What Did Your Seattle Construction Project Actually Cost?
Almost every builder has a cost-per-square-foot number in their head. Very few can say which projects it came from, what was included in it, or when it was last true.
This page explains how residential construction costs behave in Seattle and how to build a cost picture you can rely on when you underwrite the next site.
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Why cost per square foot varies
Cost per SF is a ratio, and both halves of it move. The numerator changes with scope, site conditions, finish level and when the work was bought. The denominator changes with how you measure square footage — whether garages, decks, basements and unfinished space are in or out. Two builders quoting the same project can be two hundred dollars apart on paper and identical in reality.
- Scope and finish level
The same footprint at two finish levels is not the same project. Compare within finish tiers, not across them.
- Square footage definition
Decide once whether garages, basements, decks and unfinished space count, and apply it to every project.
- Site conditions
Slope, soils, access, shoring, retaining and utility runs. On small infill lots these can move the whole number.
- Construction period
Pricing from three years ago is history, not a benchmark. Note when the work was bought.
- Unit count
Repetition on a multi-unit townhome site changes the per-SF result relative to a one-off house.
Hard costs versus total project costs
Hard costs
Site work, structure, envelope, systems, finishes and the general conditions to build it. This is the number to use when comparing construction execution across projects.
Soft costs
Design, permits, fees, consultants, insurance, marketing and closing costs. Often the quietest source of variance between projects.
Financing and carry
Interest and fees during construction and through the sales period. Directly tied to duration, which makes schedule a cost line.
Land basis
Kept separate from cost per SF. Blending land into a construction metric hides which half of the deal actually worked.
Total project cost
Land, hard, soft and financing together. This is the number that determines profit — and the number most builders track least consistently.
Consistency
Whichever definitions you choose, applying them identically on every project is what makes comparison possible.
Why one project is not a benchmark
A single completed project gives you one data point produced under one set of conditions. It cannot tell you whether your framing costs are structurally high or whether one subcontractor had a bad month. That answer requires several comparable projects measured the same way.
- Comparing similar projects
Build the comparison set first: same product type, similar size, similar unit count, similar construction period. Then look at the numbers.
- Tracking cost trends over time
Watch categories across projects rather than totals. A total can look stable while two categories move in opposite directions.
- Estimating error versus execution error
Budget-versus-actual by category separates a bad estimate from a bad build. The fixes are different.
- Underwriting future developments
Completed projects give you contingency and cost assumptions grounded in evidence instead of habit.
Seattle-specific project differences
Seattle infill projects rarely look alike. A townhome site in Ballard, a small-lot house in Beacon Hill and an SFR with a DADU in Wallingford carry different site work, different review timelines and different buyers. Neighborhood, product type, size and timing all move the cost result — which is why a citywide average is usually the least useful number available.
Neighborhood
Access, slope, utility age and buyer expectations differ across the city and show up in both cost and price.
Product type
Townhome, SFR, cottage, ADU and DADU projects have distinct cost structures and should be measured separately.
Project size
Fixed costs spread differently across 1,400 SF than across 4,000 SF.
Timing
Permit and review duration, seasonality and the pricing environment during construction.
Weighted cost per square foot
Do not average the per-SF ratios of several projects. Add the comparable costs, add the comparable square footage, then divide. Otherwise a small project carries the same weight as one three times its size.
- Project A
- $1,240,000 hard cost · 4,100 SF
- $302 / SF
- Project B
- $860,000 hard cost · 2,600 SF
- $331 / SF
- Project C
- $1,510,000 hard cost · 5,300 SF
- $285 / SF
- Weighted (total ÷ total)
- $3,610,000 ÷ 12,000 SF
- $301 / SF
- Simple average of ratios
- (302 + 331 + 285) ÷ 3
- $306 / SF
The two methods disagree, and the weighted figure is the one that reflects the dollars you actually spent. Keep land, soft costs and financing separately identifiable rather than folded into a construction figure.
Hypothetical illustration · not a Seattle average
Related Guides
- Seattle Infill Development
How Seattle infill projects actually run.
- Construction Cost Per Square Foot
How to compare cost/SF correctly.
- Seattle Townhome Builders
Townhome economics in Seattle submarkets.
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