, is one of the larger variable costs in an ADU budget. California law limits both for many ADU types.
Quick facts
- Two routes
- Branch off the house service, or a new separate connection to the utility
- California: is an ADU a "new residential use" for connection fees?
- No, unless built with a new single-family home 1
- California: separate connection for a 66323 ADU
- Cannot be required (exceptions: built with a new home, or separate conveyance) 1
- California: other ADUs
- Separate connection may be required; fee proportionate to square feet or drainage fixture units 1
- Impact fee exemption
- ADUs of 750 sq ft or less of interior livable space; does not cover connection fees 1
- Junior ADU
- Not a separate or new dwelling unit for water, sewer or power service 3
Key takeaways
- A utility connection is how an ADU gets water, sewer, power and, if used, gas.
- You can branch off the main house, or run a new, separate connection from the utility.
- In California a separate connection cannot be required for an ADU built inside a home or existing accessory structure, with two exceptions.
- For other ADUs, such as a new detached unit, an agency may require one, but the fee must be proportionate.
- The 750 sq ft impact fee exemption does not cover connection fees.
- Utility meter work follows the utility's own filed rules.
What it means, in plain English
Every home needs pipes and wires. A utility connection is the link between your ADU and those services. It can come through the main house, or straight from the street.
A few terms help. A capacity charge is a fee for your share of the water or sewer system. A sewer lateral is the private pipe from your lot to the public sewer. A drainage fixture unit (DFU) is a plumbing code unit that scores how much a sink, toilet or shower drains.
Why it matters to you
Utilities are one of the larger swing items in an ADU budget. The same unit can cost very different amounts to connect on two lots. Distance, slope and the agency's fees all play a part.
The route also shapes the design. A long trench to the street can cross a driveway or tree roots. A branch from the house can be shorter, but it must fit what the house service can carry.
Last, it shapes billing. A shared connection means one bill for both homes. A separate one means the ADU can have its own account.
What "connecting" an ADU means
A new unit needs the same services as any home. Water usually comes from a branch of the main house supply line, or a new meter at the street.
Sewer drains into the house's private lateral or, less often, a new lateral to the main.
Electricity runs either as a feeder from the main house panel to a subpanel in the ADU, or as a new service and meter from the utility.
Gas, where used, follows the same two patterns, and an all-electric unit skips it. The diagram shows each service and the choice it involves.
The physical work is the easy part to price. The variable part is what each agency charges and whether it insists on a separate service. That is where state law steps in, at least in California. The utility connection research lays out the rules and the open conflicts in full.
- WaterBranch off the house supply, or a new meter at the street
- SewerTie into the house’s private lateral, or a new lateral to the main
- ElectricityFeeder from the house panel to an ADU subpanel, or a new service and meter
- Gas (if used)Branch off the house line, or a new meter; an all-electric unit skips it
Which option a utility or agency may require is a separate question; in California see Gov. Code § 66311.5 below.
California's connection rules by ADU type
| ADU type | Separate connection required? | Connection fee or capacity charge |
|---|---|---|
| ADU or JADU created within an existing or proposed single-family home or accessory structure under 66323(a)(1) | Cannot be required, unless built with a new single-family home or separately conveyed | Cannot be imposed on the same terms |
| Any other ADU, such as a new detached unit | May be required by the local agency, special district or water corporation | Must be proportionate to the burden, based on square feet or drainage fixture units (DFU), and not exceed the reasonable cost of service |
| Any ADU or JADU | Not treated as a "new residential use" for calculating connection fees, unless built with a new single-family home | See row above |
Three charges people confuse
| Charge | What it pays for | California ADU rule |
|---|---|---|
| Impact fee | Public facilities a new home burdens, such as parks and roads | None on ADUs of 750 sq ft or less; above that, proportionate to the main home's square footage (66311.5(c)) |
| Connection fee or capacity charge | A share of the water or sewer system's capacity | Excluded from the impact-fee exemption; limited by 66311.5(b), (d), (e) |
| Meter or service installation | The physical meter, tap and service line | Set by the utility's filed tariff, not by 66311.5 |
Sources: [1]
Example: how a proportionate charge scales
A hypothetical sewer agency whose charge for a full single-family home is a stated $X, used only to show the arithmetic the statute allows. Drainage fixture unit values come from the plumbing code the agency uses.
| Input | Main home | Detached ADU |
|---|---|---|
| Drainage fixture units (hypothetical count) | 20 DFU | 10 DFU |
| Share of the burden | 100% | 50% |
| Proportionate charge | $X | 0.5 × $X, capped at the reasonable cost of service |
Agencies may use square feet instead of DFU. Real charges come from the agency's fee schedule; see the fees by city research and the fee estimator.
Where the connection shows up in the project
- Feasibility: confirm where the water, sewer and electric services enter the lot and their capacity.
- Design: the plans show the routing; the electrical design depends on a load calculation.
- Permit: the building department reviews the utility plan; water and sewer agencies may issue their own approvals.
- Fees: connection or capacity charges are assessed by the agency that provides the service.
