How long does it take to build an ADU? (2026 San Diego timeline)

How long does it take to build an ADU?

No public agency tracks ADU projects from start to finish, so total-project figures come from builders. Their published ranges line up reasonably well. Snap ADU's San Diego timeline guide puts the whole process at 10 to 18 months or more. Maxable's guide says 12 to 18 months. And Snap ADU's 2026 report on 100 completed builds says detached ADUs in San Diego “routinely take 12 to 24 months from concept to completion.”

The legal clocks come from Government Code § 66317 and the utility range from SDG&E's April 2026 service estimates. The design and construction ranges are builders' own figures, not guarantees. This guide covers how long each phase takes; for what actually happens on site in each one, see the ADU construction process, and for the decisions you make before any of it starts, read how to build an ADU.

Design: 6 weeks to 4 months

Design is the phase you control most. It covers a site survey if your lot needs one, the floor plan, structural engineering, Title 24 energy calculations and the full permit set. Maxable puts it at 6 weeks to 3 months before submission; Snap ADU says two to four months.

What pushes design toward the long end:

• Changing your mind. Every layout change after engineering starts means new structural and energy work.
• Site questions. Slopes, easements, sewer lines and fire-zone rules need answers before the plans can be finished. Snap ADU's 2026 report says waiting until plan check to deal with them “often means redesign, reengineering, and months of lost time.”
• Financing. If you need a loan, it runs alongside design. Maxable estimates 60 to 90 days to fund one. See ADU financing for the options.

Who draws your plans also shapes the schedule. Compare the trade-offs in design-build vs an architect, or read what an ADU architect does and costs.

ADU permit timeline

This is the only phase with deadlines written into law. Under Government Code § 66317, a city or county must:

• Check completeness within 15 business days. If the application is incomplete, the written notice must list what's missing and how to fix it. If the city misses the deadline, the application is deemed complete.
• Approve or deny within 60 days of a complete application, if there's an existing house on the lot. If it does neither, the permit is deemed approved. A denial must come with a full set of comments listing what's deficient and how to remedy it.
• Offer an appeal of an incompleteness finding or a denial, with a final written decision within 60 business days of the appeal.

Two details from the state's ADU handbook matter for your schedule. You can ask the city to pause the 60-day clock for any reason, and the clock is tolled while it's paused, which is common while you revise plans. And if you're tearing down a detached garage to build the ADU, the city must review and issue the demolition permit at the same time as the ADU permit. A detached ADU built from a pre-approved plan gets a shorter clock: 30 days to approve or deny.

How long to get an ADU permit in San Diego

On paper, 15 business days plus 60 days is about three months. In practice the total depends on how many correction rounds your plans need. The City of San Diego describes the loop on its permit timeline page: staff screen your upload for completeness and set fees; once you pay, the project goes into a review queue for each discipline. Each reviewer issues a cycle issues report, and you can't upload corrections until every discipline has finished its cycle. Your responses then go back as a single consolidated package.

The city publishes how fast each round goes. In its fiscal 2027 draft budget, Development Services reports:

These cover all building construction, not ADUs alone. The takeaway: a single review cycle is now short, but more than half of applications aren't complete the first time, and each round of corrections adds your designer's response time plus another review cycle. Snap ADU says it always sees second-round reviews on ADU plans and puts the full permitting phase at three to nine months. The permit timeline page also posts a weekly snapshot of intake, review and issuance times; on October 23, 2026, issuing a building permit after approval took about one business day.

Once the permit is issued, the clock runs the other way. Under the city's municipal code, a building permit becomes void if substantial work hasn't been completed and passed an inspection within 12 months of issuance, or if work stops for 180 days, unless you get an extension. The permit itself expires three or four years after issuance depending on the building type, and an application that's deemed complete but never issued is closed after two years. Our guide to getting an ADU permit in San Diego covers what to submit and the fees.

Utility hookups and SDG&E

If your ADU runs off the main house's electrical service, the utility work is part of construction. If you need a separate meter or a bigger service from SDG&E, you join the utility's queue, and it can be the slowest part of the job. SDG&E's own estimates, based on historical projects:

SDG&E calls these planning estimates, not commitments, and lists service distance, underground work, equipment availability and weather among the things that move them. Two steps come before the clock starts. For an ADU, you need an address from the city before you apply, and SDG&E asks you to allow two weeks for it to review the application. Apply as soon as your plans and load calculations are final, not when the walls go up.

