NORTHGATE · AADU
ATTACHED ADU Builder in Northgate, Seattle
An attached ADU shares a wall (and often a foundation) with your primary home. We specialize in carving these units out of basements, daylight floors, and underused side wings — all while preserving the existing home's character and avoiding common moisture, sound-isolation, and egress mistakes.
Build timeline
4–5 months
Typical sqft
300–800 sqft
Seattle cost
$95K – $320K
Typical lot
6,500 sf
What attached adu looks like on a Northgate lot
Northgate lots commonly fall under NR2, NR3, LR1, LR2. Dominant architectural style: Postwar / mid-century. High — Light Rail driven
- ✓Existing-conditions survey
- ✓Egress + life-safety design
- ✓Acoustic + thermal envelope upgrades
- ✓Independent entry construction
- ✓Sub-metering of power & water
- ✓Final inspection + handover
Other services in Northgate
Every Golden State service, localized to Northgate
ATTACHED ADU in nearby neighborhoods
ATTACHED ADU across Seattle
Northgate AADU feasibility — $1,500
Lot analysis, Seattle zoning verification, and a fixed price for your Northgate project.
Book Northgate feasibilityFrequently asked
Can I build an ADU in Northgate, Seattle?
Yes — every residential-zoned lot in Northgate qualifies for at least one ADU under RCW 36.70A.681 and Seattle's implementing code. Variables in Northgate specifically: (1) lot size and shape — Northgate has a mix of original platted lots and post-1960 subdivisions, which changes setback geometry; (2) tree retention — mature Northgate trees over a measured DBH may require an exceptional-tree review; (3) historic overlay — pockets of Northgate are in a conservation overlay that adds design review. We pre-check all three at feasibility.
What does an ADU cost in Northgate?
Northgate ADU all-in cost tracks Seattle citywide medians: $300–$400/sqft for a turn-key 1-bedroom DADU. Northgate-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 Northgate every year since 2017 and our bid accuracy on Northgate 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 Northgate ADU generate?
2026 Northgate 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 Northgate rental comps update quarterly from on-market and recently-leased pulls.
How long does a Northgate ADU project take end-to-end?
Signed feasibility to keys in hand for Northgate projects: 9–14 months — 6–8 weeks design, 10–16 weeks Seattle permit, 18–26 weeks construction. Northgate 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 Northgate vs other Seattle neighborhoods?
Three Northgate-specific factors: (1) the typical lot age — pre-1950 Northgate lots often have undersized water services (3/4") that require upsize; (2) the tree canopy — Northgate's mature canopy means exceptional-tree review is more likely than in post-1990 Seattle neighborhoods; (3) the soil — Northgate's position on the Puget Lowland glacial till usually supports slab-on-grade. Our Northgate field experience streamlines all three.
Go deeper: Read the Cold-weather concrete pours in the Puget Sound (2026 field guide) guide
Are there any HOA restrictions in Northgate?
Northgate 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 Northgate HOAs approve when the DADU echoes the primary house's siding and roof material.
What permits and reviews trigger for Northgate ADUs?
Standard Seattle ADU permit + side-sewer + addressing + water capacity. Northgate-specific: tree-protection plan if any tree ≥24" DBH is within the construction zone; critical-areas screening if Northgate portion borders a mapped stream, wetland, or steep slope; drainage review if new impervious exceeds threshold (more likely on small Northgate 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 Northgate house?
Often yes — Northgate'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 Northgate'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 Northgate (DADU + AADU, two AADUs, or stacked DADU). The combined cap is typically 2,000 sqft. Some Northgate subareas with critical-area overlays restrict to one ADU. We confirm zone designation and count at feasibility against your specific address.
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