City of Mercer Island building permits: fees, timelines & requirements (2026)
What needs a permit in the 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 weekly 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).
19 of 23 project types have authoritative rules on file · 11 always require a permit · 12 depend on the scope · 0 do not.
Get your lot in 3D with zoning, setbacks, and the exact permits your project needs — cited to the City of Mercer Island's source.
Permit department
Mercer Island Community Planning & Development
Adopted code cycles
2021 IRC w/ WA amendments · 2021 WSEC
Resources
Construction permits
| Project | Threshold | Fee | Review days | Source |
|---|---|---|---|---|
| Kitchen remodel Depends on scope | Finish work (cabinets, counters, tile, paint) needs no permit unless it alters an existing required accessible feature or the building is a multiunit residential building under RCW 64.55. Moving plumbing, replacing a faucet or other valve, new circuits, gas or venting, or any wall or structural change needs a permit. 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. | FeeAbout $1,436 for a $35,000 project, when a permit is needed | ReviewNot published by the city | Cite verified 2026-04-29 |
| Bathroom remodel Depends on scope | Finish work, and swapping a prefabricated fixture without touching valves or pipes, need no permit. Moving plumbing, replacing a faucet, shower or tub valve, replacing a tub or shower or a site-built (tiled) shower, new circuits or wall changes need one, and so does finish work that alters a required accessible feature or is in a multiunit residential building (RCW 64.55). 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. | FeeAbout $999 for a $22,000 project, when a permit is needed | ReviewNot published by the city | Cite verified 2026-04-29 |
| Basement finish Always | Finishing or altering a basement is an alteration of the building and needs a permit. 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. | FeeAbout $1,579 for a $40,000 project | ReviewNot published by the city | Cite verified 2026-04-29 |
| Deck Depends on scope | A deck 30 in or less above grade and not over a story below needs no permit, attached or not, and neither does replacing decking boards alone. A higher deck, one over a story below, or any deck work in a critical area, a flood hazard area or a wildland-urban interface (WUI) location needs one. 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. | FeeAbout $841 for an $18,000 project, when a permit is needed | ReviewNot published by the city | Cite verified 2026-04-29 |
| Fence Depends on scope | A fence up to 6 ft located in accordance with the City's land use regulations and street standards needs no building permit unless the lot is in a flood hazard or critical area; taller, placed against those standards (zoning does not allow an electric or barbed-wire fence at all), or in such an area, it does. Fences not over 6 feet (1,829 mm) high are exempt. Maximum fence height per Mercer Island Permit FAQ: 6 feet. | FeeAbout $367 for a $6,000 project, when a permit is needed | ReviewNot published by the city | Cite verified 2026-04-29 |
| Siding Depends on scope | Replacing non-structural wood or vinyl siding needs no permit, even in a critical or flood hazard area. Other siding materials, veneer, stucco or EIFS, structural work, altering a required accessible feature, a multiunit residential building (RCW 64.55), or a wildland-urban interface (WUI) location needs one. 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. | FeeAbout $841 for an $18,000 project, when a permit is needed | ReviewNot published by the city | Cite verified 2026-04-29 |
| Window replacement Depends on scope | Replacing a window in kind needs no permit when no framing changes, egress is kept, safety glazing and fall protection are provided where required and the U-value meets the energy code, even in a critical or flood hazard area. A new or resized opening, a structural change, any of those conditions unmet, or a wildland-urban interface (WUI) location 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. | FeeAbout $446 for an $8,000 project, when a permit is needed | ReviewNot published by the city | Cite verified 2026-04-29 |
| Flooring Depends on scope | New flooring is finish work and needs no permit unless it alters an existing required accessible feature or the building is a multiunit residential building under RCW 64.55. Changing the subfloor or joists, or adding radiant heat, 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. | FeeAbout $367 for a $6,000 project, when a permit is needed | ReviewNot 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. | FeeAbout $4,496 for a $200,000 project | Review30–90 days | Cite verified 2026-05-16 |
| Roofing Depends on scope | In-kind re-roofing of a house needs no permit when the sheathing stays, even in a critical or flood hazard area. Replacing sheathing, changing the roofing material, framing work, or a wildland-urban interface (WUI) location needs a permit. 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. | FeeWhere a re-roof needs a permit on Mercer Island, re-roofing a single-family house is a $214 permit, except with the same roofing system or masonry tile (2026 Fee Schedule). | ReviewNot published by the city | Cite verified 2026-04-29 |
