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Vol. I ·California ADU Desk ·Licensed · Bonded · Insured ·CSLB #1098432 ·BBB A+ Accredited ·120+ ADUs Delivered ·Starting $250K ·10–16% ROI ·Los Angeles ·Bay Area ·Vol. I ·California ADU Desk ·Licensed · Bonded · Insured ·CSLB #1098432 ·BBB A+ Accredited ·120+ ADUs Delivered ·Starting $250K ·10–16% ROI ·Los Angeles ·Bay Area ·
GoldenStateADU

Design · 6 min read · February 15, 2025 · 295 words

Detached, attached, or conversion: choosing the right ADU type

A decision framework for picking the configuration that fits your lot, budget, and rental strategy — with the trade-offs builders rarely volunteer.

Key takeaways

  • Best for: lots with usable rear yard space, ROI-focused owners.
  • Typical cost: $300–$425 per sq ft.
  • Permit + build timeline: 9–13 months.

There are three primary ADU configurations in Los Angeles: detached new construction, attached new construction, and garage or accessory structure conversion. Each has a clean profile of cost, timeline, ROI, and constraint — and the right answer is almost always determined by your lot before it is determined by your taste.

Detached ADU

A standalone structure separated from the main home. Most flexibility on layout, the highest market rent per square foot, and the cleanest separation for short- or long-term rental. Also the most expensive — full new construction with its own foundation, exterior envelope, and utility runs.

  • Best for: lots with usable rear yard space, ROI-focused owners.
  • Typical cost: $300–$425 per sq ft.
  • Permit + build timeline: 9–13 months.

Attached ADU

Shares one or more walls with the primary home. Cheaper per square foot than detached because envelope and utilities are partially shared, but design is constrained by the existing home's footprint, roof line, and structure.

  • Best for: lots with limited rear yard, owners adding a second story or wing.
  • Typical cost: $250–$360 per sq ft.
  • Permit + build timeline: 8–12 months.

Garage / accessory conversion

Converting an existing garage, workshop, or accessory structure. Setback and parking requirements are typically waived, foundation work is minimal, and the envelope already exists. Most affordable path — but constrained to the existing footprint.

  • Best for: tight budgets, fast timelines, lots with a serviceable existing structure.
  • Typical cost: $180–$275 per sq ft.
  • Permit + build timeline: 6–10 months.

How to choose

  1. If your primary motive is the highest possible ROI and your lot supports it — detached.
  2. If you have an existing garage and want to enter the market quickly — conversion.
  3. If your lot is shallow but deep, or you're already planning a second-story addition — attached.

FAQ · Design

Common questions on design

The questions readers send us most after this guide.

  1. I'm in an HPOZ — can I still build?
    Yes, but with design review. Historic Preservation Overlay Zones require Certificate of Appropriateness from the cultural heritage commission before permits issue. We've shepherded projects through Miracle Mile, West Adams, Whitley Heights, and Spaulding Square HPOZs. Add 8–12 weeks for the COA process.
  2. What setbacks and height limits apply?
    Statewide ADU law (AB 68/881) overrides most local restrictions: 4-foot side and rear setbacks, 16-foot height for detached one-story, 18-foot for two-story within ½ mile of transit. Front setbacks follow the underlying zone. We model your envelope at the schematic stage.
  3. Do you handle the permitting?
    Yes. We file with LADBS or your local building department, manage plan check, coordinate utility upgrades, schedule inspections, and deliver final sign-off. You don't visit the counter, we do.
  4. What is SB-9 and does it apply to me?
    SB-9 (the California HOME Act) lets eligible single-family lots split into two parcels and/or add a duplex. We assess eligibility during the feasibility call — roughly 60% of LA single-family lots qualify on paper, fewer in practice once HPOZ, hillside, and coastal overlays are applied. SB-9 projects can stack with an ADU for up to four units on what was a single-family lot.
  5. What about hillside or coastal lots?
    Hillside requires a Methane District review (where applicable) plus a haul route plan if grading exceeds 1,000 cubic yards. Coastal Zone projects (anything west of Lincoln Blvd in Venice, for example) need a Coastal Development Permit on top of standard LADBS approval. Both are workable; both add 60–90 days.

Sources & further reading

  • California Government Code §65852.2 — statewide ADU framework (ministerial review, 60-day clock).
  • LADBS — Accessory Dwelling Unit information bulletins and current permit fee schedule.
  • HCD — California Department of Housing & Community Development, ADU handbook (2024 update).
  • Internal data: 120++ ADU projects delivered across Los Angeles County, 2018–2025.

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