Home addition permit requirements across 16 Seattle-area cities
Side-by-side: which of Seattle, Bellevue, Kirkland, Redmond, Sammamish, Issaquah, Renton, Kent, Federal Way, Mercer Island, Shoreline, Tacoma, Lakewood, Puyallup, Everett, Lynnwood require a permit for a home addition, and what triggers one — each row quoted from the city's own code or permit page, with the source linked. Fees and review times appear where the city publishes them.
15 of 16 cities have authoritative rules on file · 16 always require a permit · 0 depend on the scope · 0 do not.
King County
| Jurisdiction | Permit? | Threshold | Fee | Review days | Source |
|---|---|---|---|---|---|
city | Always | An addition enlarges the building and needs a permit. The Single-Family Addition (BR) permit covers adding LESS THAN 3,000 square feet, or a deck, to an existing single-family residence. At 3,000 square feet or more Bellevue routes the work to its New House Construction or Large Addition permit instead. The BR permit also covers an attached garage or carport, detached buildings such as garages and sheds, retaining walls over four feet, a deck or deck with spa and replacement of existing deck structural framing, a dock, boat house, boat lift or bulkhead over four feet, and a swimming pool, bathing pool or hot tub 24 inches or more deep and in-ground. One BR permit carries the clearing and grading, any required demolition, electrical (except temporary power), mechanical (except fire protection) and plumbing with it — those are not separate applications. | Plan-review fee scales with valuation per UBC Table 1-A. State surcharge $6.50 per building permit. Trade permits (E/P/M) separate. Apply via https://mybuildingpermit.com. | 30–90 days | Cite verified 2026-05-17 |
city | Always | Adding floor area always needs a building permit. Any increase to building footprint or conditioned floor area requires a building permit. A Certificate of Water Availability with fire-flow calculations is required for additions or any change to the building footprint. | Plan-review fee scales with valuation per UBC Table 1-A. State surcharge $6.50 per building permit. Trade permits (E/P/M) separate. | — | Cite verified 2026-05-29 |
city | Always | An addition enlarges the building and needs a permit. A permit is required for all single-family/duplex new construction and additions; no exemption is published. Setback / form / intensity per IMC 18.404. | Plan-review fee scales with valuation per UBC Table 1-A. State surcharge $6.50 per building permit. Trade permits (E/P/M) separate. Apply via https://mybuildingpermit.com. | 45–120 days | Cite verified 2026-05-29 |
city | Always | Adding floor area always needs a building permit. A residential building permit is required for most construction, alteration, or repair work — including changing a building's occupancy, structure, or living space. Intake fees are billed when the submittal is deemed complete (pay within 15 days); issuance fees are due before the permit is issued. | Plan-review fee scales with valuation per UBC Table 1-A. State surcharge $6.50 per building permit. Trade permits (E/P/M) separate. Apply via https://mybuildingpermit.com. | — | Cite verified 2026-05-29 |
city | Always | Adding floor area always needs a building permit. A building permit is required to construct, enlarge, alter, repair, or change the use of a building. Whole-house ventilation compliance is required for new construction and additions greater than 500 square feet of heated space. | Plan-review fee scales with valuation per UBC Table 1-A. State surcharge $6.50 per building permit. Trade permits (E/P/M) separate. Apply via https://mybuildingpermit.com. | — | Cite verified 2026-10-18 |
city | Always | An addition enlarges the building and needs a building permit. Mercer Island distinguishes additions <500sqft (no Intake Screening required) from additions ≥500sqft (Substantial Residential Project, may require Intake Screening prior to review). | Plan-review fee scales with valuation per UBC Table 1-A. State surcharge $6.50 per building permit. Trade permits (E/P/M) separate. | — | Cite verified 2026-04-29 |
city | Always | Adding floor area always needs a building permit. Additions, alterations, and remodels require a building permit with a site plan. Garage conversion to living space also requires a permit. All trade (electrical/plumbing/mechanical) and fire sub-permits must be completed and passed before the Building Final. | Plan-review fee scales with valuation per UBC Table 1-A. State surcharge $6.50 per building permit. Trade permits (E/P/M) separate. Apply through the Redmond ePermitting Service, REPS (https://cityofredmondwa-energovweb.tylerhost.net/apps/selfservice); plan-reviewed permits go through Plan Review Online, and the How to Apply page (https://www.redmond.gov/462/How-to-Apply) says which. | — | Cite verified 2026-05-29 |
city | Always | An addition enlarges the building and needs a permit. Additions always require a building permit — they are expressly excluded from "ordinary repairs" (RMC 4-5-060 §105.2.2). Work started without a permit is subject to a special investigation fee equal to twice the permit fee. | Plan-review fee scales with valuation per UBC Table 1-A. State surcharge $6.50 per building permit. Trade permits (E/P/M) separate. Apply via https://permitting.rentonwa.gov. | — | Cite verified 2026-05-29 |
city | Always | An addition enlarges the building and needs a permit. Single-family/duplex additions require a building permit (MBP: Building → Single-Family Residential → Structure Addition). Demolitions, pools, retaining walls, and detached structures require separate permits. A Sewer Availability Certificate is required when the project exceeds 50% of the assessed value or adds plumbing fixtures. | Plan-review fee scales with valuation per UBC Table 1-A. State surcharge $6.50 per building permit. Trade permits (E/P/M) separate. Apply via https://mybuildingpermit.com. | — | Cite verified 2026-05-29 |
