Permits

ADU Permit Timeline: A State-Agnostic Walkthrough of How Long This Actually Takes

Permits are the part of an ADU build where homeowners burn the most time and the least money. The construction work, once it starts, runs on a schedule a contractor can hold to within a few weeks. The permit work runs on the schedule of whoever-at-City-Hall is reviewing your file this month, and that’s not a number anyone can quote you up front.

So instead of pretending there’s a single answer, here’s the actual sequence: five phases, what happens in each, and what makes each one slower or faster. The honest end-to-end calendar, from “we want to do this” to “we move in,” is about 9 to 14 months in 2026 for most US homeowners. A clean project in a state with strong ADU legislation can finish in 7. A messy project in a slow city can stretch past 18.

This article is state-agnostic. The phases are the same in every US jurisdiction. The durations of each phase shift with your state’s law and your city’s processing capacity. Where state-level differences matter, we flag them.

Phase 1: Pre-application research and feasibility (4-12 weeks)

Before you submit anything, you need to know what’s allowed on your lot. Most homeowners skip this and start with an architect, which is the wrong order. The architect can’t draw a building that needs zoning information you haven’t gathered yet.

The work in this phase:

  1. Pull your lot’s zoning record from the city’s planning portal. This tells you the zoning district (R-1, R-2, etc.) and links to the relevant chapter of the municipal code. Most cities have this online; some require a phone call to planning.

  2. Read the ADU ordinance for your city. Every city that allows ADUs has one. It tells you the maximum size, height, setback, parking, and owner-occupancy rules that apply. (In states with strong ADU legislation, namely California, Oregon, Washington, Vermont, Maine, Massachusetts, and Montana, the state law often pre-empts more restrictive local rules. The state law is the floor; the city ordinance is sometimes more permissive, never less.)

  3. Confirm utility availability. Call your water/sewer utility to confirm whether your line has capacity for a second unit and what their connection fee schedule is. Call your electric utility to confirm whether a second meter is allowed and what panel-upgrade requirements exist. These calls take 30 minutes each and they save months later.

  4. Check for HOA, deed restrictions, or historic-district overlays. Some HOAs prohibit ADUs outright; some require their own architectural review. Historic-district designations layer an additional review on top of the city permit. Both add weeks-to-months of process you have to plan for.

  5. Decide go/no-go. Roughly one in five homeowners who get this far decide their lot or budget doesn’t actually support an ADU. Better to find out now than after $14k of architectural drawings.

This phase takes 4 weeks if you’re efficient about the calls and your jurisdiction’s documents are well-organized online. It takes 12 weeks if you have to make multiple appointments, your HOA needs a board meeting, or your municipal code is a pre-2010 PDF that doesn’t search well.

Phase 2: Plan preparation (8-16 weeks)

Once you know what’s allowed, you hire an architect or designer to draw the plans. Plans for a permit submission are more detailed than a marketing rendering. They include foundation plans, framing plans, electrical and plumbing schematics, energy-code calculations (Title 24 in California, similar in most states), structural engineering for the foundation and lateral systems, and a site plan showing setbacks, drainage, and utility runs.

Architectural design itself is 4-8 weeks for a 600-sq-ft ADU. Add 2-4 weeks for structural engineering, which is usually subcontracted by the architect. Add 1-2 weeks for energy-code calculations and Title 24 (or your state’s equivalent).

The bottleneck in this phase is revisions. Most plans go through 2-4 revision cycles between you, the architect, and any pre-application feedback the planning department gave you. If you’re decisive about the design, this is fast. If you’re not, and most homeowners aren’t because this is the first time they’ve designed a building, it can drag.

A practical tip: ask your architect to set a “design freeze” date and stick to it. Once plans go to permit submission, every change is more expensive than it was before submission. Get to a design that’s 90% of what you want and submit. The 10% you’d have changed isn’t usually worth the time and revision cost.

Phase 3: Permit submission and plan check (6-20 weeks)

You file the plans with the city. The city assigns plan checkers from each relevant department: building, planning, fire, public works, and sometimes others. Each checker reviews their part and produces “comments” (a list of corrections you have to make and re-submit).

This is the phase that varies most across jurisdictions, because plan-check turnaround depends entirely on the city’s processing capacity.

  • Cities with strong ADU streamlining: First plan-check round in 4-8 weeks. Typical of California cities post-SB-9 (60-day statutory window for ADU plan check), Oregon cities under HB-2001, and Washington cities under HB-1337. (California’s ADU laws cap ministerial review at 60 days; if the city blows the deadline, the application is deemed approved by default. Oregon and Washington have similar timing rules. Source: California Government Code §65852.2; Oregon Senate Bill 1051; Washington House Bill 1337.)
  • Mid-tier cities: First plan-check round in 8-12 weeks.
  • Slow cities: First plan-check round in 12-20 weeks. Usually older cities with limited planning staff, or smaller jurisdictions where ADUs are still a rare submission.

Almost every plan-check returns with comments. Common ones:

  • Setback or height not exactly compliant with zoning (architect missed a sub-rule).
  • Energy code calculations need revision (the building department’s reviewer interprets a code section differently from your engineer).
  • Fire department wants additional separation, sprinklers, or access modifications.
  • Public works wants a different sewer connection point or stormwater detention you didn’t plan for.

Your architect responds to comments, makes the revisions, and re-submits. The city reviews the revisions. Typical projects go through 1-3 comment cycles.

Total for Phase 3: 6 weeks for a clean submission in a fast city, 20 weeks for a comment-heavy submission in a slow city.

Phase 4: Permit issuance and pre-construction (2-6 weeks)

Once plan check is approved, you pay the permit fees and the city issues the permits (building, electrical, plumbing, mechanical, usually issued together for an ADU). You sign your contractor’s contract if you haven’t already, and they begin scheduling subs and ordering materials.

