COLUMBIA CITY · DADU
DETACHED ADU Builder in Columbia City, Seattle
A detached accessory dwelling unit (DADU) is a fully independent residence on your existing single-family lot. We design and build DADUs that meet rental code, hold long-term value, and look like they belong — not like a kit dropped in the yard. Every project starts with a feasibility study and ends with a turn-key handover.
Build timeline
6–8 months
Typical sqft
400–1,000 sqft
Seattle cost
$140K – $400K
Typical lot
5,500 sf
What detached adu looks like on a Columbia City lot
Columbia City lots commonly fall under NR2, NR3, LR1, LR2. Dominant architectural style: Craftsman / bungalow. Very high — Light Rail-driven
- ✓Stamped architectural set
- ✓Structural + MEP engineering
- ✓Permit submittal & city liaison
- ✓Foundation, framing, weather envelope
- ✓Finish carpentry, cabinetry, fixtures
- ✓Final inspection + warranty package
Other services in Columbia City
Every Golden State service, localized to Columbia City
DETACHED ADU in nearby neighborhoods
DETACHED ADU across Seattle
Columbia City DADU feasibility — $1,500
Lot analysis, Seattle zoning verification, and a fixed price for your Columbia City project.
Book Columbia City feasibilityFrequently asked
Can I build an ADU in Columbia City, Seattle?
Yes — every residential-zoned lot in Columbia City qualifies for at least one ADU under RCW 36.70A.681 and Seattle's implementing code. Variables in Columbia City specifically: (1) lot size and shape — Columbia City has a mix of original platted lots and post-1960 subdivisions, which changes setback geometry; (2) tree retention — mature Columbia City trees over a measured DBH may require an exceptional-tree review; (3) historic overlay — pockets of Columbia City are in a conservation overlay that adds design review. We pre-check all three at feasibility.
What does an ADU cost in Columbia City?
Columbia City ADU all-in cost tracks Seattle citywide medians: $300–$400/sqft for a turn-key 1-bedroom DADU. Columbia City-specific variables include alley access (lowers crane and material handling cost ~$4–9K), older sewer mains (occasionally require side-sewer repair adding $6–18K), and tree-protection fencing. We have built in Columbia City every year since 2017 and our bid accuracy on Columbia City lots is within ±8% of contract on 90% of jobs.
Go deeper: Read the Five hidden ADU costs that wreck Puget Sound budgets guide
What rent will a Columbia City ADU generate?
2026 Columbia City 1-bedroom DADU rents land in the band typical for the surrounding Seattle submarket, generally $2,050–$3,150/mo long-term with a 5–10% premium for true detached privacy over attached units. Mid-term furnished rates run 15–25% higher when within walking distance of transit or a hospital corridor. Our Columbia City rental comps update quarterly from on-market and recently-leased pulls.
How long does a Columbia City ADU project take end-to-end?
Signed feasibility to keys in hand for Columbia City projects: 9–14 months — 6–8 weeks design, 10–16 weeks Seattle permit, 18–26 weeks construction. Columbia City lots with alley access tend to finish at the fast end because staging and crane setup are simpler. Lots requiring driveway construction or grading run the long end. Gantt at contract, weekly updates throughout.
Go deeper: Read the ADU utility upgrades: sewer, water, and electrical service guide
What's special about building in Columbia City vs other Seattle neighborhoods?
Three Columbia City-specific factors: (1) the typical lot age — pre-1950 Columbia City lots often have undersized water services (3/4") that require upsize; (2) the tree canopy — Columbia City's mature canopy means exceptional-tree review is more likely than in post-1990 Seattle neighborhoods; (3) the soil — Columbia City's position on the Puget Lowland glacial till usually supports slab-on-grade. Our Columbia City field experience streamlines all three.
Go deeper: Read the Seattle electrical panel upgrade for ADUs: 100A to 400A (2026) guide
Are there any HOA restrictions in Columbia City?
Columbia City is partly HOA-governed and partly fee-simple. Where HOAs apply, RCW 64.38.034 (effective 2024) blocks outright ADU bans, but ARBs can impose design covenants (siding material, roof pitch, façade articulation). We submit design concepts to ARBs in parallel with permit submittal, adding 4–8 weeks. Most Columbia City HOAs approve when the DADU echoes the primary house's siding and roof material.
What permits and reviews trigger for Columbia City ADUs?
Standard Seattle ADU permit + side-sewer + addressing + water capacity. Columbia City-specific: tree-protection plan if any tree ≥24" DBH is within the construction zone; critical-areas screening if Columbia City portion borders a mapped stream, wetland, or steep slope; drainage review if new impervious exceeds threshold (more likely on small Columbia City lots). We pre-screen all three before submittal.
Go deeper: Read the King County side sewer permits for ADUs: cost & timeline (2026) guide
Can I do a basement ADU in a Columbia City house?
Often yes — Columbia City's housing stock includes many pre-1970 homes with full basements ranging 6'-2" to 8'-0" ceiling height. Basements ≥7'-0" with achievable egress windows convert cleanly at $145–$220K. Lower ceilings (<7'-0") require underpinning to lower the slab — adds $35–$65K plus permit complexity. We measure ceiling and check IRC R310 egress feasibility during initial site visit.
Does Columbia City's zoning allow two ADUs?
Depends on the underlying zone — Seattle's middle-housing implementation under HB 1110/1337 allows two ADUs on most residential lots in Columbia City (DADU + AADU, two AADUs, or stacked DADU). The combined cap is typically 2,000 sqft. Some Columbia City subareas with critical-area overlays restrict to one ADU. We confirm zone designation and count at feasibility against your specific address.
INTERNAL_LINKS / Deep Map