What Does a Second-Story Addition Cost in the Seattle Area?

On a Kirkland or Bothell rambler with a view, a tight Seattle lot, or anywhere the yard is the best thing about the property, a second story is how a three-bedroom becomes a five-bedroom without losing the garden. It is also the most structurally serious residential project we build, and the price reflects that.

Expect $350 to $550 per square foot of new space around Seattle in 2026, or roughly $300,000 to $550,000 for a full second story of 800 to 1,000 square feet. A partial second story over one wing runs $200,000 to $350,000.

Where the money goes

• Engineering and design ($15k–$40k). Structural engineering, architectural drawings, and an energy-code package. The engineer decides what the existing house can carry.
• Foundation and structure below ($15k–$60k). New pad footings under new posts, sometimes reinforcement of the existing footings, beams through the main floor, and shear walls to resist wind and earthquake load.
• Roof off, roof on ($30k–$60k). Demolition, the temporary weather protection that keeps the house dry while it is open, new framing, and a full new roof. This is where a wet Seattle autumn costs money if the schedule is wrong.
• The stair ($10k–$30k). It takes space from the main floor, usually 40 to 60 square feet, and it decides whether the plan works.
• Systems and finishes. Heating extended or a new zone, a bathroom upstairs, electrical, insulation to current code, windows, siding matched to the existing house, and the finish level.

Up or out?

A ground-level addition runs $250 to $450 per square foot because the existing house does not carry anything new; our home addition cost guide has those numbers. Up wins when the lot has no room, when setbacks and lot coverage block a bump-out, or when the yard matters more than the difference. Sometimes the answer is neither: an attic conversion or a finished basement adds the room for a third of the price if the house already has the volume.

The foundation question

Many 1950s to 1980s ramblers sit on footings sized for one story. That does not rule out a second floor, but it decides the budget. We have the engineer look before anyone draws a floor plan, because a $40,000 foundation surprise belongs in the first conversation. Split-levels are their own case: the half-level gives structure in one wing and none in the other, and partial second stories are common for that reason.

Permits, height and schedule

A second story needs a full building permit with structural and energy sheets, and it has to fit the zone’s height limit, which on some Seattle and Kirkland lots is the real constraint. Our addition permits guide walks through the process, and permit timelines by city shows how long each office takes. Construction is typically six to nine months, with three to five of those out of the house. We schedule the roof-off phase for the drier months whenever the permit allows it.

Making it look like it was always there

The second stories that add value are the ones nobody can spot. Roof pitch and overhangs that match, siding and window profiles carried up from the first floor, and proportions that do not make the house look like a box on a box. That is design work before it is construction work, and it is why we price it alongside the structure rather than as an afterthought. If the existing siding is tired anyway, re-siding the whole house with the addition is often the cleaner answer; see our siding cost guide.

Building up with ENF

Second stories are part of our additions work, most often on Kirkland ramblers and split-levels, in Bothell, and on tight Seattle lots. The first visit includes a look at the foundation and the zone’s height limit, and the estimate prices up and out side by side.

Price a second story →