As we head into 2025/2026, the answer has shifted. Rising material costs, permitting fees, and site complexities mean that accurate, up-to-date information is more important than ever for homeowners planning a project. Here’s what you need to know.
The total cost of a backyard cottage isn’t just about square footage. It includes:
Design & Plans – Architecture, engineering, and site planning.
Permitting & Fees – City of Seattle plan review, inspections, and impact fees.
Construction – Framing, systems, finishes, kitchens, baths, HVAC.
Utilities – Connections to water, sewer, and power.
Landscaping & Site Work – Grading, drainage, patios, walkways.
Contingencies – Unexpected conditions or upgrades during the build.
Because of these variables, smaller units don’t always scale down neatly — a 450 sq ft DADU often has a higher cost per square foot than a 1,000 sq ft build.
Size (Sq. Ft.) | Low Estimate | Typical Range | High Estimate |
450-600 sq ft | $300,000 + | $325,000 - $400,000 | $450,000 |
800 sq ft | $375,000 + | $425,000 –$550,000 | $600,000 |
1,000 sq ft | $450,000 + | $550,000 –$700,000 | $800,000 |
Average 2025/2026 cost per square foot (all-in): $400–$650.
Over the past five years, we’ve delivered nearly 20 backyard homes across Seattle — from Ballard to Beacon Hill. That experience means we understand the quirks of permitting, the realities of Seattle construction costs, and the creative ways to design spaces that feel larger than their footprint.
Homeowners choose us because we don’t just hand over a set of plans — we guide you through the entire process: from design and permitting to final landscaping.
If you’re considering a DADU for rental income, multi-generational living, or simply expanding your home’s footprint, now is a great time to start planning. With design, permitting, and construction timelines, projects that begin in 2025 will likely finish in 2026.
Let’s talk about your lot, your goals, and your budget. With nearly 20 DADUs built since 2020, we’d love to bring our experience to your backyard.