city | Always | Adding floor area always needs a building permit. Any additional floor area requires Construction Permit (Addition or Alteration). Plan review required. ECA + lot coverage + setback compliance verified at intake. | — | — | Cite verified 2026-04-26 |
city | Always | Adding floor area always needs a building permit. Garage conversion to ADU: use Residential Additions checklist + ADU Worksheet. SMC 20.40.210 limits ADUs to 1,200 sqft (exception: interior ADU on separate floor sharing a common roof with the primary residence may exceed 1,200 sqft). Two ADUs per lot maximum per SMC 20.40.210(A), subject to max-density in Table 20.50.020(1). Critical-area triggers (steep slopes ≥15%, wetlands, streams) require a Critical Areas Report and preapplication meeting before submittal. | Apply electronically via eTRAKiT (https://www.shorelinewa.gov/government/departments/planning-community-development/permit-center-remote-services/register-for-a-professional-etrakit-account). Plan-review fees scale with valuation per City fee schedule. State Building Code Council surcharge $6.50 per building permit. Mechanical/Plumbing permits accompany the Building Permit and cannot be deferred; Electrical permits go through WA L&I (not the City). | 30–90 days | Cite verified 2026-05-17 |
Pierce County
| Jurisdiction | Permit? | Threshold | Fee | Review days | Source |
|---|---|---|---|---|---|
city | Always | Adding floor area always needs a building permit. 2021 IRC R105.1 requires permits for "construction, enlargement, alteration, repair, movement, removal, conversion, or demolition" of structures. Additions are never exempt under R105.2. Footprint additions trigger zoning compliance (setbacks, lot coverage, height); vertical additions trigger structural review for the existing foundation/wall framing. WSEC R402-R403 applies to new conditioned area. SEPA threshold typically ≥12,000 sqft total floor area (RCW 43.21C). | Plan-review fee scales with valuation per UBC Table 1-A. State surcharge $6.50 per building permit. Trade permits (E/P/M) separate. Apply through Lakewood's Online Permit Center (https://app.oncamino.com/lakewood_wa), linked with the account steps from the city's Apply for a Permit page (https://cityoflakewood.us/permit-center/). | — | Cite verified 2026-04-29 |
city | Always | Adding floor area always needs a building permit. 2021 IRC R105.1 requires permits for "construction, enlargement, alteration, repair, movement, removal, conversion, or demolition" of structures. Additions are never exempt under R105.2. Footprint additions trigger zoning compliance (setbacks, lot coverage, height); vertical additions trigger structural review for the existing foundation/wall framing. WSEC R402-R403 applies to new conditioned area. SEPA threshold typically ≥12,000 sqft total floor area (RCW 43.21C). | Plan-review fee scales with valuation per UBC Table 1-A. State surcharge $6.50 per building permit. Trade permits (E/P/M) separate. Apply through Puyallup's online permit system, CityView (https://permits.puyallupwa.gov/Portal); the Permit Services page (https://www.puyallupwa.gov/325/Permit-Services) walks through the steps and fees. | — | Cite verified 2026-04-29 |
city | Always | Adding floor area always needs a building permit. Permit required for any addition to an existing building, OR any new accessory structure ≥200 sqft. Alteration/addition <80% of building valuation = Residential Alteration (BLDRA) permit. ≥80% = Residential New Construction (BLDRN) permit (which subsumes site-development review). | Tacoma prices a single-family or duplex addition as one combination building, mechanical and plumbing permit (PDS Fee Schedule Table 8-4): 2.81% of the ICC Building Valuation Data value of the added floor area, plan review at 45% of that fee, and a site development permit (grading and erosion control) at 65% with its plan review at 45% of the building permit fee. Table 1 adds the Technology Program (5%), Natural Resources Program (5%) and Reserve Fund (2%) on permit and plan review fees and Emergency Preparedness (5%) on permit fees; the state building code fee is $6.50. Electrical permits are separate, issued by Tacoma Power (TMC 12.06A). | 30–90 days | Cite verified 2026-04-29 |
Snohomish County
| Jurisdiction | Permit? | Threshold | Fee | Review days | Source |
|---|---|---|---|---|---|
city | Always | Adding floor area always needs a building permit. 2021 IRC R105.1 requires permits for "construction, enlargement, alteration, repair, movement, removal, conversion, or demolition" of structures. Additions are never exempt under R105.2. Footprint additions trigger zoning compliance (setbacks, lot coverage, height); vertical additions trigger structural review for the existing foundation/wall framing. WSEC R402-R403 applies to new conditioned area. SEPA threshold typically ≥12,000 sqft total floor area (RCW 43.21C). | Plan-review fee scales with valuation per UBC Table 1-A. State surcharge $6.50 per building permit. Trade permits (E/P/M) separate. | 30–90 days | Cite verified 2026-10-02 |
city | Always | Adding floor area always needs a building permit. 2021 IRC R105.1 requires permits for "construction, enlargement, alteration, repair, movement, removal, conversion, or demolition" of structures. Additions are never exempt under R105.2. Footprint additions trigger zoning compliance (setbacks, lot coverage, height); vertical additions trigger structural review for the existing foundation/wall framing. WSEC R402-R403 applies to new conditioned area. SEPA threshold typically ≥12,000 sqft total floor area (RCW 43.21C). | Plan-review fee scales with valuation per UBC Table 1-A. State surcharge $6.50 per building permit. Trade permits (E/P/M) separate. | — | Cite verified 2026-04-29 |
How this table is built
Each row reflects the most-recently-verified authoritative rule on file for that jurisdiction and project type. “Pending verification” means we have the jurisdiction in our database but haven't yet personally checked the city page for home addition rules — those rows fall back to county or WA-state baselines until verified. Sources link directly to the city or county page we read on the verified-on date. See our data-quality leaderboard for how we keep these current.