City of Mercer Island building permits: fees, timelines & requirements (2026)
What needs a permit in City of Mercer Island and what triggers one — each row quoted from the city's own code or permit page, with the source linked and the source page checked daily for changes. Fees and review times appear where the city publishes them. Covers ADU, addition, kitchen, bathroom, basement, deck, fence, siding, windows, flooring, roofing, HVAC, electrical, plumbing, and ancillary permits (King County).
21 of 24 project types have authoritative rules on file · 12 always require a permit · 10 depend on the scope · 0 do not.
Get your lot in 3D with zoning, setbacks, and the exact permits your project needs — cited to City of Mercer Island's source.
Permit department
Apply via MyBuildingPermit.com.
Adopted code cycles
2021 IRC w/ WA amendments · 2021 WSEC
Resources
Construction permits
| Project | Permit? | Threshold | Fee | Review days | Source |
|---|---|---|---|---|---|
| Kitchen remodel | Depends on scope | No permit for cabinets, counters, paint or tile. A permit once you move plumbing, add circuits, run gas or change walls. Cosmetic-only refresh (cabinets, countertops, flooring, paint) without structural/electrical/plumbing changes is generally exempt under 2021 IRC R105.2 (work exempt from permit). Any new circuit, fixture relocation, or structural change requires permits. | Fees set by jurisdiction. WA Building Code Council surcharge: $6.50 per building permit. Trade permits separate. | Not published by the city | Cite verified 2026-04-29 |
| Bathroom remodel | Depends on scope | No permit for tile, paint or a same-spot fixture swap. A permit once plumbing moves, circuits are added or the tub or shower goes. Like-for-like fixture replacement in same location with no plumbing rerouting and no new circuits: typically exempt under 2021 IRC R105.2(2)(g). Any relocation, new fixture, new circuit, or shower-pan replacement triggers permits. | Fees set by jurisdiction. Plus separate electrical, plumbing, and mechanical permits. | Not published by the city | Cite verified 2026-04-29 |
| Basement finish | Always | Finishing a basement into habitable space needs a building permit; egress and ceiling height are the usual review items. 2021 IRC R310: every sleeping room below grade requires emergency escape and rescue opening (egress window). Min sill height 44in, min net clear opening 5.7 sq ft (5.0 grade-floor), min width 20in, height 24in. Ceiling height min 7ft (R305). Entire newly conditioned area must comply with WSEC R402. | Plan-review fee scales with valuation. State surcharge $6.50. | Not published by the city | Cite verified 2026-04-29 |
| Deck | Depends on scope | A deck 30 in or under and not over a basement or story below is exempt outside critical and flood-hazard areas. Decking-board replacement is separately exempt. Permit NOT required for sidewalks, decks and driveways constructed under IRC, not more than 30in above grade and not over any basement or story below. Decking replacement on existing decks WITHOUT changing/adding structural members and WITHOUT removing guardrails is also exempt. Per the multi-jurisdiction tip sheet, the 30-inch measurement is taken vertically to the grade below at any point within 36 inches of the outer edge of the deck. Critical-area / flood-hazard exemption rule applies. | Most jurisdictions handle decks as field-inspection or simplified plan review. | Not published by the city | Cite verified 2026-04-29 |
| Fence | Depends on scope | No permit for a fence 6 ft or under. Fences not over 6 feet (1,829 mm) high are exempt. Maximum fence height per Mercer Island Permit FAQ: 6 feet. | Typically no fee unless permit required. | Not published by the city | Cite verified 2026-04-29 |
| Siding | Depends on scope | Non-structural wood or vinyl siding is exempt; veneer, stucco or EIFS needs a permit. Exempt for non-structural wood and vinyl siding. NOT exempt for veneer, stucco, or exterior finish and insulation systems (EFIS). Exemption does not apply to RCW Chapter 64.55 structures. | Typically minimal fee — like-for-like usually exempt. | Not published by the city | Cite verified 2026-04-29 |
| Window replacement | Depends on scope | In-kind replacement is exempt when no structural member changes. A new or larger opening or a structural alteration needs a permit. Exempt: in-kind window replacement for IRC structures where no alteration of structural members is required, safety glazing is provided where required, and window fall protection is provided where required. Permit required for: new openings, larger openings, or any structural alteration. | Like-for-like usually no permit fee. Structural changes scale with valuation. | Not published by the city | Cite verified 2026-04-29 |
| Flooring | Depends on scope | Floor finishes are exempt; subfloor, joist or radiant work needs a permit. 2021 IRC R105.2(1)(j) exempts floor finishes (carpet, vinyl, hardwood, tile). Permit required if subfloor structure is modified, joists altered, or radiant heat installed. | No permit fee for surface flooring. | Not published by the city | Cite verified 2026-04-29 |
