Cost to Add a Second Story in Seattle (2026): Complete Budget Breakdown

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.

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 (10 to 15% of construction)
• Structural engineer: $5,000 to $12,000
• Seattle permit fees: $5,000 to $15,000