Additions and Remodeling in Puget Sound: Costs, Permits and How to Hire
A ground-floor addition in the Seattle area costs $350 to $550 per square foot, a second-story addition $400 to $650, and a whole-house remodel of an average home $250,000 to $700,000. These are structural projects: they need engineering, a full permit and a contractor who can manage design, trades and inspections over months.
What additions and major remodels cost here
| Project | Installed range | Typical total timeline |
|---|---|---|
| Load-bearing wall removal with beam | $8,000 – $35,000 | 2 – 6 weeks including permit |
| Bump-out, 40 – 120 sq ft | $40,000 – $90,000 | 3 – 5 months |
| Ground-floor addition | $350 – $550 per sq ft | 6 – 10 months |
| Second-story addition | $400 – $650 per sq ft | 10 – 14 months |
| Whole-house remodel | $250,000 – $700,000 | 8 – 14 months |
Ranges include design, engineering, permits and mid-range finishes. Kitchens and bathrooms inside an addition push the per-foot cost toward the top.
Out or up
Building out keeps the house livable during most of the work and is cheaper per square foot, but needs room within setbacks and lot coverage. Building up keeps the yard and suits small lots, but the roof comes off, the foundation and first-floor walls usually need strengthening, and a stair takes space downstairs. The build out or build up guide compares them in detail.
When an engineer is required
Any project that changes how the house carries weight needs a licensed engineer's drawings for the permit: removing or cutting a bearing wall, adding a floor, building an addition, enlarging a large opening, or changing a foundation. The engineer sizes beams, posts and footings, checks the house's resistance to earthquakes, and stamps the plans the city reviews. Bringing the engineer in early, before the design is finished, avoids redesign later.
Seismic and foundation upgrades
Many Seattle-area houses built before 1980 are not bolted to their foundations. An addition or second story is the moment to fix that, because the engineer will look at the foundation anyway and adding weight to an unanchored house makes the risk worse. Foundation bolting and cripple-wall bracing are a small share of an addition budget.
Permits for additions and remodels
Additions, second stories, wall removals and major remodels all need building permits with structural drawings and an energy code worksheet, plus trade permits. Lots near steep slopes, streams, wetlands or shorelines get additional review, and large trees can limit where an addition goes. Review times range from several weeks to several months. The Permit Checker covers the basics for your city.
How to vet a remodeling contractor
- Confirm L&I registration, bond and insurance; for large projects, check the bond amount and claims history.
- Ask who produces the drawings and who the engineer is.
- Ask to visit a current job site, not just see photos.
- Ask how they price unknowns: allowances, contingency, and how change orders are approved.
- Ask for a schedule with milestones and the payment tied to each.
- Ask who handles the permit and inspections.
Addition and remodel quote red flags
- A fixed price without drawings, or drawings without engineering.
- Payments due ahead of milestones rather than after them.
- No contingency or allowance language on a house more than fifty years old.
- A contractor who suggests skipping the permit to save time.
- Vague finish allowances that leave the real cost undefined.
Additions and remodeling guides by city
- Additions & remodeling in Seattle old foundations, narrow lots and SDCI review→
- Additions & remodeling in Bellevue ramblers, view limits and whole-house remodels→
- Additions & remodeling in Kirkland second stories and tree-constrained lots→
- Additions & remodeling in Redmond 1980s homes and HOA review→
Questions about additions and remodels
Do I have to move out?
For a ground-floor addition, usually not until the final connection to the house. For a second story or whole-house remodel, most families move out for at least part of the work.
How much contingency should I keep?
Ten to fifteen percent of construction cost on older houses, less on newer ones.
Will my property taxes go up?
The county reassesses after the work is permitted and complete, based on added value.
Can I add a second story to any house?
Not every house. The foundation, walls and local height limit decide. An engineer's feasibility visit answers it before you pay for design.
Is it cheaper to tear down and rebuild?
Sometimes, when the house is small, in poor condition and on a valuable lot. Ask for both numbers when the comparison is close.