Now covered in more depth
Planning a home addition in Seattle but not sure what to budget? This guide walks you through the cost components so you can build a realistic estimate before meeting with an architect or contractor.
Base Cost by Addition Type (Seattle 2026)
| Addition Type | Cost Range / Sq Ft | Typical Total |
|---|---|---|
| Ground floor addition | $350 to $550 | $105K, $275K |
| Second story (partial) | $400 to $600 | $200K, $450K |
| Second story (full floor) | $450 to $650 | $350K, $600K+ |
| Primary suite addition | $400 to $600 | $160K, $280K |
| Kitchen addition | $450 to $650 | $110K, $200K |
What Drives Costs Up
- Structural complexity, load-bearing changes, hillside sites, weak existing foundation
- High-end finishes, custom cabinetry, stone, imported tile
- Tight site access, difficult delivery and staging increases labor cost
- Permits and fees, typically 1.5-2.5% of project cost in Seattle
- Geotechnical issues, poor soils, high water table, landslide-prone areas
Planning a project?
Want a number for your addition?
Send David the address and a few lines about what you want. The first feasibility check is free and usually takes about a day: what the site and the code are likely to allow, and what to check first.
Architect since 1996, member of the AIA and NCARB. Three Masonry Excellence Awards for commercial projects; the Carr residence was featured in Above The Lake and Lux magazines.
What Drives Costs Down
- Simple rectangular footprint
- Good site access
- Standard finishes and materials
- An easy jurisdiction to permit in, which shows up in time rather than in the per square foot rate
Professional Fees to Add to Your Budget
- Architect: 8 to 15% of construction cost
- Structural engineer: $4,000-$12,000
- Seattle permit fees: 1.5-2.5% of project valuation
- Contingency: 15% minimum for renovation projects
Piper Cole Architects provides detailed cost estimates in free initial consultations. See our home additions service or contact us, call 425-753-6452.
