ADU Builder's Guide
California is in the middle of an ADU boom — SB 9 unlocked lot splits, AB 1033 unlocked condominium resale, and LA approved 7,200+ ADUs in 2024 alone. This guide is the 7-step homeowner checklist for building one honestly: which archetype fits your lot, what SB 9 and AB 1033 actually unlock, why utility hookups are the hidden $20K-45K line item, and how to hire a contractor who has built more than two ADUs.
The 7 steps to a finished ADU
- 1
Decide what kind of ADU you actually want — 4 archetypes
California allows four distinct ADU archetypes and the math for each is different. (1) Junior ADU (JADU, under 500 sqft, interior conversion, must share utilities with main house — $80K-150K in LA); (2) Attached ADU (500-1,200 sqft, shares one wall with the main house — $180K-340K); (3) Detached ADU (500-1,200 sqft standalone — $220K-420K); (4) Two-on-one (detached ADU + JADU on the same lot, total $300K-550K). AskBaily's /adu-construction-los-angeles pillar has the full matrix. Your lot zone (R1/R2/R3), setbacks, and existing footprint determine which archetype your parcel actually supports.
- 2
Understand SB 9 and whether it applies to you
California SB 9 (2022) lets single-family lot owners in R1 zones split the lot AND add a second unit on each resulting lot — up to 4 units on what was originally one parcel. The catch: SB 9 lot splits require a 10% frontage allowance, both resulting lots must be at least 1,200 sqft, and one of the resulting owners must live on-site for 3 years post-split. SB 9 unlocks substantial upside on large LA lots but adds 4-8 months of process and survey cost. See /ask/what-is-sb-9-in-california for the full eligibility matrix.
- 3
Confirm AB 1033 status — can you sell the ADU separately?
California AB 1033 (2024) lets cities opt into allowing ADU resale as a condominium — meaning the main house and the ADU can be sold to separate owners. Los Angeles opted in 2024 with the AB 1033 ordinance. If you plan to rent the ADU long-term, AB 1033 does not matter. If you plan to resell or exit the ADU separately from the main house, AB 1033 adds ~$8,000 in condo-conversion legal work but can lift the ADU's sale price by $200K-400K because it unlocks conventional mortgage financing for the ADU buyer. See /ask/what-is-ab-1033-adu-sale.
- 4
Price the utility hookups honestly — this is where budgets explode
Every ADU contractor quote hides the utility story. Three line items to verify: (1) LADWP / SCE electrical service — a new 100-amp panel and sub-service for a detached ADU costs $8K-22K and takes 6-12 weeks of LADWP queue; (2) water meter + sewer lateral — in LA a new sewer tie-in is $6K-18K depending on street cut depth; (3) gas service — if the ADU has a gas range or tankless water heater, SoCalGas wants a new meter for $4K-12K. A $280K detached ADU base can easily become $340K after honest utility costs. Demand itemized utility scope in every quote.
- 5
Navigate Title 24 for the ADU specifically
California Title 24 governs ADU energy efficiency the same way it governs main-house remodels — but with tighter constraints because ADUs are newer construction. Expect: R-22 wall insulation, R-38 ceiling insulation, dual-pane Low-E windows, heat pump HVAC (new-construction ADUs built post-2023 must use electric heat pumps, not gas furnaces), and rooftop PV solar (required on detached ADUs in LA starting 2023). Budget $8K-18K for Title 24 consultant fees, plan-check revisions, and energy-compliance upgrades. Skipping Title 24 planning before permit submission is the #1 cause of 3-month plan-check delays.
- 6
Verify the contractor has ADU-specific experience
ADU contractors split into two camps: those who treat ADU as a kitchen-sized remodel (wrong — ADU is a freestanding dwelling with its own envelope, HVAC, utilities, Title 24 path) and those who have built 10+ ADUs and know LADBS's ADU Express Plan-Check program. Ask any ADU contractor for: (1) Active CSLB Class B license; (2) at least 5 completed LA ADU projects in 2024-2026 (demand Certificate of Occupancy copies); (3) LADWP service-upgrade experience; (4) familiarity with your specific zoning. Verify at /tools/contractor-check. Our LA-partner Netanel Presman (CSLB 1105249) has completed 12+ LA ADU projects including SB 9 lot splits.
- 7
Model the ROI honestly — 2026 LA ADU numbers
A realistic detached ADU in LA in 2026: $320K total all-in cost (construction + utilities + design + permits + Title 24). Median rental income: $2,800-4,200/month for a 1-bedroom, $3,800-5,400 for a 2-bedroom. Simple cash-on-cash yield at 70% leverage: 7-11% depending on neighborhood. Appreciation adds another 4-6%. AB 1033 resale exit: a Palisades or Sherman Oaks detached ADU can resell for $550K-850K once the main-house + ADU condo conversion is filed. See /ask/how-much-does-an-adu-cost and /ask/do-adus-increase-property-value for the full financial model.
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Ready to scope your ADU?
Tell Baily your address and what you want to build. We check SB 9 + AB 1033 + Title 24 + utility-upgrade requirements, then match you with one ADU-specialist contractor — not broadcast to eight.