| HVAC Depends on scope | Installing or replacing heating, cooling or ventilation equipment needs a mechanical permit; portable appliances, minor part replacements and a self-contained unit with 10 lb of refrigerant or less and a motor of 1 hp or less do not, except outside the house's envelope in a flood hazard or critical area. 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. | FeeWith no building permit, Mercer Island prices a mechanical permit at its $46 issuance fee plus unit fees, $214 at the least: $29 for each furnace up to 100,000 Btu/h, $29 a compressor up to 3 horsepower, $20 an air handler up to 10,000 cfm, $46 a ventilation fan, and $24 for a repair or addition to a heating or cooling system. | ReviewNot published by the city | Cite verified 2026-04-29 |
| Electrical Always | The City of Mercer Island, not L&I, issues electrical permits, and its code exempts no electrical work: any installation, repair, replacement or maintenance of wiring or electrical equipment needs one. Mercer Island issues its own electrical permits — from the City's building official, not WA L&I. MICC 17.14.010 §105.1 requires anyone who intends to install, alter, repair, remove, convert or replace any electrical system to "first make application to the building official and obtain the required permit", and §105.1.2 requires an electrical permit, in accordance with chapter 19.28 RCW, for "The installation, alteration, repair, replacement, modification or maintenance of all electrical systems, wire and electrical equipment regardless of voltage." Mercer Island adopts the Washington Cities Electrical Code, Parts 1 and 3 (MICC 17.13.020), and its list of work exempt from permit (MICC 17.14.010 §105.2) has building, mechanical and plumbing items but no electrical ones. | FeeElectrical permit fees are the City of Mercer Island's, not an L&I fee. | ReviewNot published by the city | Cite verified 2026-09-25 |
| Plumbing Depends on scope | Stopping leaks, clearing stoppages, resetting a toilet and swapping a prefabricated fixture without changing valves or pipes need no permit. A water heater, new or moved fixtures, new piping, replacing concealed pipe, replacing a valve (a faucet included), or work on a site-built (tiled) shower or tub needs a plumbing permit. 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. | FeeWith no building permit, Mercer Island prices a plumbing permit at its $46 issuance fee plus unit fees, $214 at the least: $19 for each fixture, trap or set of fixtures, $9 a fixture for repairing or altering drain or vent piping, $24 a water heater, $12 a gas piping system and $44 a building sewer. | ReviewNot published by the city | Cite verified 2026-04-29 |
| Addition 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). | FeeAbout $3,223 for a $120,000 project | ReviewNot published by the city | Cite verified 2026-04-29 |
| Solar (rooftop PV) Always | A solar PV system needs a City electrical permit. A rooftop system on a house meeting every criterion of MICC 17.14.010 §105.2 Building item 22 needs no building permit. | FeeMercer Island's 2026 fee schedule has no residential solar line; its only solar fee is a commercial fire permit. | ReviewNot published by the city | Cite verified 2026-10-02 |
| Heat pump Depends on scope | Installing or replacing a heat pump needs a mechanical permit and a City electrical permit; a portable unit, a minor part replacement or a self-contained unit with 10 lb of refrigerant or less and a motor of 1 hp or less does not need the mechanical permit, except outside the house's envelope in a flood hazard or critical area. | FeeMercer Island prices a mechanical permit with no building permit at its $46 issuance fee plus unit fees, $214 at the least; the schedule names no heat pump, and counts each compressor up to 3 horsepower at $29 and each air handler up to 10,000 cfm at $20. | ReviewNot published by the city | Cite verified 2026-10-02 |
Ancillary & non-building permits
| Project | Threshold | Fee | Review days | Source |
|---|---|---|---|---|
| Demolition Always | Demolishing a building or structure needs a permit. 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. | FeeMercer Island's demolition permit is $430 for a single-family house and $214 for a soft or partial demolition; further plan review and inspection is $182 an hour (2026 Fee Schedule). | ReviewNot published by the city | Cite verified 2026-10-02 |
| Right-of-way Always | Any work in or occupation of the public right of way needs a right-of-way permit from the city, or from the agency that owns the street. 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. | FeeMercer Island's right-of-way use permit is $257 for a miscellaneous use, $342 for underground work in an unpaved area (Type A), $513 for surface improvements (Type B) and $769 for underground work in a paved area (Type C); an encroachment agreement is $769, and further review and inspection $182 an hour (2026 Fee Schedule). | ReviewNot published by the city | Cite verified 2026-09-07 |
| Side sewer Always | Building a side sewer or any modification of one needs the City's permit approvals first, with no minimum length. The City of Mercer Island requires its side sewer permit approvals before any construction of a side sewer or any modification of an existing one (MICC 15.06.040), so any repair counts, with no minimum length. A permit for work only on private property may go to the owner or a licensed side sewer contractor; work in a right-of-way or public sewer easement is permitted only to a licensed side sewer contractor. WAC 51-56, the state plumbing code, governs how the building sewer is laid. | FeeMercer Island's side sewer permit is $342 for a connection, a revision, modification or repair, a disconnect, or a stub-out to the property line; further review and inspection is $182 an hour (2026 Fee Schedule). | ReviewNot published by the city | Cite verified 2026-10-24 |