- Construction: trenching and tie-ins, then the utility sets any new meter.
Shared and separate connections compared
| Branch off the house | Separate connection | |
|---|---|---|
| What it is | New lines tie into the house supply, drain or panel | New service runs from the utility straight to the ADU |
| Billing | One bill for both homes | The ADU can have its own account |
| Capacity | Limited by what the house service carries | Set by the utility's design for the new service |
| Site work | Often a shorter trench | Often a longer trench to the street |
| California rule | Allowed | Cannot be required for 66323(a)(1) units, with two exceptions |
Where you will see it
- The site plan. It shows where each line runs from the house or street to the ADU.
- A contractor bid. Trenching, piping and tie-ins appear as line items.
- A fee letter. The water or sewer agency lists its connection fee or capacity charge.
- A utility application. New electric service or a meter needs the utility's own request. In PG&E territory, service work follows its filed Electric Rule 16 4.
Separate connections: benefits and limits
Benefits
- The ADU can be billed on its own
- It can avoid loading the house service
- It suits a unit that may be sold apart later, where allowed
Limits
- More trenching and site work
- A connection fee may apply for a detached unit
- More agencies to deal with before you can move in
Common misreadings
What to ask the city, water agency and utility
- Will you require a separate connection for this ADU type? Which rule supports it?
- How is your connection fee worked out: square feet or drainage fixture units?
- Where can I see your current fee schedule?
- Can the existing sewer lateral take the ADU, or will it need an inspection?
- What does the electric utility need before it sets a new meter?
- How long does each agency take to approve and connect?
Checklist for your project
- Locate where water, sewer, power and gas enter the lot.
- Have a licensed professional check the house electrical capacity.
- Choose shared or separate routes for each service.
- Ask each agency for its fee in writing.
- Show every route on the site plan.
- Put connection fees in the budget apart from impact fees.
- Book utility work early, since it follows the utility's schedule.
Outside California
Connection rules and fees are set by each state's law and each utility. Many places treat an ADU as a new connection and charge a full fee; others discount it. California's limits do not travel.
Questions about adu utility connection
Does an ADU need separate utility connections in California?
Not for an ADU or JADU built within an existing or proposed single-family home or accessory structure under Section 66323(a)(1); Section 66311.5(d) bars that requirement. For other ADUs, such as new detached units, the agency may require one.
Do ADUs pay utility connection fees?
In California an ADU is not a "new residential use" for connection fees unless built with a new home. A detached ADU that must take a separate connection can be charged a fee proportionate to its square feet or drainage fixture units.
Does the 750-square-foot fee exemption cover connection fees?
No. Section 66311.5(c)(2) excludes connection fees and capacity charges from the impact-fee exemption.
Can an ADU share the main house's water and sewer?
Often, yes. Branching off the existing line is common, subject to the plumbing code, capacity and the water or sewer agency's rules.
Is a junior ADU a separate unit for utilities?
No. Section 66338 says a JADU is not a separate or new dwelling unit for water, sewer or power service, including connection fees.
What utilities does an ADU need?
Water, sewer and electricity, plus gas if the design uses it. An all-electric ADU skips gas. Each can branch off the main house or come through a new, separate connection.
How is an ADU sewer connection fee worked out in California?
Where a separate connection is allowed, the fee must be proportionate to the burden of the ADU. Section 66311.5 bases that on square feet or drainage fixture units, capped at the reasonable cost of service.
Can my ADU use the main house's electrical service?
Often, through a subpanel fed from the house panel. A load calculation by a licensed professional decides if the house service can carry both homes.
Who sets the fee for a new electric meter?
The electric utility, through its tariff on file with the state regulator. In PG&E territory, service extension work follows Electric Rule 16.
Where did California's ADU connection fee rule move?
It was Section 66324. SB 543 (Stats. 2025, ch. 520) renumbered it to Section 66311.5 from 1 January 2026. Before 2024 the rule sat in former Section 65852.2.
Does a garage conversion ADU need a new utility connection in California?
Usually not. A garage is an existing accessory structure, so a conversion under Section 66323(a)(1) cannot be made to take a new or separate connection, or pay a connection fee or capacity charge for one. The exceptions are a unit built with a new home or sold separately.
Sources
- California Legislative Information, Gov. Code § 66311.5, retrieved .
- California Legislative Information, Gov. Code § 66323, retrieved .
- California Legislative Information, Gov. Code § 66338, retrieved .
- PG&E, Electric Rule No. 16, Service Extensions, retrieved .
- PG&E, Electric Rule No. 18, Supply to Separate Premises and Submetering of Electric Energy, retrieved .
Expert review
Written by the HyreADU Research team. Not yet reviewed by an outside expert. We say so rather than imply a review that has not happened; see our editorial policy.
How the numbers were checked: Connection and fee rules were read in Gov. Code §§ 66311.5, 66323 and 66338 on leginfo on 7 October 2026, with their enactment lines. The fee example uses hypothetical inputs for arithmetic only.
Suggest a correction. We fix errors and say what changed.