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Basement Finish Cost in Seattle, Washington
The median declared cost of a basement finish in Seattle, Washington is $50,000, based on 31 residential building permits issued in the last 24 months.
Updated November 2026 · next refresh December 2026 · computed from permits issued through November 2026.
| Median declared cost | $50,000 |
|---|---|
| Typical range (middle half) | $17,500 – $97,500 |
| Full spread (10th–90th percentile) | $4,000 – $150,000 |
| Permits in sample | 31 |
| Period covered | 2024-11-12 to 2026-11-12 |
| Source | City of Seattle building permits (open data) |
How to read this number
These are declared permit values — the job value the applicant reported to the City of Seattle when the permit was filed. Declared values are a real-world sample of what these projects get filed at, but they are not final invoices: applicants have no reason to inflate them, and final costs often run higher once the work is done. Use the median as a planning anchor and the range to see how far real projects spread.
One more caveat: a permit value covers the whole permitted job. When a basement finish is filed together with other work, the single declared figure covers all of it — one reason the top of the range runs high.
Finishing your own basement? The walls come first — the drywall calculator counts sheets, compound and tape for the space — and every quote keys off the floor area, which the square footage calculator gives you from two measurements.
How the costs spread
Half of all permits in the sample declared between $17,500 and $97,500. The full spread is wider: the cheapest 10% declared under $4,000, and the most expensive 10% declared over $150,000.
How to read this: half of all basement finish permits declared less than the median; 90% declared less than the right-hand figure.
How this project gets permitted in Seattle
Seattle permit descriptions name the review path each job actually took. Of the 31 permits in this sample whose descriptions name it, 81% went through subject-to-field-inspection (STFI) (25 STFI vs 6 full plan review). STFI is the city's faster track for work that does not need a full plan check; structural work goes through plan review.
The permit itself is a small line item. SDCI charges by declared value (Development Fee Index, Seattle Municipal Code 22.900D.010, Tables D-1 and D-2): at this project's median declared value of $50,000, the building permit and plan review on the subject-to-field-inspection (STFI) path come to about $1,618, including the 5% technology fee and the $6.50 state building-code fee. Across the middle half of declared values ($17,500–$97,500), the same fees run about $872–$2,633. Trade permits (electrical, plumbing, mechanical) are charged separately.
Recent basement finish permits in Seattle
Anonymized examples from the sample — work description and declared value as filed, no addresses or names.
| Issued | Permit description | Declared cost |
|---|---|---|
| Oct 2026 | Construct alterations to main floor finish basement and add window wells to existing one-family dwelling per plan. | $50,000 |
| Oct 2026 | Construct alterations to include converting unconditioned basement to conditioned living space for one-family dwelling per plan. | $150,000 |
| Oct 2026 | Construct interior alterations to finish basement of one family dwelling subject to field inspection STFI. | $100,000 |
| Sep 2026 | Remodel (e) conditioned basement of one family dwelling per plan subject to field inspection STFI | $85,000 |
| Sep 2026 | Screen for STFIInterior remodel and convert the basement into living space convert the garage into living space. | $100,000 |
| Aug 2026 | Construct alterations to add habitable living space at existing unfinished basement for one-family dwelling subject to field inspection [ST… | $45,000 |
Methodology
We pull every issued residential building permit the City of Seattle publishes through its open-data portal (Socrata), keep permits from the last 24 months with a declared value above zero, and classify each one by the project its description names. Records above $2,000,000 and statistical outliers (outside 1.5× the interquartile range) are excluded before the median is computed. Every classifier rule set is spot-checked by hand against 20 sampled permits before a project type is published. This page is refreshed monthly from the permit archive.
Frequently asked questions
How much does a basement finish cost in Seattle, Washington?
Based on 31 Seattle, Washington building permits issued in the last 24 months that included a basement finish, the median declared cost was $50,000. The middle half of permits declared between $17,500 and $97,500.
Where do these numbers come from?
They are computed from building permits published by the City of Seattle through its open-data portal. Each permit carries a declared job value reported by the applicant. We filter to residential permits, classify them by the project described, drop outliers, and publish the median and the middle-half range.
Why might my quote be higher than the permit median?
The declared value is what the applicant reported to the city when the permit was filed, and final project costs often run higher. Scope also varies widely: a permit value covers the whole permitted job, so a remodel combined with other work declares one combined figure. Treat the median as a planning anchor, not a bid.
What does the declared value on a basement finish permit cover?
Whatever work the permit describes — for combined projects that can include rooms or work beyond the headline project. That is why we publish the range alongside the median: it shows how wide real declared costs spread for this project type in Seattle.
Does a basement finish in Seattle need plan review?
Most take the subject-to-field-inspection (STFI) path: 81% of the 31 permits in our sample whose descriptions name the review path went that way (25 STFI, 6 full plan review). SDCI decides the path at intake — non-structural work usually qualifies for STFI, structural work does not.
How much is the permit fee for a basement finish in Seattle?
SDCI charges by declared value. At this project's median declared value of $50,000, the building permit plus plan review on the subject-to-field-inspection (STFI) path comes to about $1,618, including the 5% technology fee and the $6.50 state fee (Seattle Municipal Code 22.900D.010). Trade permits are extra.
Does finishing a basement in Seattle need a permit?
Work that creates habitable space — bedrooms, living space, a new bathroom — is permitted work in Seattle, and every record in this sample is an issued permit for exactly that. Most (81% of those naming a path) went through subject-to-field-inspection; adding a bedroom usually adds an egress-window requirement, which is why so many of these permits mention one.
Plan the work
Drywall Calculator
Drywall sheets for any room, plus the mud, tape and screws to finish them — at published estimating rates.
CalculatorFlooring Calculator
Boxes of vinyl, laminate or hardwood for your room, with the right waste factor for each material.
CalculatorPaint Calculator
Gallons of paint and primer for any room, minus doors and windows, times your coats — with cost.
More Seattle remodeling costs
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Cost in SeattleBathroom Remodel
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Cost in SeattleDeck Build
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Cost in SeattleHouse Addition
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Cost in SeattleADU / DADU
Median $183,517 across 437 permits.
About the author
Harrison Alley is a web publisher and data enthusiast based in Dallas, Texas. He built Urbarama’s remodeling calculators and maintains them.
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