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The short answer
In Los Angeles in 2026, plan on roughly one year from first call to move-in for a detached ADU. That breaks into about 3-6 months for design and permits and 6-9 months of construction. Garage conversions are faster — 3-5 months of build time — and a junior ADU (JADU) inside your existing home can be done in 2-4 months. The build itself is rarely the bottleneck; permit timing and site access are what stretch the calendar.
| ADU type | Permit phase | Build phase | Realistic total |
|---|---|---|---|
| Detached new build | 3-6 months | 6-9 months | ~10-15 months |
| Garage conversion | 3-6 months | 3-5 months | ~7-11 months |
| Attached addition | 3-6 months | 5-7 months | ~9-13 months |
| Junior ADU (JADU) | 2-4 months | 2-4 months | ~5-8 months |
The rest of this guide walks through each phase so you know what’s happening — and where the delays usually hide.
Phase 1 — Design and planning (3-6 weeks)
Before anything gets submitted to the city, you need a design and a set of plans. For a standard ADU this means a site plan, floor plans, elevations, and the structural and MEP (mechanical, electrical, plumbing) details the city needs to review.
If you use a pre-approved or “spec” plan, this phase is short. LA City maintains a streamlined program with 60-day approval for spec plans, which can compress the front end significantly. If you want a fully custom design, expect this phase to run longer because every revision adds a round of drawing.
Phase 2 — Permitting (3-6 months)
This is the phase homeowners underestimate most. Submitting plans to LA City (or the relevant county/city jurisdiction) kicks off plan check, where reviewers flag corrections. You revise, resubmit, and wait for the next review. Two or three correction cycles is normal.
A few things speed this up in LA:
- Streamlined 60-day approval is available for spec plans in LA City.
- State law overrides HOA and CC&R restrictions on ADUs (since 2020), so you don’t lose months fighting an HOA.
- Impact fees are waived for ADUs under 750 sq ft in LA City, which removes one paperwork and payment step.
What slows it down: custom plans with multiple correction cycles, hillside or small-lot complications, and utility coordination (a new sewer connection or panel upgrade can add review time).
Phase 3 — Construction (varies by type)
Once you have permits in hand, the build clock starts. Construction time tracks closely with how much you’re building from scratch:
- Detached new build (600-1,200 sq ft): 6-9 months. You’re pouring a foundation and building a shell, roof, and full interior.
- Garage conversion (400-600 sq ft): 3-5 months. The foundation, walls, and roof already exist, so you’re mostly doing interior framing, insulation, MEP, and finishes.
- Attached addition (400-800 sq ft): 5-7 months. Tying into the existing house adds coordination but you share a wall and some systems.
- JADU (up to 500 sq ft, inside the home): 2-4 months. It’s an interior conversion, often of a bedroom or attached space.
Within construction, the cost-and-time driver order is foundation and site work first, then permits, then finish level, then MEP rough-in, then kitchen and bath, then exterior. Site access matters more than people expect — a tight lot where materials have to be carried by hand moves slower than one a truck can pull up to.
Phase 4 — Inspections and final sign-off (within the build)
Inspections happen throughout construction, not just at the end — foundation, framing, rough MEP, insulation, and final. Each one has to pass before the next phase of work can be covered up. A failed inspection means a correction and a re-inspection, which can add days. A good contractor schedules these tightly so the crew isn’t sitting idle waiting on the inspector.
The final inspection and certificate of occupancy is what legally clears you to move in or rent the unit.
Where the delays actually come from
Across LA ADU projects, the most common timeline-killers are:
- Permit correction cycles — the single biggest variable. Clean, code-correct plans submitted the first time save months.
- Utility upgrades — a new sewer lateral, water meter, or electrical panel upgrade adds review and scheduling time.
- Site access — hillside lots, narrow side yards, and no truck access slow every delivery.
- Change orders mid-build — deciding to move a wall or upgrade finishes after framing restarts parts of the schedule.
- Contractor backlog — a good crew may not be able to start the day you get your permit.
How to keep your ADU on schedule
The fastest LA ADU projects share a few things. They use streamlined or spec plans where possible to shorten permitting. They lock the design before submitting so there are no mid-build change orders. They handle utility questions early instead of discovering them at plan check. And they hire one team that both quotes and builds the project, so nothing falls through the gap between designer and contractor.
Building Greatness Inc is a licensed LA contractor (CSLB Lic. #1089704) that handles ADU projects end to end across Los Angeles County — design, permitting, and construction under one roof — so the handoffs that usually add weeks don’t happen.
FAQ
How long does it take to build an ADU in LA?
Plan on about a year start to finish for a detached ADU in LA — roughly 3-6 months for design and permits and 6-9 months of construction. Garage conversions are faster at 3-5 months of build time, and a JADU inside your home can be done in 2-4 months.
What takes the longest when building an ADU?
Permitting is usually the longest and least predictable phase, running 3-6 months because of plan-check correction cycles. The construction itself is more predictable once permits are issued.
Can you build an ADU faster with pre-approved plans?
Yes. LA City offers streamlined 60-day approval for spec (pre-approved) plans, which can significantly shorten the permitting phase compared to a fully custom design that needs multiple review rounds.
How long does a garage conversion ADU take in LA?
A garage conversion typically takes 3-5 months to build once permitted, because the foundation, walls, and roof already exist. Including design and permits, expect roughly 7-11 months total.
Do permits really take 3 to 6 months in Los Angeles?
For a custom ADU, yes — plan check usually involves two or three correction cycles. Using LA City’s streamlined spec-plan program with 60-day approval can shorten this considerably.
How long does it take to build a JADU in LA?
A junior ADU (up to 500 sq ft, converted from existing space inside your home) is the fastest option — about 2-4 months to build and roughly 5-8 months total including permits.