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.
📄 Table of Contents
Base Cost by Addition Type (Seattle 2026)
| Addition Type | Cost Range / Sq Ft | Typical Total |
|---|---|---|
| Ground floor addition | $350 – $550 | $105K – $275K |
| Second story (partial) | $400 – $600 | $200K – $450K |
| Second story (full floor) | $450 – $650 | $350K – $600K+ |
| Primary suite addition | $400 – $600 | $160K – $280K |
| Kitchen addition | $450 – $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
What Drives Costs Down
- Simple rectangular footprint
- Good site access
- Standard finishes and materials
- Eastside jurisdictions (often 10-15% lower labor cost than Seattle proper)
Professional Fees to Add to Your Budget
- Architect: 10-15% 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.
Ready to talk about your project?
Piper Cole Architects has designed 800+ Eastside projects since 2000. Get a free, no-pressure consultation with David Meade, AIA, NCARB.