In well-organized cities, permit issuance is a same-day event once you pay. In some cities it’s 2-4 weeks of back-and-forth between the cashier, the permit clerk, and the contractor’s license verification.

Material lead times also live in this phase. As of mid-2026, most residential building materials are available within 1-3 weeks; specialty items (custom windows, certain mini-split models, semi-custom cabinets) can run 6-12 weeks. Your contractor will tell you which items need to be ordered immediately and which can wait until the framing is up.

Phase 5: Construction and inspections (16-28 weeks)

This is the part most homeowners think of as “the build.” It’s also the part that runs on the most predictable schedule, because it’s the part your contractor controls.

Standard sequence for a 600-sq-ft detached ADU:

WeekPhase
1-2Site prep, demolition, excavation
3-4Foundation forming, pour, cure
5-9Framing (walls, roof, sheathing)
10-12Roofing, exterior siding, windows, doors
13-15Mechanical, electrical, plumbing rough-in
16-17Insulation
18-20Drywall, tape, texture, paint
21-23Flooring, cabinets, counters, fixtures, trim
24-25Final finishes, landscaping, punch list
26Final inspection, certificate of occupancy

Inspections happen at the end of each major phase: foundation pre-pour, framing, rough MEP, drywall pre-paint, and final. Each inspection is a half-hour visit from a city inspector, and each one has to pass before the next phase can start. A failed inspection adds 3-7 days for corrections and re-inspection. Most projects fail one or two inspections somewhere along the way; that’s normal.

Weather matters. A wet winter in the Pacific Northwest can add 2-4 weeks to foundation and framing. A hot summer in Arizona can slow exterior work in July-August. Build season planning matters. Contractors who push hard to break ground in October are setting you up for a slow February.

The pitfalls that add months

Five things, in order of how often they bite:

  1. Plan check comment cycles you weren’t expecting. Two rounds is the norm. If your architect’s first submission gets four rounds of comments, you’ve added 6-12 weeks. The fix: hire an architect who has done ADUs in your specific city before. They know which reviewers want what.

  2. Discretionary review or design review board. Some cities require an additional review by a design review board on top of normal plan check, especially in historic districts or for ADUs visible from the street. This is its own multi-month process. The fix: confirm during Phase 1 whether your project triggers this.

  3. Utility connection delays. Sewer connection requires a permit from public works that’s separate from your building permit. Electrical service upgrades require coordination with the utility, which has its own scheduling backlog. Both can sit waiting for weeks while construction is otherwise ready to proceed. The fix: file utility permits in parallel with the building permit, not after.

  4. HOA architectural approval. If your HOA has its own architectural review, plan for 30-90 days. Some HOAs only meet quarterly. The fix: check Phase 1.

  5. Contractor scheduling. Good contractors in busy markets are booked 3-9 months out. If you don’t engage one until you have permits in hand, you may wait 6 months for them to start. The fix: select your contractor in Phase 2, sign in Phase 3 contingent on permit, lock the slot.

State legislation that’s taking months back

A handful of states have passed laws in the last few years that materially shortened ADU timelines:

  • California: SB-9, AB-2299, AB-1033, and the broader ADU framework. Ministerial review (no public hearing), statutory 60-day plan-check window, by-right approval if the project meets state standards, impact-fee waivers for units under 750 sq ft. (Source: California Department of Housing and Community Development ADU Handbook, 2024 update.)
  • Oregon: HB-2001 (2019) requires cities over 10,000 population to allow ADUs by right in single-family zones.
  • Washington: HB-1337 (2023) requires cities to allow up to two ADUs on single-family lots, prohibits owner-occupancy requirements, and limits parking requirements.
  • Vermont, Maine, Massachusetts, Montana: all have passed similar laws between 2022 and 2025, with varying scope.

If you’re in one of these states, your timeline is closer to the fast end of every range in this article. If you’re not (most of the South, Midwest, and parts of the Mountain West), you’re looking at the middle to slow end.

The honest end-to-end picture

Adding it up, for a typical homeowner in a typical US city in 2026:

  • Phase 1 (research): 6 weeks
  • Phase 2 (plan prep): 12 weeks
  • Phase 3 (plan check): 12 weeks
  • Phase 4 (permit issuance + lead time): 4 weeks
  • Phase 5 (construction): 22 weeks

Total: about 56 weeks. Call it 13 months.

The fast version of the same project, in a strong-legislation state with a clean lot and a decisive homeowner: 7-8 months. The slow version, in a comment-heavy city with HOA review and material delays: 16-18 months.

The single biggest accelerator isn’t paying for expedited review (most cities don’t offer it). It’s running phases in parallel where the law allows. Phase 1 research can happen while you’re interviewing architects. Plan preparation and contractor selection should overlap. Material ordering happens during plan check, not after. The 13-month figure assumes some parallelism. Sequential, every phase done in turn, the same project takes 18 months.

What to do this week

If you’re at the start of this process:

  1. Pull up your city’s ADU ordinance. Read it through once. (Yes, the actual text, not somebody’s summary.)
  2. Call your water/sewer utility and your electric utility. Ask the connection-fee questions.
  3. Walk your lot with a tape measure. Confirm the setbacks and the buildable area you actually have.
  4. Decide whether your state has strong ADU legislation. If yes, your timeline expectations should sit toward the fast end of the ranges in this article. If no, plan for the middle.

Then start interviewing architects. Phase 2 doesn’t begin until you sign one, and the right architect will save you more time in Phase 3 than they cost in Phase 2.

Where to go next

If your city’s ADU process surprised you in a way this article didn’t capture, the contact link is on every page. We update articles when readers tell us what we missed.