Pricing from our last 19 Puget Sound basement permits. Four scope tiers, the code that actually governs ceiling height + egress, waterproofing systems, and 5-year ROI for the tier that pays back — permitted basement AADUs.
Best fit: Owner-occupied recreation space; no new bedrooms or rentable use.
Best fit: Family suite, returning college student, occasional guest stays.
Best fit: Long-term rental owners, multi-gen households, house-hacker buyers.
Best fit: Pre-1950 Seattle/Tacoma homes with sub-6'8" ceilings or active water issues.
| City | $/sf range | Permit fees | Build window | Notes |
|---|---|---|---|---|
| Seattle (SDCI) | $135 – $310/sf | $3,200 – $7,800 | 12 – 18 wk | Most basement AADUs trigger an SDP review; existing-FAR credits favor conversion over new build. |
| Bellevue | $140 – $330/sf | $3,400 – $8,200 | 10 – 14 wk | Stricter egress + emergency-rescue review than Seattle; faster cycle overall. |
| Kirkland / Redmond | $120 – $280/sf | $2,400 – $5,800 | 9 – 13 wk | Online portal; basement AADUs frequently approved when ceiling height already complies. |
| Tacoma | $95 – $230/sf | $1,600 – $4,200 | 8 – 12 wk | Older homes mean more underpinning candidates; favorable rental market for finished basements. |
| Snohomish County | $110 – $260/sf | $2,000 – $4,800 | 9 – 14 wk | PUD coordination on sub-panel feeds; septic-tied homes require capacity letter for AADU. |
7–0" finished in habitable rooms; 6–8" at beams & ducts (IRC R305 / 2024).
Sleeping room: 5.7 sf min opening, 24" h × 20" w min, sill ≤ 44" AFF (IRC R310).
Connect to footing drain or daylight; min 9 sf area, 36" projection (IRC R310.2).
Class-I vapor retarder on warm side; rigid foam interior face counts as continuous insulation (WSEC R702.7).
Passive sub-slab system required in Zone-1 counties (passive depressurization stub).
50 cfm intermittent or 20 cfm continuous, ducted to exterior with backdraft damper.
| Scope | Spend | Monthly rent lift | Recoup @ sale | Notes |
|---|---|---|---|---|
| Basic finish | $38k – $72k | n/a (owner use) | 65 – 80% | ROI mostly comes from added livable sqft on appraisal. |
| Finished suite + 3/4 bath | $78k – $145k | n/a (owner use) | 60 – 75% | Lifestyle and pre-listing value play. |
| Permitted basement AADU | $148k – $235k | $1,650 – $2,650/mo | 70 – 105% | Best ROI category — rentable + adds appraised income stream. |
| Underpin + dig-out | $245k – $480k+ | $1,750 – $2,850/mo | 55 – 75% | Structural rescue plays. ROI compresses but houses become saleable. |
Send us your ceiling height, sump status, and ZIP. We'll come back with the tier your basement actually qualifies for and a fixed-scope range from your jurisdiction's fees.
Send your basement dimensions (or address) and we'll tell you which of the 3 cost drivers apply to your project, and where the number lands.
Address + ceiling height + finished y/n. PDF in 48h.
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