How Long Does It Take to Build a DADU in Seattle?

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.