Pre-Approved ADU Plumbing Plans in California: What AB 1332 Actually Speeds Up
For the big bills · $59California Homeowner Plumbing Pack33 chapters, read online: sewer line kit · slab leak and insurance claim kit with 3 letters · month-by-month maintenance calendar · Price Book (17 jobs, 145 cities) · Water Heater Kit. What's insideOne payment of $59 · instant access, receipt by email · for California homeowners
Get the pack · $59
If you've started researching an accessory dwelling unit in California in the last year, you may have run into a term that didn't exist a few years ago: a "pre-approved plan." It sounds like a shortcut, and for the structure itself, it largely is — a design that's already been checked against the plumbing, mechanical, electrical and energy code, sitting on your city's website, ready to build. What it is not is a shortcut around the part of an ADU that actually drives most of the cost and delay: the sewer, water and gas connections that run from the street or the main house to wherever the unit ends up. Here's what the law actually requires, what a pre-approved plumbing plan covers, and what still needs a plumber to look at your specific lot.
What AB 1332 actually requires
Assembly Bill 1332, codified as Government Code §65852.27, took effect statewide on January 1, 2025. It requires every California city and county to establish a program that reviews and pre-approves ADU plan sets — submitted by architects, designers, builders or nonprofits — and posts the approved sets publicly for any homeowner to use. A jurisdiction cannot restrict who is allowed to submit a plan for pre-approval, and once a plan is on the list, any property owner can pull it and apply. Then comes the part with real teeth: for a detached ADU built from a pre-approved plan, once you submit a complete application, the local agency must ministerially approve or deny it within 30 days. That's a statutory deadline, not a target — a meaningful change from the often open-ended, multi-round discretionary review that a fully custom ADU design can go through.
What's already checked off — and what still gets a site visit
A pre-approved set has already been plan-checked for plumbing, mechanical and electrical code compliance and for Title 24 energy calculations, for the structure as designed. What it hasn't checked is your actual lot. Utility connections — tying into the sewer lateral, upsizing or adding a water meter, running or extending a gas line — along with the site plan, grading, drainage and foundation design, are still reviewed individually at permit submittal, because those depend entirely on where your ADU sits relative to the existing house, the street, and what's already buried in your yard. Those are exactly the line items our ADU plumbing cost guide breaks down — a short tie-in to an existing lateral can run a few thousand dollars, while a new lateral run to the street on a deep lot climbs into five figures — and they're the reason two homeowners building the identical pre-approved floor plan on different lots can still end up with very different total costs and timelines. For the state-law backdrop on utility connection fees and when a separate meter can and can't be required, see our ADU plumbing requirements guide.
Where to actually find your city's plans
Coverage and depth vary a lot by jurisdiction. The Los Angeles Department of Building and Safety maintains one of the more developed catalogs, with more than 20 pre-approved standard ADU designs available on its site. San Jose runs its program through a list of pre-approved vendors rather than a raw plan library — you contract with one of them and they carry a design already through the city's process. Smaller cities are required to have a program too, but some are further along than others; a few post a genuine catalog of ready-to-pull plans, while others post a checklist for submitting your own plan for pre-approval rather than a library of finished ones. Check your own building department's ADU page before assuming a catalog exists or is current — and if you're comparing plumbers for the utility-connection side of the job in a city with an active program, our Los Angeles sewer line page and San Jose gas line page cover typical costs for that piece specifically.
The code-cycle wrinkle worth asking about
California updates its building standards code on a regular three-year cycle, and the 2025 California Building Standards Code — including its plumbing, mechanical and energy provisions — took effect January 1, 2026. A plan that was pre-approved under the prior code cycle isn't automatically invalid, but it's worth asking your building department whether the catalog you're looking at has been reconciled against the current cycle, particularly if the design has been sitting on the city's site for a while. This is a small thing to check before you commit months of planning to a specific floor plan.
Why this kind of streamlining tends to actually work
AB 1332 is too recent to have its own completions data yet, but California has run something like this experiment before. When the state loosened ADU permitting rules starting in 2017, researchers at UC Berkeley's Terner Center for Housing Innovation tracked what happened next: statewide ADU permits nearly tripled and completions more than tripled between 2018 and 2019 alone, once procedural friction came down (Chapple, Garcia, Valchuis & Tucker, Reaching California's ADU Potential: Progress to Date and the Need for ADU Finance, Terner Center, 2020). That's the pattern pre-approved plans are betting on again: the design itself was rarely the real obstacle to building an ADU — the uncertainty and time cost of getting through review was. Removing that for the structure doesn't remove it for the ground underneath it, which is exactly why the utility and site-specific side of the job is still worth budgeting and scoping carefully, pre-approved plan or not.
The practical takeaway
If you're set on a pre-approved design, the smartest early move isn't picking the floor plan first — it's getting a plumber to walk your actual lot before you fall in love with a specific layout. A quick look at where your sewer cleanout sits, how far the water meter is from the proposed unit, and whether the existing gas line has capacity to spare will tell you more about your real cost and timeline than the plan catalog will. Request a free quote and a local licensed plumber can scope the sewer, water and gas connection for your specific ADU site before you finalize which pre-approved plan to build.
Need a plumber you can trust?
Tell us about the job — a licensed California plumber gets back to you with a real quote.
Get free quotes