Now covered in more depth
Adding a second story is one of the most effective ways to nearly double the living space of a Seattle home without consuming any yard. It is also one of the more complex and expensive addition types. Here is a realistic 2026 cost breakdown.
Second Story Addition Cost Per Square Foot
In the Seattle area in 2026, second story additions run $400 to $700 per square foot of new space. A full 1,000 sq ft second story typically costs $400,000 to $700,000. This is higher than ground-level additions because of the structural work required.
What Drives the Cost
Foundation reinforcement:
The existing foundation must support the new load. Reinforcement adds $20,000 to $60,000.
Structural strengthening:
Existing walls may need reinforcement to carry the second floor.
Temporary relocation:
The roof is removed during construction, so the home is exposed. Most families relocate for 4 to 8 months.
New stairway:
Interior space must be reconfigured to add stairs, reducing usable first floor area.
Roof replacement:
The entire roof is rebuilt.
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.
Partial vs. Full Second Story
A partial second story (adding over part of the home, such as the garage or one wing) costs less and may avoid relocating. A full second story maximizes added space but is more disruptive.
Architect and Permit Costs
- Architect fees: $35,000 to $90,000 (8% to 15% of construction)
- Structural engineer: $5,000 to $12,000
- Seattle permit fees: $5,000 to $15,000
