How Long Does It Take to Build a DADU in Seattle?
By Eric Dexter, Owner & Builder ·
From the first call to move-in, a DADU in the Seattle area typically takes about 12 to 18 months. Most of that isn't swinging hammers — it's the design and permitting that happen before construction starts. Here's a realistic breakdown.
The realistic DADU timeline
Feasibility & design — about 1–3 months
First you confirm what your lot allows and design the unit. Starting with a feasibility study here saves time later by catching zoning, setback and site issues before they become expensive surprises.
Permitting — about 2–6 months
Once drawings are done, the permit application goes into review. This is the least predictable phase because review times vary by jurisdiction and workload. A complete, well-prepared application moves faster; see our DADU permit guide for what's involved.
Construction — about 6–9 months
With permits in hand, the build runs from site work and foundation through framing, systems and finishes. A clean, simple lot moves faster than one with critical areas or complex utilities.
What slows a project down
- Difficult lots — slopes, Environmental Critical Areas, long utility runs
- Permit backlogs in a busy jurisdiction
- Mid-project design changes
- Financing that isn’t lined up before you start
What speeds it up
- A feasibility study first, so the budget and design are built on facts
- Starting from proven ready-to-build floor plans
- One team that self-performs site work through finishes — fewer handoffs
- Decisions and financing settled early
Plan the timeline with us
Every lot is different, so the best way to get a real schedule is to walk your project with a builder. See how our process works, estimate the build with the cost calculator, or get in touch for a realistic timeline on your lot.
