Design · 6 min read · February 15, 2025 · 347 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–$400 per sq ft.
- Permit + build timeline: 9–13 months.
Answered in this guide
Jump straight to the question you came in with — every answer is on this page, with links onward to the deeper guide.
- I'm in an HPOZ — can I still build?
- What setbacks and height limits apply?
- Do you handle the permitting?
- What is SB-9 and does it apply to me?
- What about hillside or coastal lots?
- Are you licensed and insured?
More across the studio · the full FAQ map · the reference desk
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. Pair this with the cost anatomy for the dollar numbers under each route.
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–$400 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
- If your primary motive is the highest possible ROI and your lot supports it — detached. Validate against the rental yield guide.
- If you have an existing garage and want to enter the market quickly — conversion.
- If your lot is shallow but deep, or you're already planning a second-story addition — attached.
Sources
- Statewide ADU Standards — Gov. Code §65852.2 · California Legislature
- JADU Standards — Gov. Code §65852.22 · California Legislature
- California ADU Handbook (2024) · California HCD
- LADBS ADU Information Bulletin · LA Department of Building and Safety
Next chapter · 01 of 03
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Designing an ADU you actually want to live in
Form picked. Now design the rooms people actually want to live in — twelve moves, most of them free.
Twelve design moves that separate a great 700 sq ft ADU from a generic one — most cost nothing extra, all of them protect your re-sale and rental value.
FAQ · Design
Common questions on design
The questions readers send us most after this guide.
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.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.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.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.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.Are you licensed and insured?
Yes — CSLB #1156772. License, bond, general liability and workers' comp certificates are shared during your consultation; full coverage details are confirmed in writing before signing.
Reference desk · Design
More answers from the California reference desk
City-specific questions pulled from our 5,000-answer FAQ corpus — every link opens a deeper desk page.
What size ADU makes sense in Beverly Hills?
In Beverly Hills, the sweet spot for ROI is 600–850 sq ft (one-bedroom) — large enough to rent at $3,400/mo, small enough that $/sqft stays controlled and the permit path stays state-law-protected. Footprint and roof shape matter more than total square footage for the final number.What Title 24 requirements apply to a ADU in Beverly Hills?
CA Title 24 Part 6 (2022) requires high-efficiency envelope, mechanical, and lighting on any conditioned addition or new structure. The 2023 update mandates heat pumps for space and water heating on most new residential scopes — gas is allowed only with specific exceptions. Compliance is documented through a Title 24 report bound into the permit submittal; expect $1,800–$3,400 in compliance fees plus the equipment cost premium of $4K–$9K versus a gas system.What finish level should I specify for a ADU in Beverly Hills?
Spec for the rent target, not for personal preference. A $3,200/mo rental wants Bosch 500, quartz, LVP, and clean tile — not Sub-Zero and marble. In Beverly Hills, the workhorse tier (LG STUDIO appliances, KraftMaid cabinets, quartz, porcelain tile) delivers 85% of the daily-use experience of luxury tier at 55–60% of the cost.What layout works best for a ADU in Beverly Hills?
For a Beverly Hills ADU, the most successful layouts share three traits: (1) entry separated from the primary home for tenant privacy, (2) kitchen + bath stacked on a shared wet wall to reduce plumbing cost, (3) one larger main living area instead of two cramped rooms. Skip the breakfast bar — eat-in counters underperform a small dining nook in tenant satisfaction surveys.What exterior materials hold up best in Beverly Hills?
Beverly Hills climate rewards a small, proven palette: stucco or fiber-cement siding (James Hardie HZ10), Class A roofing (asphalt 30-yr architectural or standing-seam metal), aluminum-clad wood or fiberglass windows (Marvin, Sierra Pacific), and a low-maintenance landscape that doesn't trap moisture at the foundation. Avoid untreated wood siding in WUI fire zones — Class A assemblies are required.What size garage conversion makes sense in Beverly Hills?
In Beverly Hills, the sweet spot for ROI is 600–850 sq ft (one-bedroom) — large enough to rent at $3,400/mo, small enough that $/sqft stays controlled and the permit path stays state-law-protected. Footprint and roof shape matter more than total square footage for the final number.What Title 24 requirements apply to a garage conversion in Beverly Hills?
CA Title 24 Part 6 (2022) requires high-efficiency envelope, mechanical, and lighting on any conditioned addition or new structure. The 2023 update mandates heat pumps for space and water heating on most new residential scopes — gas is allowed only with specific exceptions. Compliance is documented through a Title 24 report bound into the permit submittal; expect $1,800–$3,400 in compliance fees plus the equipment cost premium of $4K–$9K versus a gas system.What finish level should I specify for a garage conversion in Beverly Hills?
Spec for the rent target, not for personal preference. A $3,200/mo rental wants Bosch 500, quartz, LVP, and clean tile — not Sub-Zero and marble. In Beverly Hills, the workhorse tier (LG STUDIO appliances, KraftMaid cabinets, quartz, porcelain tile) delivers 85% of the daily-use experience of luxury tier at 55–60% of the cost.What layout works best for a garage conversion in Beverly Hills?
For a Beverly Hills garage conversion, the most successful layouts share three traits: (1) entry separated from the primary home for tenant privacy, (2) kitchen + bath stacked on a shared wet wall to reduce plumbing cost, (3) one larger main living area instead of two cramped rooms. Skip the breakfast bar — eat-in counters underperform a small dining nook in tenant satisfaction surveys.What exterior materials hold up best in Beverly Hills?
Beverly Hills climate rewards a small, proven palette: stucco or fiber-cement siding (James Hardie HZ10), Class A roofing (asphalt 30-yr architectural or standing-seam metal), aluminum-clad wood or fiberglass windows (Marvin, Sierra Pacific), and a low-maintenance landscape that doesn't trap moisture at the foundation. Avoid untreated wood siding in WUI fire zones — Class A assemblies are required.What size JADU makes sense in Beverly Hills?
In Beverly Hills, the sweet spot for ROI is 600–850 sq ft (one-bedroom) — large enough to rent at $3,400/mo, small enough that $/sqft stays controlled and the permit path stays state-law-protected. Footprint and roof shape matter more than total square footage for the final number.What Title 24 requirements apply to a JADU in Beverly Hills?
CA Title 24 Part 6 (2022) requires high-efficiency envelope, mechanical, and lighting on any conditioned addition or new structure. The 2023 update mandates heat pumps for space and water heating on most new residential scopes — gas is allowed only with specific exceptions. Compliance is documented through a Title 24 report bound into the permit submittal; expect $1,800–$3,400 in compliance fees plus the equipment cost premium of $4K–$9K versus a gas system.
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: aggregated from real California ADU and residential construction projects, 2018–2025.
Continue your read · the editorial path
We chained these chapters in the order LA homeowners actually need them. Each one picks up where the last one left a question open.
02 / 03
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Title 24 for ADUs: what actually triggers compliance
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