Second-Story Additions in Bellevue & the Eastside
A second-story addition removes the roof of a one-story house and builds a new floor on top, usually adding bedrooms and a bathroom without using yard space. It suits ramblers on lots with no coverage left. On the Eastside a full second story typically costs $420,000–$750,000; a partial second story over part of the house runs $250,000–$420,000.
Reviewed by Daniel R. Whitcomb, PE · WA PE 48217
Why does a second story start in the crawlspace?
The new floor, its walls and the new roof all bear on the existing house. That weight goes down through first-floor walls that were sized for a roof only, into footings that were poured for a one-story load. Many Eastside ramblers from the 1950s through the 1970s have footings 12 to 16 inches wide and walls framed with 2x4 studs, which may or may not carry a second floor without help.
So the first thing ECD does is look down, not up. The engineer measures the existing footings, checks their condition and depth, and reviews the first-floor framing. The answer sets the budget: if the footings work, the project is a framing project; if they need widening or new interior footings, foundation work is added before anything goes up. You learn which before you pay for design.
What does a second-story project include?
- Foundation investigation and structural feasibility report.
- Design of the new floor plan, stair location, exterior and roof, with the first-floor changes the stair requires.
- Engineering for footing upgrades, new floor framing, shear walls, hold-downs and roof.
- Zoning check for building height, setbacks and floor area limits.
- Permits, temporary weather protection, roof removal and the full build of the new level.
- Extensions of electrical, plumbing and HVAC to the new floor, and a new heating and cooling system sized for the larger house when needed.
Usually excluded
Remodeling first-floor rooms that are not affected by the stair or structure, temporary housing costs and moving and storage of belongings. We tell you at feasibility which first-floor rooms will be disturbed.
How long does a second-story addition take?
- Feasibility and foundation check2–4 weeks
Footings exposed at test locations, framing reviewed, zoning confirmed.
- Design4–8 weeks
Layout, stair, exterior massing and roof, with budget at each option.
- Construction documents4–6 weeks
Full architectural, structural and energy set.
- Permit review8–16 weeks
Zoning, structural and energy review, often with one correction round.
- Foundation upgrades and roof off4–8 weeks
Footings are reinforced first; the roof comes off only when framing is ready to follow.
- Framing, dry-in and completion20–32 weeks
New floor and roof are framed and sealed, then systems and finishes.
How much does a second-story addition cost?
| Scope | Typical cost | Build time |
|---|---|---|
| Raised roof for a loft or bonus room | $120,000–$250,000 | 14–20 weeks |
| Second story over a garage | $180,000–$320,000 | 18–26 weeks |
| Partial second story, 400–600 sq ft | $250,000–$420,000 | 22–30 weeks |
| Full second story, 1,000–1,600 sq ft | $420,000–$750,000 | 28–40 weeks |
What will the city check before approving a second story?
Zoning review measures the new building height against the zone's limit, usually measured from average existing grade to the highest point of the roof, and checks setbacks for the new upper walls. Some Eastside cities also cap total floor area relative to lot size, which matters on smaller lots in Mercer Island, Kirkland and parts of Bellevue. Building review covers the structural load path down to the footings and the lateral system for the taller house; energy review covers the new envelope under the Washington State Energy Code. Our Permit Estimator gives fee and review time ranges by city.
A second story we built
PROJECT · KIRKLAND · ROSE HILLFull second story on a rambler, with new footings under the old wallsThree bedrooms and two bathrooms added above a one-story house; existing footings widened along both bearing lines.Second-story questions
Second-story addition FAQ
For the full feasibility checklist, read Second-story addition feasibility.
How much does it cost to add a second story to a rambler?
A full second story of 1,000 to 1,600 square feet on an Eastside rambler typically costs $420,000 to $750,000 with design, engineering, permits and mid-range finishes. Partial second stories run $250,000 to $420,000. The biggest variable is the foundation: if the existing footings need widening along every bearing line, that work is added before framing begins.
Do we have to move out during a second-story addition?
In most cases, yes, for four to six months. The roof is removed, the first-floor ceiling is opened for new framing and the stair cuts through a room below. Some families stay through foundation work and move out for the framing and dry-in phase. We tell you the move-out window at contract so you can arrange housing.
Can my existing foundation support a second floor?
Sometimes as it is, often with upgrades. The engineer exposes the footings at several points, measures width and depth and checks for cracking and settlement. Narrow footings can be widened in place or supplemented with new interior footings. Severely deteriorated foundations occasionally make a second story uneconomical, which is why we check before design.
How long is the house open to the weather?
Usually two to four weeks. We remove the roof only when wall and floor framing are ready to follow, and cover the opening with engineered temporary protection that is inspected daily. Roof sheathing and underlayment go on as soon as the new rafters or trusses are set. Interior finishes are protected throughout.
Where does the staircase go?
The stair takes about 40 to 50 square feet on each floor and needs to land where it does not cut a main room in half. Common locations are a former hall closet, part of a bedroom or a new entry. We draw two or three stair options at the start because the stair drives the layout of both floors.
Free estimate · Bellevue office
Talk to the engineer before you commit to a plan
A site visit, a scope conversation and a written budget range, at no cost.