| ADU / DADU | Always | An ADU or DADU always needs a building permit, and usually trade permits with it. MICC 19.02.030 (interim regs implementing WA HB 1337, eff. 6/30/2024): ADU min 220 sqft GFA, max 1,000 sqft GFA AND capped at 25% of the parcel's allowed GFA (whichever is less). Up to 2 ADUs allowed per lot. Owner-occupancy NOT required (preempted by HB 1337). Setbacks: per underlying R-zone (front 20', side 5', rear 25' in R-9.6, etc.; see MICC 19.02.020(B)). Detached ADU may sit at a lot line if the lot line abuts a public alley. Parking: 1 stall/unit for lots <6,000 sf, 2 stalls/unit for lots ≥6,000 sf. Parking waived if parcel is within 1/2 mile WALKING DISTANCE of a light rail station (not generic "major transit"). Separate addressing assigned by City after Land Use approval. HB 1337 caps impact fees at 50% of SFR impact fees. | Phase A Land Use fee per MI Fee Schedule (Type II Land Use Review line). Phase B Building permit fee is valuation-based: ~$2,100 building + ~$1,365 plan review (65%) + WA BCC $6.50 + per-fixture plumbing/mech fees at $280k valuation. Impact fees (school, transportation, parks) ~$5,000-$15,000 BEFORE HB 1337's 50% ADU cap — confirm MI has updated its schedule. | 30–90 days | Cite verified 2026-05-16 |
| Roofing | Depends on scope | In-kind re-roofing is exempt unless sheathing is replaced or the material type changes. Permit required when: sheathing is replaced OR the type of roofing material is changed. Exempt: in-kind re-roofing of one- and two-family dwellings provided the roof sheathing is not removed or replaced. | Flat fee or valuation-based, per the city's fee schedule. | Not published by the city | Cite verified 2026-04-29 |
| HVAC | Always | Any equipment install, replacement or relocation needs a mechanical permit. WAC 51-52 (2021 IMC) and WAC 51-56 (2021 UPC) require mechanical permit for any equipment install, replacement, or relocation. WSEC R403 requires sizing per Manual J/S/D for new equipment. | Mechanical permit + electrical permit (if new circuit) + plumbing permit (if condensate to drain). | Not published by the city | Cite verified 2026-04-29 |
| Electrical | Depends on scope | Essentially all electrical work needs a permit; only like-in-kind replacement on the L&I minor list is exempt, and even that needs an inspection request. WAC 296-46B (WA-adopted 2020 NEC) requires an electrical permit for essentially all electrical work. L&I issues them in most jurisdictions; some cities run their own program. L&I publishes the exemption list, and it is narrower and more specific than "ordinary repairs": travel trailers; plug-in household appliances; and the LIKE-IN-KIND replacement of lamps, a single set of fuses, a single battery under 150 amp-hour, control components such as contactors, relays, timers, starters and circuit boards, one household appliance, circuit breakers (branch-circuit overcurrent protection only, per NEC 100), single-family residential luminaires, up to five snap switches, dimmers, receptacle outlets, thermostats, heating elements or identical luminaire ballasts, sign and outline-lighting components replaced on-site by an electrical contractor without modifying the system, and one motor of ten horsepower or smaller. AN EXEMPTION FROM THE PERMIT IS NOT AN EXEMPTION FROM INSPECTION: L&I requires an inspection request before any electrical work is covered, no later than 3 business days after the work is finished or 1 business day after any part is energized, whichever comes first, and failure to request one can carry civil penalties. | Electrical permit fees are set by circuit count and service size in the issuing agency's fee schedule. | Not published by the city | Cite verified 2026-04-29 |
| Plumbing | Depends on scope | Installing, replacing or relocating a fixture, water heater or piping needs a permit; a like-for-like faucet swap is exempt. WAC 51-56 (2021 UPC) requires plumbing permit for installation, replacement, or relocation of any plumbing fixture, water heater, or piping. Like-for-like faucet replacement is exempt. | Plumbing permit fees are set by fixture count in the city's fee schedule. | Not published by the city | Cite verified 2026-04-29 |
| Addition | Always | Adding floor area always 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. | Not published by the city | Cite verified 2026-04-29 |
Ancillary & non-building permits
| Project | Permit? | Threshold | Fee | Review days | Source |
|---|---|---|---|---|---|
| Demolition | Always | Demolishing a structure or a substantial part of one needs a permit; asbestos and lead notifications are separate. 2021 IBC Section 105.1 + WA-adopted IRC R105.1: demolition of any structure or portion thereof requires a permit. Tear-out of interior finishes only is generally treated as alteration. Asbestos / lead notification often required separately under WAC 173-303 / 296-62. | Demolition fees commonly charged as flat fee or by structure size. State surcharge $6.50 applies. | Not published by the city | Cite verified 2026-05-02 |
