How long does it take to get an ADU permit approved? In most jurisdictions, the full process from initial drawing production through final permit issuance typically ranges from two to six months, though this varies considerably based on your specific jurisdiction’s workload, the type of ADU you are building, and, most significantly, how well coordinated your drawing submittal is before it ever reaches a plan reviewer. That range is wide because ADU timelines genuinely depend on a set of variables that generic online searches rarely explain clearly, which is exactly why this question comes up so often during initial consultations.

I understand the frustration behind this question. Many homeowners have read about state legislation designed to streamline ADU approval, and reasonably expect that streamlining to translate into a fast, predictable process. In practice, streamlined legislation typically addresses zoning barriers, like minimum lot size or mandatory public hearings, rather than eliminating the actual technical review your drawings still need to pass, which means the timeline still depends heavily on factors within and outside your control.

After a decade producing ADU permit packages across a wide range of jurisdictions, I want to break down what actually drives ADU permit timelines, what a realistic schedule looks like broken into its real phases, and where I most often see ADU projects lose time that could have been avoided with better upfront preparation.

What Actually Determines ADU Permit Timeline

Jurisdiction Workload and ADU Specific Processing

Some jurisdictions have established dedicated, expedited review tracks specifically for ADUs in response to state streamlining requirements, while others process ADU applications through the same general queue as any other residential permit, meaning your specific jurisdiction’s approach to ADU applications significantly affects your realistic timeline expectations.

ADU Type and Complexity

A garage conversion, a new detached structure, and an attached addition each involve different technical scopes, and this directly affects drawing production time. Garage conversions in particular often require more extensive structural and systems documentation than homeowners initially expect, since converting an unhabitable structure into a dwelling unit involves comprehensive foundation, electrical, plumbing, and energy code documentation.

Utility Infrastructure Requirements

ADUs requiring new utility connections, a new sewer lateral, an electrical panel upgrade, or a new water service line, generally involve additional civil and utility coordination that can extend both drawing production time and the number of departments involved in review.

Existing Conditions Documentation

For garage conversions and attached ADUs in particular, the process typically begins with documenting existing conditions accurately, and projects starting without reliable existing drawings or surveys add meaningful time to the front end of the schedule while this documentation is developed.

Coordination Quality of the Drawing Submittal

This is the single largest controllable factor. ADUs require full architectural, structural, MEP, and often civil documentation despite typically being a smaller structure than a primary residence, which means the coordination between these disciplines carries disproportionate weight relative to the ADU’s size. A well coordinated submittal moves through review with meaningfully fewer correction cycles than one assembled from disconnected consultants.

A Realistic Phase by Phase ADU Timeline Breakdown

Predesign and Regulatory Confirmation

Before drawings begin, confirming your property’s zoning designation, any lot specific restrictions, owner occupancy requirements, and parking requirements specific to ADUs in your jurisdiction typically takes a matter of days to a couple of weeks, and skipping this step is one of the more common ways ADU projects lose time later in the process.

Existing Conditions Documentation

For conversions and attached units, documenting existing conditions, whether through an available survey and as built drawings or a site visit and measurement process, typically adds one to a couple of weeks depending on the availability of reliable existing documentation.

Schematic Design

Initial floor plans and overall unit layout are developed during this phase, allowing you to review and provide feedback on the fundamental design before detailed technical drawings begin, typically taking one to a few weeks depending on how quickly feedback is provided.

Construction Documents and Multi Discipline Coordination

This phase produces the final, fully detailed drawing set across architectural, structural, MEP, and civil disciplines as applicable, with cross discipline coordination confirming every sheet agrees with every other sheet before submittal. This is typically the most time intensive phase, generally taking a few weeks for a coordinated team, and rushing it is one of the more common ways plan check corrections later extend your overall timeline.

Plan Check and Permit Review

Once submitted, jurisdictions typically take anywhere from a few weeks to a couple of months to complete initial review, depending heavily on the specific building department’s current ADU processing approach and workload. Jurisdictions with dedicated ADU review tracks often move faster through this phase than those processing ADU applications through a general queue.

Correction and Resubmittal Cycles

If the plan reviewer issues correction comments, and this happens even for well prepared submittals, addressing them and resubmitting typically adds additional weeks, with the total impact depending heavily on how many correction cycles are required and how promptly the correction response is prepared.

The Insider Reality About What Actually Extends ADU Timelines

Here is something that took years of tracking ADU project timelines to fully appreciate. The number of plan check correction cycles has a far greater impact on total timeline than any single review period, and correction cycles are determined almost entirely by how well coordinated the submitted drawings were, not by the inherent complexity of the ADU itself.

The most common and costly mistake I see is homeowners choosing a drawing team based primarily on the fastest quoted production timeline, without accounting for the reality that a rushed, poorly coordinated set generating two or three rounds of corrections will almost always take longer in total than a properly coordinated set that moves through review with a single minor correction cycle or none at all.

Another frequent issue involves utility infrastructure discoveries made too late in the process. Homeowners who assume their existing electrical panel or sewer connection has adequate capacity for a new dwelling unit, without verifying this during design, sometimes discover mid process that a panel upgrade or new utility connection is required, an unexpected addition that not only affects budget but can meaningfully extend the timeline if it was not identified and documented from the outset.

A third issue worth flagging involves garage conversions specifically, where homeowners sometimes assume the existing structure will meaningfully shorten the design and drawing production timeline, when in practice converting a garage into a fully code compliant dwelling unit often requires comprehensive foundation, insulation, electrical, and plumbing documentation comparable in scope to new construction, meaning the drawing production timeline is often similar to, rather than meaningfully shorter than, a new detached ADU.

A fourth issue involves client decision making speed during schematic design. Projects where the homeowner makes prompt decisions on layout and finish selections move meaningfully faster than projects where feedback is delayed by weeks between each round, since the entire production schedule effectively pauses while awaiting a decision.

How to Protect Your ADU Timeline

Confirm your jurisdiction’s specific ADU regulations and whether a dedicated expedited review track exists, since this significantly affects realistic plan check timeline expectations.

Choose a team that produces architectural, structural, MEP, and civil drawings under one coordinated process, since this consistently reduces the correction cycles that add the most unpredictable time to ADU projects specifically, given how much coordination even a small unit requires.

Verify utility infrastructure capacity, electrical panel and sewer connection in particular, early in the design process rather than assuming adequacy, since this is a common source of unexpected timeline extension.

For garage conversions, set realistic expectations that the drawing production timeline is likely comparable to new construction rather than meaningfully shorter, given the comprehensive systems and structural documentation required.

Commit to prompt decision making during schematic design, since delayed feedback is one of the most common, and most avoidable, sources of extended timelines.

Final Thoughts From the Drafting Table

There is no single honest number for how long an ADU permit takes, because the real answer depends on your jurisdiction’s specific ADU processing approach, the type of unit you are building, and factors within your control like drawing coordination quality and decision making speed. What I can tell you with confidence, after a decade tracking these timelines across a wide range of ADU projects, is that coordination is the single biggest lever available for keeping your project on schedule, since plan check correction cycles, not initial drawing production, are what most often determine whether an ADU moves quickly through approval or stalls for months.

If you want a realistic timeline for your specific ADU project, along with a coordinated architectural, structural, MEP, and civil drawing package designed to move cleanly through plan check, we would be glad to review your property and provide a free quote within twenty four hours.