ADU builders
ADU sewer lateral: share the line or run a new one?
By the HyreADU research desk. Last checked .
The short answer
The sewer lateral is the pipe from your house to the public sewer. An ADU usually ties into the existing lateral if it has capacity and slope, which saves a new connection.
If the line is old, cracked or too small, or the ADU sits downhill of it, a new lateral or a pump may be needed. A camera inspection tells you which.
Start with a camera inspection
A plumber runs a camera down the existing lateral. It shows cracks, roots, sags and the pipe size. It also shows the depth, which decides whether the ADU’s drains can flow by gravity. Do this before drawings are final.
What the law says about connections
In California an ADU is not a new residential use for sewer connection fees or capacity charges, unless built with a new house (Gov. Code § 66311.5(b)).
For by-right ADUs, the agency cannot require a new separate connection to the utility (Gov. Code § 66323). Your sewer district may still have its own requirements for a damaged line.
Septic lots
On a septic system the question is tank and field capacity, not a lateral. County environmental health usually decides. See ADUs on septic systems.
What to do next: read the questions to ask an ADU builder, check what decides ADU cost, then tell us about your project. Matching is not live yet, so we reply with information, not a quote.
Get ADU optionsQuestions
Who repairs the sewer lateral?
In most cities the owner is responsible for the lateral up to the main. Check your city.
What if the ADU is lower than the street sewer?
A sewage ejector pump may be needed. Your plumber and city decide.
Does the city require lateral replacement?
Some cities have point-of-sale or remodel rules. Ask your public works department.
Is lateral work in the builder’s bid?
Often not. Ask for it as a priced line.
Sources
- Gov. Code § 66311.5 (ADU fees and utility connections). Checked September 5, 2026.
- Gov. Code § 66323 (by-right ADUs, utility connections). Checked September 5, 2026.
HyreADU is a publisher. It does not design, permit or build ADUs, has no partner builders, and gives no legal, tax or engineering advice. Rules vary by state and city; California rules are labeled as such.