| Right-of-way | Always | Any work in or occupation of the public right of way needs a right-of-way permit from public works. Issued by city public works (or SDOT in Seattle) under local ROW ordinance. Triggered by physical occupation of or work within the public ROW including driveway aprons, curb cuts, sidewalk replacement, utility tie-ins, hauling routes, and temporary construction staging. | Right-of-way permit fees vary by city: a base fee for a residential driveway or curb cut, plus a per-day occupancy charge if the street is obstructed. | Not published by the city | Cite verified 2026-09-24 |
| Side sewer | Always | A new side-sewer connection, a repair beyond about 2 ft, relining or capping needs a permit from whichever utility owns the main. The side-sewer permit is issued by whichever utility owns the sanitary sewer — the city, a sewer or water district, or a regional utility — under that utility's own code, with WAC 51-56 (2021 UPC) governing how the building sewer is laid. WHICH UTILITY IS A PER-PROPERTY FACT: a lot can sit inside a city for permitting and outside its sewer district, so confirm the owner of the main before applying. Triggered by a new connection, repair of more than about 2 ft of pipe, relining (CIPP), or capping at the property line for a demolition. | Side-sewer permit fees are set by the utility that owns the main; some add a depth-based surcharge. Utility-issued, not building-permit-issued. | Not published by the city | Cite verified 2026-09-06 |
| Stormwater / drainage | Always | New or replaced impervious surface and land disturbance are reviewed under the drainage manual this jurisdiction adopts; the threshold is the manual's. Ecology's Stormwater Management Manual for Western Washington (SWMMWW, 2024 edition) is the state floor. A municipal stormwater permittee may instead adopt a REGIONAL manual Ecology has determined equivalent, and most do — some counties publish their own, some cities publish their own, and others adopt Ecology's directly. WHICH MANUAL APPLIES IS A PER-JURISDICTION FACT and it changes the numbers: review thresholds for new plus replaced impervious surface and for land-disturbing activity differ between manuals, so read this jurisdiction's own adopting chapter before quoting one. Critical-area and closed-basin parcels get stricter review under every manual. | Drainage review fees are commonly tiered by project size in the city's fee schedule. | Not published by the city | Cite verified 2026-05-02 |
| Land-use / zoning | Always | A variance, conditional use, plat or design review is a land-use decision that precedes the building permit. Triggered when a project does not conform to the strict letter of the zoning code. Variances require a hardship finding under most city codes. Design review thresholds vary (Seattle: most multifamily + non-residential >4,000 sqft; many cities: design review only in designated districts). | Land-use fees vary widely; a variance usually carries an application fee plus cost recovery for the hearing examiner. | Not published by the city | Cite verified 2026-09-24 |
| Tree removal | Not verified | This city protects trees under its own ordinance and Kolmo has not verified the size threshold. Ask the city before cutting; some cities prohibit removal above a size rather than permit it. Triggered by removal of a tree that the city's own tree ordinance protects — commonly defined by a diameter at breast or standard height, a listed-species table, a grove or heritage designation, or a canopy-cover target. This baseline row carries NO verified local threshold; read the city's tree chapter before quoting a number. Some cities do not permit removal above a size at all — they prohibit removal of regulated trees outside enumerated exceptions, so a "permit required at X inches" reading is wrong there. | Tree-removal permit fees are set per permit or per tree in the city's fee schedule; some cities require replacement bonds. | Not published by the city | Cite verified 2026-09-06 |
| Signs | Always | Permanent signs need a sign permit; small temporary residential signs are usually exempt. City sign code (typically Title 22 or 23) governs. Wall, freestanding, projecting, awning, and electronic message signs all require permits. Most cities exempt small temporary residential signs (real-estate, political) under area thresholds (~6 sqft). | Sign permit fees are set in the city's fee schedule, plus an electrical sub-permit for an illuminated sign. | Not published by the city | Cite verified 2026-09-24 |
Building in City of Mercer Island?
Kolmo Construction is a licensed Washington general contractor — KOLMOL*753JS, bonded and insured — working throughout City of Mercer Island and King County. We pull the permits listed above and build the project.
How this page is built
Each row is the most-recently-verified authoritative rule on file for City of Mercer Island and the listed project type. “Pending verification” means we have City of Mercer Island in our database but haven't yet personally checked the city page for that project — those rows fall back to King-County or Washington-state baselines until verified.
See the data-quality leaderboard for how we keep these current, or run an address-specific lookup on the main permits page.