Many owners want a firm date for when they can start building. A move, a lease or a loan may depend on it. The DADU permit timeline rarely works that way, because it moves in phases that depend on your site, your team and the city’s workload.

This guide breaks the process into separate stages and explains what affects each one. It avoids promising durations, since no honest source can guarantee them.

Why the DADU Permit Timeline Varies

Every project carries its own mix of conditions. A simple lot with a preapproved design moves differently than a sloped lot with large trees and a custom plan. In addition, each round of corrections adds time on both the city’s side and the applicant’s side.

City workload also matters. SDCI explains that its target review dates assume typical demand. When volume runs high compared to staffing, the department says it may miss those targets.

Preparation Before You Apply

The first phase happens before the city sees anything. It includes design, surveys, engineering and gathering records. It also includes the online pre application, where SDCI confirms the legal description and address and may ask for a site visit.

This phase often takes longer than owners expect. For example, a survey, a soils report or an arborist report can each add a step. Tree questions in particular can reshape a footprint, as our guide to Seattle DADU trees explains. Our guide to DADU design cost explains why careful design work pays off later.

Intake and Acceptance

Next comes the intake appointment. The applicant uploads the full plan set and forms, and the city checks that the package is complete. If key items are missing, SDCI will not accept the application.

Appointment availability changes over time. According to the city’s ADU guide, the next opening can sometimes sit months out. However, an applicant who schedules intake and uploads complete materials joins an express lane and hears about earlier openings.

Review Cycles in the DADU Permit Timeline

After intake, several city teams review the plans. Most permits then go through more than one cycle. The city issues a correction notice, the applicant revises and resubmits, and the cycle repeats until every issue resolves.

Each cycle has two clocks. One counts the days the city holds the file, and the other counts the days the applicant holds it. Our post on ADU permit corrections explains how to shorten the applicant side.

Reviews also follow a queue. SDCI assigns plans to reviewers in order, often close to the target date. So a review that shows as pending in the portal does not always signal a problem.

Revisions and Issuance

Revisions take real design time. A small comment may need one note, while a site conflict may need a redesign of part of the cottage. So the length of this phase depends heavily on what the reviewers find.

Once all reviews pass and fees clear, SDCI issues the permit. Even then, other approvals may follow, and construction brings its own series of inspections. For instance, a new construction side sewer permit from Seattle Public Utilities cannot issue until the construction permit does.

What the City’s Data Actually Measures

SDCI publishes permit data on its construction permit performance page. The data runs from intake, when the city accepts an application, to issuance.

• Total calendar days. This measure includes city time and applicant time.
• Days in city control. This measure counts only the days the city holds the file.
• Median. Half of permits take less time and half take more.
• High percentile. Most permits finish within this value, while some take longer.

The city also notes that the total time an applicant experiences runs roughly double the days in city control. Because of that, a goal for city time does not equal a start date for construction.

The data also splits projects into groups. Houses with accessory units fall under a middle housing group, while projects that use the city’s preapproved cottage plans have their own group. As a result, the right comparison depends on the path your project takes.

Why Old Averages Are Not Guarantees

Older articles often quote a fixed number of weeks or months. Some city pages also include duration estimates from earlier years. Those figures describe past permits under past workloads, rules and staffing.

Conditions keep changing. For example, the city set new permit goals as of October 1, 2025, and keeps updating its data. An average also hides the spread, so your project could land well above or below it. Therefore, treat any published figure as context rather than a promise.

Planning Around the DADU Permit Timeline

A few habits help owners plan with less stress. First, build flexibility into decisions that depend on the start date, such as a lease ending or a family move. Then keep a cash buffer, since delays can affect costs, as our guide to the DADU contingency budget explains.

Talk with your design team about the phases that apply to your lot. Ask which steps they expect to take the longest and why. Also, track your own permit in the city’s Construction Permit Timeline tool. It shows which reviews have finished and when the file moved between the city and the applicant.

Keep notes as you go. A short record of each phase, with dates in your own calendar, helps you see where time went and plan the next step with more confidence.

Overall, the permit process moves through preparation, intake, review, revisions and issuance. Each phase has its own drivers, and current city data remains the best way to judge where your project stands.