ADU type
Detached ADU
A detached ADU is a standalone second unit on the same lot as the primary home — its own foundation, walls, and roof. It earns the highest rents and the highest resale lift of any ADU type, and it's the only type that lets you fully control the floor plan instead of inheriting a garage envelope.
What it is
- Standalone structure with its own foundation, framing, and utilities — physically disconnected from the main house.
- Allowed up to 1,200 sqft statewide under California ADU law (SB 9 / AB 68), regardless of local zoning.
- Can be one or two stories where setbacks allow (16-ft maximum height for ministerial approval in most jurisdictions).
- Requires its own electrical service, water lateral, and sewer connection — or a sub-panel and shared laterals if utilities allow.
- Counts as a separate unit for refinancing, insurance, and (in most jurisdictions) for rental income on a loan application.
Los Angeles · 2026
$330K – $520K all-in
$425 – $620/sqft
Westside, hillside, and Coastal Commission areas trend toward the top of the band.
Bay Area · 2026
$420K – $700K all-in
$550 – $850/sqft
SF and Peninsula consistently top the band; Tri-Valley and East Bay flats sit mid-band.
When it fits
- Lot has 800+ sqft of usable rear or side yard after setbacks.
- You want maximum rental income — detached units typically rent 15–25% above garage conversions at the same size.
- You plan to sell within 5 years and want measurable resale lift.
- The existing house has structural or HVAC issues that would compound an attached build.
When it doesn't
- Lot coverage is already near the maximum (common in Westside LA and SF).
- Soil conditions require deep piles (steep Bay Area hillsides, expansive LA clay) — foundation cost can eat the budget.
- You're chasing the fastest possible move-in date — a garage conversion is 2–3 months quicker.
Permit pathway
Los Angeles
Ministerial review under state ADU law — LADBS typically issues in 60 days on a clean submittal. Hillside Ordinance and Coastal Commission overlay can add 30–60 days. Most LA cities follow the same clock.
Bay Area
Ministerial review applies statewide, but Bay Area utility coordination (PG&E service upgrade, SFPUC sewer lateral compliance) adds 60–120 days outside the permit clock. Plan early.
Realistic timeline
Design + engineering: 8–12 weeks. Permit: 8–16 weeks (longer with utility upgrade). Construction: 5–7 months from groundbreaking. Plan on 12–18 months door-to-door.
FAQ
- Can I build a detached ADU on any lot in California?
- If the lot has a single-family or multi-family home and meets the 4-ft side/rear setbacks, yes — state law (Gov. Code §65852.2) requires every California city to allow one detached ADU. Local height, FAR, and design rules apply, but a city cannot deny outright.
- Do I need a parking space for a detached ADU?
- Not if the property is within ½ mile of public transit (most LA and Bay Area lots qualify). Parking replacement is also waived when converting existing garage space.
- How much does the detached ADU foundation alone cost?
- $28K–$55K for a slab on grade in LA; $40K–$95K in the Bay Area where pier-and-grade-beam or drilled piers are common on sloped or expansive soil. We always pull a soils report before pricing.
- Will building a detached ADU raise my property taxes?
- Yes, but only on the new value added — Prop 13 protects the base assessment on your primary home. Expect a roughly 1.1% annual tax on the assessed cost of the ADU.