How Long Does an ADU Take From First Call to Sign-Off?
Plan on 12-20 months end to end for a Los Angeles ADU: roughly 2-4 months of design and engineering, 3-6 months through permitting, and 6-10 months of construction and inspections. The permit window is the part people quote and the part that varies least; design decisions before it and inspections after it are where most of the real time goes. We have not completed an ADU or a garage conversion with a published final cost, so everything on this page is process and Los Angeles market knowledge rather than a summary of our own finished work.
Stage one: design and engineering, 2-4 months
This is the stage owners consistently underestimate. It covers surveying what is actually on the lot, testing whether the unit fits within setbacks and coverage, resolving where power, water and drainage will come from, and producing a drawing set complete enough to submit.
The single biggest cause of delay here is not the drawing - it is decisions. A layout revisited in month three restarts work that had already been engineered.
Stage two: permitting, 3-6 months
California state law sets a 60-day statutory window for a city to approve or deny a complete ADU application. In practice the total is longer, because the clock applies to a complete submittal and the first submittal frequently is not one - corrections come back, get addressed, and go in again.
We set the permit stage out in more detail for one area in the Brentwood ADU permit timeline. The pattern is broadly the same across the city; what changes is which department is reviewing it.
Stage three: construction, 6-10 months
For a detached new-build this is foundations, framing, services, envelope, then interior finishing, with inspections at each stage. A garage conversion is generally shorter because the structure already exists - though it introduces its own question, which is whether what is already there can carry the new use.
Utility connections are the item most likely to sit outside your builder control. Where a new service or an upgraded panel is involved, that is a third-party schedule.
Stage four: inspections and final sign-off
Final sign-off is not a formality at the end of construction - it is a sequence of inspections through it, each of which has to pass before the next stage can be closed up. A failed inspection is rarely dramatic but it does mean re-scheduling, and re-scheduling is measured in days rather than hours.
The practical advice is unglamorous: do not book movers, tenants or a family member arrival against a projected sign-off date. Book them once it is signed off.
What actually shortens it
Three things, in order. Deciding the layout properly before engineering rather than during it. Submitting a genuinely complete application, because an incomplete one does not start the clock. And establishing utility capacity early, because that is the constraint most likely to appear late and least likely to be solvable quickly.
What does not shorten it is pressure applied after submittal. By then the schedule belongs to a review queue.
Frequently asked follow-ups
Is the 60-day rule real? +
Yes - California law requires a city to approve or deny a complete ADU application within a 60-day statutory window. The words doing the work are "complete application". A submittal that comes back with corrections is not one, which is why real totals run longer than 60 days.
Is a garage conversion faster than a detached ADU? +
Generally yes on construction, because the structure and often the slab already exist. It is not automatically faster overall - the question of whether the existing structure can carry the new use can add investigation at the front that a new build does not have.
What is the single most common cause of delay? +
Changing the design after engineering has started. It restarts work that was already done, and on an ADU that work is structural and utility-related rather than cosmetic, so it is not a quick revision.
Can I live in the main house throughout? +
For a detached unit, usually yes - the work is happening outside the house rather than through it. A garage conversion attached to the house is more disruptive, and utility connection days will affect the main house whichever route you take.
Have you built ADUs? +
We have no completed ADU or garage-conversion project with a published final cost, and we would rather say that plainly than imply otherwise. This page is written as process and Los Angeles market knowledge, which is what it is.
Want the same answer applied to your specific project? Onn personally reviews every inquiry.
Written by Onn Cohen-Meguri, founder and designer at Design Onn Point. Onn has spent 20+ years designing and building in Los Angeles. CSLB #1133368.
Published .