# Building an ADU in 120 Working Days: What Los Angeles Homeowners Should Know *Published 2026-09-25 by 1 Smart Build* Once your permit is issued, we can build an ADU in as few as 120 working days. Here's what makes that timeline possible, what slows it down, and the state rules that can save you money before you break ground. Most homeowners who call us about an ADU ask the same two questions first: how much, and how long. The cost depends on your lot and your plans. The timeline is where we can give you a straighter answer than most people expect. Once your permit is issued, we can complete construction on an ADU in as few as 120 working days. That's roughly 24 weeks of Monday-through-Friday work, or about five and a half months on the calendar. It isn't a promise for every lot. Size, site conditions and finish choices all move the number. But for a well-planned project on a workable site, it's a realistic target, and we plan every ADU around hitting it. This post explains what the 120 days covers, what has to happen before it starts, what speeds it up, what slows it down, and the California rules that now cap fees and approval times. ## Key Takeaways - 1 Smart Build can complete ADU construction in as few as 120 working days once the building permit is issued, depending on size, site conditions and finishes. - Including design and permitting, most Los Angeles ADUs take 8 to 14 months from the first site visit to final inspection. - Under California ADU law, an ADU with 750 square feet or less of interior living space pays no impact fees to the city, special districts or water companies. - ADUs and junior ADUs under 500 square feet of interior living space are also exempt from school impact fees. - Once an ADU application is complete, the city has 60 days to approve or deny it. ## What "120 Working Days" Actually Covers The 120-day clock starts when the permit is in hand and crews can legally start work. It runs through the build itself: site prep, foundation, framing, rough plumbing and electrical, inspections, insulation, drywall, finishes and the final inspection. It does not include design or plan check. Those happen first, and they're where most ADU schedules actually get lost. A typical breakdown looks like this: - **Site visit and feasibility:** 1 to 2 weeks to confirm setbacks, utilities, panel capacity and fire zone. - **Design and engineered plans:** about 4 to 6 weeks. - **Plan check and corrections:** 6 to 16 weeks, depending on the city and how complete the submittal is. - **Construction:** as few as 120 working days after the permit is issued. Working days means business days. Weekends and holidays aren't counted, and neither are days lost to heavy rain when concrete or roofing can't go in. ## Why We Can Build That Fast Speed on an ADU doesn't come from rushing the crew. It comes from removing the waiting. Most of the time lost on a typical build is time spent waiting on a decision, a delivery or an inspection. Here's how we cut that down. ### The plans are complete before they go to the city Incomplete submittals get sent back with corrections, and each round adds weeks. Because we design and build, the people drawing your plans are the same people who have to build from them. We catch conflicts between structural, plumbing and electrical before the city does. ### Selections get locked early Windows, doors, cabinets and tile often have lead times of several weeks. We finalize your selections while the plans are still in plan check, so materials are ordered before the permit is issued and arrive when the crew is ready for them. ### One team runs the whole job You aren't coordinating an architect, an expediter and a separate builder. One project manager owns the schedule, books the inspections ahead of time, and keeps trades moving in sequence instead of leaving gaps between them. ### You can see where things stand Every client gets a private portal with the schedule, milestone payments, approvals and job-site photos. When a decision is needed from you, you see it right away instead of finding out a week later. ## What Can Stretch the Timeline We'd rather tell you now than surprise you later. These are the most common reasons an ADU build runs past 120 working days: - **Hillside or difficult sites:** soils reports, deeper foundations, retaining walls and limited equipment access all add time. - **Utility upgrades:** a new electrical service, a panel upgrade that needs the utility company, or a new sewer connection can depend on outside schedules. - **Larger units:** a 1,200-square-foot two-bedroom takes longer than a 500-square-foot studio. - **Custom finishes:** special-order materials with long lead times. - **Changes after construction starts:** moving a wall or a window mid-build means revised plans and sometimes a new inspection. - **Weather:** heavy rain can pause foundation and roofing work. We look at all of this at the first site visit and give you a schedule based on your actual property, not a best-case guess. ## 2026 California Rules That Help Before You Break Ground State law has made ADUs cheaper and more predictable to permit. According to the [California Department of Housing and Community Development's March 2026 ADU Handbook](https://www.hcd.ca.gov/sites/default/files/docs/policy-and-research/adu-handbook-update.pdf), here's what applies: ### No impact fees at 750 square feet or less If your ADU has 750 square feet or less of interior living space, the city, special districts and water companies can't charge impact fees on it. Above 750 square feet, impact fees have to be proportional to the size of your main home. ### No school fees under 500 square feet ADUs and junior ADUs under 500 square feet of interior living space aren't subject to school impact fees. For some homeowners, that alone makes a smaller unit the smarter choice. ### A 60-day decision on complete applications Once your application is complete, the city has 60 days to approve or deny it. That's why a complete, well-checked submittal matters so much. The clock only starts once the city considers the application complete. Keep in mind that building permit fees, plan check fees and utility connection fees can still apply. We confirm the exact fees for your city before design is finished. You can also read general ADU guidance on the [HCD ADU page](https://www.hcd.ca.gov/policy-and-research/accessory-dwelling-units) and permit information on the [LADBS website](https://www.ladbs.org/). ## Picking the Right Size for Speed and Cost If a fast timeline and lower fees matter most to you, size is the biggest lever you control: - **Under 500 sq ft:** no impact fees and no school fees. A studio or compact one-bedroom, usually the quickest to build. - **500 to 750 sq ft:** no impact fees, school fees may apply. A comfortable one-bedroom for a renter or family member. - **Over 750 sq ft:** proportional impact fees apply. Two-bedroom units with more room, and usually a longer build. Garage conversions can move even faster because the slab, walls and roof are already there, as long as the slab and ceiling height check out. ## How to Check Your Contractor A fast timeline only matters if the work is permitted and done right. Before you sign with anyone, look up their license on the [Contractors State License Board](https://www.cslb.ca.gov/) site. 1 Smart Build Inc. holds CSLB license #1076428 (Class B, General Building Contractor). Ask any contractor what their construction timeline covers, when the clock starts, and what they do when a delay comes up. ## Start With a Free Site Visit Every ADU schedule starts with the lot. We'll walk your property, tell you what's buildable, flag anything that could slow the build, and give you a realistic timeline and fixed-price proposal. You can also run a quick check on your property with our [free build check](/build-check), or read more about our [ADU and garage conversion services](/services/adu-garage-conversion). Call 1 (866) 419-8840 to schedule your free consultation. ## Company facts - Business: 1 Smart Build, design-build general contractor - Phone: 1 (866) 419-8840 - Email: info@1smart.build - Office: 21243 Ventura Blvd #133, Woodland Hills, CA 91364 - License: California CSLB #1076428 (Class B, General Building Contractor) - Insurance & bond: $1,000,000 liability policy, $15,000 contractor bond - Reviews: 4.9 stars on Google (162 reviews) - Ownership: Veteran-owned and women-owned - Service area: Los Angeles County and the San Fernando Valley Canonical HTML version: https://1smart.build/blog/adu-construction-120-working-days-los-angeles Site index for agents: https://1smart.build/llms.txt