Attached ADU (AADU) Permits in Lynnwood
An ADU built inside or attached to the primary residence — basement conversion, garage conversion, or bump-out addition. Lower cost; constrained by the primary footprint.
Free lookup: your lot’s zoning and setbacks, with an attached ADU placed on it to move and turn.
Permit fees in Lynnwood
Set by the Lynnwood fee schedule.
Lynnwood fee scheduleLynnwood prices an ADU's building permit on the value of the work, by the ICC valuation table or the square footage, whichever is greater: $1,181.86 for the first $50,000 plus $12.62 for each $1,000 more up to $100,000, and $1,812.71 for the first $100,000 plus $10.32 for each $1,000 more up to $500,000. Plan review is 65% of that fee. For new construction, the plumbing and mechanical permits are each 10% of the building permit fee; in an addition they are $257 for up to 4 fixtures or pieces of equipment and $22 for each one more. The City issues the electrical permit, priced for new construction on its electrical valuation table, $114 up to $1,000. A 2.5% technology fee is added (LMC 3.104).
Review timeline
Not published by Lynnwood.
What Lynnwood asks for with an attached ADU
Every application (12)
- ADU permit (land use application), approved and recorded before the building permit
- Residential building permit application (combo permit: building, mechanical, plumbing), after the ADU permit
- Project narrative, with the owner-occupancy statement
- Owner-occupancy affidavit and the ADU permit, recorded with the Snohomish County Auditor
- Site address
- Snohomish County parcel number
- Site plan, in the plan set
- ADU entrance, its added parking, and the no-separate-sale statement, on the site plan
The other 4
- 13-Element Checklist, or a SWPPP at 2,000 sq ft or more of land disturbance
- Floor plan
- Energy code and whole house ventilation information, on the plans
- Energy code supporting calculations and worksheets
Where the lot or the work calls for it
Where the ADU adds onto the house or changes its structure
- Foundation plan
- Roof + floor framing plan
- Structural design notes (loads, materials, inspections)
Where the ADU adds onto the house or changes its outside walls, windows or roof
- Typical building / wall section
- Building elevations N/S/E/W
- Major materials schedule
Where the work changes the outside walls, windows or roof
- Glazing + door schedule (NFRC U-factor / SHGC)
Where the lot is in a landslide hazard area or is in a seismic hazard area
- Geotechnical report
From the city’s own documents: City of Lynnwood Development & Business Services — Accessory Dwelling Unit (ADU) Submittal Checklist (June 2022) · City of Lynnwood Development & Business Services — Residential Permit Checklist (New Construction & Additions) (June 2024) · Lynnwood Municipal Code 21.42.110(G), Accessory Dwelling Units, last read October 22, 2026. An address’s own page checks its lot for slopes, flood zones and critical areas.
AADU-specific requirements
- Egress on every bedroom — IRC R310 net clear opening ≥5.7 sf; sill ≤44″ from floor.
- Smoke + CO alarms — interconnected throughout primary + AADU per IRC R314/R315.
- 1-hr separation — required between AADU and primary in some cases; otherwise a continuous draft stop.
- Independent kitchen + bath — full plumbing + cooking provision in the AADU.
- Address or unit number — the city or county assigns addresses; ask the permit center whether the unit gets its own.