Utility work can also hide delays at the street. Lars Remodel's cost guide recounts a 2021 San Diego Housing Commission pilot site that took more than six months of added work to split utilities through street trenching. A separate SDG&E meter also costs money: Snap ADU estimates $10,500 to $15,000. Our ADU utilities guide explains when a separate meter, panel upgrade or sewer pump is worth it.

Construction: 5 to 8 months

For a site-built detached ADU, builders publish similar ranges. Snap ADU says construction “typically takes five to seven months,” with two-story and larger units taking longer. Maxable says 5 to 8 months. Within that, the work runs in a fixed order: site prep and trenching, foundation, framing and rough plumbing and electrical, insulation, drywall, then finishes. Each step waits on an inspection before the next can cover it up.

What stretches construction:

• The lot. Slopes, poor soil, retaining walls and tight access add weeks of site work before the foundation.
• Size and stories. A two-story ADU adds framing, a stair and more inspections.
• Materials. Windows, cabinets and custom finishes with long lead times should be ordered before you need them.
• Weather and inspection queues. Both are on Snap ADU's list of construction delays.
• The contractor's workload. A crew spread across too many jobs leaves gaps between trades. That's worth asking about before you sign; see how to hire an ADU contractor.

Inspections and move-in

City inspectors sign off each stage before it's concealed. The City of San Diego's list of inspection types runs from underground and foundation through framing, insulation and drywall to the final, and the final inspection is the approval to occupy. Standard inspections must be booked at least one day ahead and happen on weekdays between 8:30 a.m. and 3:30 p.m. The city reported completing 91% of scheduled building inspections by their target date in fiscal 2026.

A failed inspection costs you the fix plus a re-inspection, and the next trade can't start until it passes. Under state ADU law, you need a certificate of occupancy before anyone lives in the unit, so don't sign a lease or book a move until the final is approved.

What causes ADU delays

Most delays trace back to a handful of causes, and most of them start before construction:

• An incomplete first submittal. Only 44% of applications to the City of San Diego were complete on first submittal in fiscal 2026. Each extra intake screen or correction round adds weeks.
• Site rules found late. Snap ADU's 2026 report says fire hose pull distances, brush management, survey requirements and sewer easement setbacks are being enforced more strictly, especially in the City of San Diego.
• Coastal review. In the coastal zone you may need a coastal development permit as well. The HCD handbook says it must be decided within 60 days of a complete application, alongside the ADU permit, but it's one more application to get complete.
• Utility service. SDG&E's estimates run up to 266 days for new electric service to an ADU.
• Redesign. Changes after plan check restart engineering and review.
• Money. A loan that funds late, or a budget that comes in short after bids, stalls a project between phases.
• Your builder. A contractor who stops work or goes under can cost months, and a stalled job risks the permit lapsing. Compare verified ADU builders in San Diego and check a contractor's license before you sign.

Ways to shorten the timeline

• Use a pre-approved plan. The City of San Diego gives a 30-day review to applications using County of San Diego, Chula Vista or Encinitas pre-approved plans. The County's free plans come in 600, 800, 1,000 and 1,200 sq ft versions and are about 85% complete, so you still need a site plan. See pre-approved ADU plans in San Diego.
• Submit a complete package. Hire a designer who has recently permitted ADUs in your city and ask how many correction rounds their last few projects took.
• Overlap phases. Apply to SDG&E, line up financing and order long-lead items while the permit is in review.
• Consider prefab, with eyes open. Snap ADU's October 2026 prefab guide cites factory build times of 4 to 6 months after permits and installation in days to weeks, but says the overall timeline is “typically about the same” as stick-built. See prefab ADUs in California.
• Convert instead of building new. A garage conversion or junior ADU reuses an existing foundation and walls, which removes the earliest construction stages.

Time is also money: rent, loan interest and carrying costs keep running while you wait. Budget for the schedule as well as the build with our guide to what an ADU costs in San Diego, and read California ADU laws for the rules behind the permit clock.

Common questions