Ask anyone who has tried to build an ADU what surprised them most, and the answer is almost always the same: It took way longer than I thought it would.
So how long does it take to build an ADU? On paper, the numbers look simple. A garage conversion in three months. A detached accessory dwelling unit in four or five. Maybe half a year for something larger.
Yet project after project drifts past those timelines, eight months, a year, sometimes longer. And here is the part that catches homeowners off guard: the delay usually has nothing to do with construction.
Permits drag on. Decisions stall. Utility hookups get complicated. By the time a crew is ready to start building an ADU, weeks or months may already be gone.
This is the real reason ADU construction timelines stretch out, and the part most homeowners never see coming. Insights from Quality First Builders, a leading remodeling firm in Los Angeles based in Sherman Oaks, contribute to this perspective, drawing on their experience managing ADU projects across the city.
Permitting is the silent timeline killer. On paper, it looks like a formality: you submit plans, the city reviews them, you get approval, and off you go. In reality, this step can stretch for weeks or even months.
How long does it take to get permits for an accessory dwelling unit in California? That depends on where you live. Los Angeles city is usually one of the faster jurisdictions, while Pasadena, Glendale, Santa Monica, and Burbank often take much longer. A permit that moves in four weeks in one city can take twelve in another.
And it is not just the city. Many delays come from the plans themselves. A missing dimension, an unfinished detail, a placeholder that says “TBD” — each one triggers a resubmittal. What should be a two-week check turns into six.
The fastest way through permitting is submitting a complete, clean set of plans the first time. The slower way — and the one that drags projects past their expected ADU construction timeline — is waiting for the city to send your drawings back again and again.
One of the least obvious reasons building an ADU takes longer than expected is hesitation. Homeowners wait to pick cabinets. They change their mind on tile. They go back and forth on fixtures. Each pause pushes the schedule out.
Construction crews cannot move without answers. Plumbing rough-ins cannot be finished until fixtures are locked in. Electrical cannot be signed off until outlet placements are confirmed. Inspectors cannot approve a phase when key details are missing.
It does not always feel like much in the moment: a week to pick tile, two weeks debating countertops. Add those delays together and you can lose a month or more.
Projects that move quickly are not always the ones with the biggest crews. They are the ones where decisions were made up front, nothing was left floating, and every choice was finalized before building an accessory dwelling unit began.
Utility hookups look simple on paper — a line for water, a line for sewer, gas, and electrical. In practice, this is one of the most common places a project hits pause.
Shared meters are usually the fastest route: tie the ADU into the main home and you are done. But if you decide on separate meters, the timeline stretches. That means trenching all the way to the street, new applications with utility providers, and waiting for inspections that can take weeks to book.
Even when you stick with shared utilities, things can drag. A tight backyard may force crews to trench by hand. A slope can trigger grading work. Sometimes the issue is as simple as waiting for an inspector from the power company.
These delays do not always look dramatic, but they stack. An extra week here, two weeks there. Before you know it, the ADU in Los Angeles or any California city that was supposed to be moving fast is crawling.
Not every property is a blank slate. Some lots carry extra rules that add time before a single wall goes up.
Hillside parcels often need geotechnical reports to confirm stability. Coastal areas can trigger environmental reviews that move at their own pace. Homes in historic zones may be required to pass architectural review to make sure the new dwelling unit fits the neighborhood.
None of this makes an ADU impossible. It just means the path is slower. Reviews from multiple departments, additional reports, and back-and-forth between agencies can easily tack on weeks or even months.
Most homeowners do not realize their property has these restrictions until plans are already submitted. At that point, the only option is to wait. The best way to keep an ADU timeline under control is to work with a builder who knows how to spot these issues before the city does.
By the time the plans are approved and the decisions are made, construction is usually the part that runs closest to schedule. Crews know what to build, inspectors know what to check, and the process has a clear rhythm.
So how long does it take to build an ADU once construction starts? A garage conversion often wraps in about three months. A detached single-story accessory dwelling unit takes four to five months. Two-story ADUs can push five or six months. Those numbers hold as long as the earlier phases were handled cleanly.
When projects drag far past those averages, it is rarely because a carpenter is working too slowly. It is almost always because the job was stalled long before the first wall went up.
Most homeowners blame contractors when an ADU project drifts. In reality, the real reason an ADU timeline gets delayed almost always comes down to permits, indecision, or utility complications.
The good news is that these delays are predictable. When finishes are chosen up front, when plans are complete before submission, when utility strategies are clear from the start, the build moves at the pace it should.
Construction itself is rarely the problem. It is the preparation that makes or breaks the schedule.
Quality First Builders has guided countless homeowners through the ADU construction process with timelines that stay realistic and predictable. With the right planning, your accessory dwelling unit can be built in months, not years, and without the frustration of endless waiting.