| 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. | FeeMercer Island's storm drainage review and inspection is billed hourly, $364 at the least (2 hours at $182); a land clearing permit is $214, and grading $285 for 50 to 100 cubic yards and $405 for 101 to 1,000. | ReviewNot 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). | FeeMercer Island's land use fees are minimums for a set number of staff hours, billed at $182 an hour beyond them: a variance is $11,830 (65 hours), a conditional use permit $19,110 plus hearing examiner costs, and a pre-application meeting $1,092 with up to 2 reviewers. | ReviewNot published by the city | Cite verified 2026-05-02 |
| Tree removal Depends on scope | On Mercer Island removing a tree needs a permit, a tree removal permit or approval within another construction permit, unless it is a small tree under 10 in across at 4.5 ft that is not an exceptional tree, or a species on the state or King County noxious, invasive or weeds of concern lists. An exceptional tree, a species the Exceptional Tree Table lists at its size: 6 in for a Pacific dogwood, madrona, Garry oak, Sitka spruce, Pacific yew, lodgepole pine, black hawthorn, Rocky Mountain maple or western serviceberry; 8 in for a cascara, vine maple or native willow; 9 in for a Washington hawthorn, the one nonnative species under 10 in, or any tree over 36 in or in a grove, needs one at any size. In a critical area or its buffer every tree needs one. Pruning on private property needs none; there is no yearly allowance. A tree in the street right-of-way is a street tree. Removing a tree on Mercer Island needs a permit approval, either a tree removal permit or approval within another construction permit, unless MICC 19.10.030 exempts it (MICC 19.10.020 B). Outside critical areas and their buffers and off public property, three things are exempt: removing a small tree, under 10 in across measured 4.5 ft above the ground, that is not an exceptional tree and was not planted as a replacement tree; removing a species on the state or King County noxious, invasive or weeds of concern lists; and pruning, as the code defines it, on private property (MICC 19.10.030, 19.16.010). An exceptional tree needs a permit at any size: a tree over 36 in, a tree in a grove (eight or more trees of 10 in or more forming a continuous canopy), or a tree at or over its species' size in the Exceptional Tree Table, as small as 6 in for a madrona, Pacific dogwood or Garry oak (MICC 19.16.010). In a critical area or its buffer every tree needs a permit, at any size. Removal includes cutting a tree, taking it out through site grading, and destroying roots so that it becomes hazardous. A tree posing an imminent threat to life or property may come down first, with the permit applied for within 14 days (MICC 19.10.020 B). A tree in the street right-of-way is a public tree: cutting or pruning one needs a tree permit, granted only on the code's criteria (MICC 19.10.100). | FeeMercer Island's single-family tree removal permit is $214 for 1 to 3 trees, $536 for 4 to 10 and $1,497 for more than 10; removing a tree outside a critical area with no development is $175, and within one $525 for 1 to 3 trees, plus the actual cost of any peer or geotechnical review. | ReviewNot published by the city | Cite verified 2026-10-27 |
| Signs Always | Putting up or structurally altering a permanent sign generally needs a city sign permit; which small or temporary signs are exempt differs by city. Each city's own sign code, usually a chapter of its zoning or development code, decides which signs need a permit and sets their size, number and placement by zone. Putting up or structurally altering a permanent sign generally needs a city sign permit, plus an electrical permit if the sign is lit, while repainting, ordinary maintenance and copy changes generally do not. Which small or temporary signs need no permit, and up to what size, differs from city to city, so check the city's own list before ordering a sign. | FeeMercer Island's design review of a sign by the Code Official is a $910 minimum fee, 5 hours of staff time, with more time at $182 an hour; a lit sign's electrical permit is $46 for a sign on one branch circuit, $9 for each more circuit, with the $46 issuance fee and $214 electrical minimum (2026 Fee Schedule). | ReviewNot published by the city | Cite verified 2026-05-02 |
Building in the City of Mercer Island?
Kolmo Construction is a licensed Washington general contractor — KOLMOL*753JS, bonded and insured — working throughout the City of Mercer Island and King County. We pull the building permits listed above and build the project. Electrical, plumbing and HVAC work, and those permits, go to licensed trade subcontractors that Kolmo manages.
How this page is built
Each row is the most-recently-verified authoritative rule on file for the City of Mercer Island and the listed project type. “Pending verification” means we have the 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.