Bolthole Index

King County, Washington

Building permits, zoning and septic rules in unincorporated King County, Washington

32Index Score / 100
#39 of 39 in Washington

Unincorporated King County, Washington requires building permits for construction, alteration, repair, demolition and occupancy changes, with limited exemptions for specified small projects outside critical areas1. King County administers zoning and building permits in unincorporated areas, while cities administer their own rules23. Public Health - Seattle & King County handles septic permits countywide4.

At a glance

Building permit
Required for most construction and alterations; listed small-project exemptions can disappear in critical areas1
Zoning
Yes; King County administers zoning in unincorporated areas, while cities administer their own rules2
Inspections
Required at project stages after King County issues a building permit5
Septic permit
Site application, design permit and installation permit required through Public Health - Seattle & King County46
Owner-builder exemption
Available from contractor registration, but not when building to sell, lease or demolish; permits still apply7
RV / tiny home occupancy
Overnight RV camping is allowed only in an approved campground; tiny houses need local approval89
Private well
A new or replacement well for a home and one ADU requires a King County application through a qualified professional10
Property tax
About 0.8% effective rate; median bill around $6,785/year1112

Who to call

Building permits

King County Permitting (Department of Local Services)

Issues land use, building, mechanical, and fire regulatory and operating permits for unincorporated King County

206-296-6600

permitquestions@kingcounty.gov

919 SW Grady Way, Suite 300, Renton, WA 98057

Online permits →

Septic permits

Public Health - Seattle & King County, Environmental Health Services

Reviews on-site sewage (septic) system site applications and issues installation permits for unincorporated King County; construction can't begin until the installation permit is posted on site

206-477-8050

Contact details are copied from each office’s official page and were checked against it on October 9, 2026.

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Do you need a building permit in unincorporated King County, Washington?

Yes. Unincorporated King County requires a building permit for construction, enlargement, alteration, repair, moving, demolition and occupancy changes1. Some common property improvements are exempt, but the county should confirm the specific project before work begins1. Applications deemed complete on or after March 15, 2024 use the 2021 Washington State Building Code with state and King County amendments13. King County requires a pre-construction conference for all new construction, inspections at project stages and visible work until approval; the permit holder must request each required inspection5. An owner working on their own property may be exempt from contractor registration, but not when building to sell, demolish or lease, and that exemption does not remove building, electrical, plumbing or land-use permit requirements7.

Who handles building permits in unincorporated King County, and how do you reach them?

King County Permitting issues building and land-use permits for unincorporated King County; each incorporated city administers its own zoning, land-use and building-permit rules3. Septic permits throughout King County remain with Public Health - Seattle & King County4. Call King County Permitting at 206-296-6600; phone service is available from 9 to 11 am and 12:30 to 2:30 pm on Monday, Tuesday, Thursday and Friday14. The office is at 919 SW Grady Way, Suite 300, Renton, WA 9805714. Most building and land-use applications can be filed through MyBuildingPermit.com, while some use email or another portal; online services include permit searches, status checks, fee payment and inspection scheduling15. The 2026 fee schedule runs through December 31, 2026, and most applications carry a $126 screening fee at submission16.

Does King County have zoning?

Yes. King County administers zoning in unincorporated areas, while each incorporated city administers its own zoning, land-use and permit rules23. In unincorporated King County, setbacks and building height vary by zoning district, and overlays or parcel-specific conditions can modify the base district171819. Construction lots generally cannot be smaller than 2,500 square feet in UR and R zones or 5,000 square feet in A, F and RA zones, subject to the stated exceptions and nonconforming-lot rules20. Lot creation and lot-line changes must also follow the county subdivision rules and zone-specific density provisions21. Most properties can support one accessory dwelling unit per primary detached dwelling or townhouse, but either the ADU or primary home must be owner-occupied22. A detached ADU requires a primary dwelling, the applicable zone minimum lot size and a notice filed on title before permitting, and is generally limited to 1,000 square feet of heated floor area23.

How do septic permits work in unincorporated King County?

Public Health - Seattle & King County administers on-site sewage permitting throughout King County4. A new system requires a site application, design permit and installation permit, and construction cannot begin until the installation permit is posted on the property6. Call Environmental Health Services at 206-477-8050; the septic technical voicemail is 206-477-817724. State rules also require a permit before installation, repair, modification, connection or expansion except for a minor repair; the local health officer responds within 30 days of a complete application, and a permit may last no more than five years25. A failed system within a sewer utility's service area must connect when the utility permits it and adequate sewer service is available within 200 feet along the usual or most feasible route26. Only about 0.5% of King County land is rated without severe limitations for a conventional drain field, so make septic feasibility an early purchase contingency27.

Can you live in an RV or tiny home on your land in King County?

Unincorporated King County allows overnight RV camping only in an approved campground; the county defines an RV as temporary living quarters for recreational camping, travel or seasonal use rather than a permanent dwelling8. An approved RV park limits a stay to 180 days during a 365-day period and must use a sewage system approved by Public Health - Seattle & King County8. A tiny house may be built on wheels and may contain up to 400 square feet, but it must comply with the Washington State Building Code and still needs local approval for its foundation, installation and location9. The RV-park rule does not itself say whether a single RV may serve as a long-term residence on private land outside a park, and King County's complete tiny-home occupancy rule also remains unconfirmed, so ask King County Permitting to review the parcel, proposed structure and intended use before purchase14. Zoning setbacks and height limits depend on the parcel's district1819.

Building a home in unincorporated King County: the steps, in order

  1. Confirm that the parcel is unincorporated and identify its zoning district, buildable lot status, setbacks and height limit3201819.
  2. Establish water: a home cannot be built or expanded without a source approved by Public Health - Seattle & King County or the state Office of Drinking Water28. A new or replacement private well serving one home and up to one ADU requires a county application through a certified septic designer or water-system engineer10.
  3. Have the septic designer submit the site application and secure design and installation permits before construction6.
  4. Submit building and land-use applications online where available and budget for the applicable fee guide plus the $126 screening fee charged on most applications1516.
  5. For flood-hazard construction, submit the required elevation certificate after the lowest floor is placed and before further vertical construction29.
  6. Request the pre-construction conference and each project-stage inspection, keeping work visible until approval5.

What to check before you buy land in unincorporated King County, Washington

Start with the usable building envelope, not total acreage. Only about 45.2% of King County land has a slope of 15% or less, while 83.1% is wooded, so clearing, access and grading can narrow the practical homesite3031. Only about 0.5% of the county is rated without severe limits for a conventional septic drain field, making septic feasibility an early due-diligence item27. Confirm the zoning district, legal lot status, subdivision history and any overlays before assuming acreage can be divided or built upon172120. Verify an approved water source, and if a private well is planned, account for county site review, water-quality documentation and pump testing2810. Flood-hazard projects require a lowest-floor-elevation inspection and an elevation certificate before further vertical construction3229. Budget around a 0.8% effective property-tax rate and a median annual bill near $6,7851112.

Watch-outs

  • Only about 0.5% of King County's land is rated free of severe limits for a conventional septic drain field -- get a site evaluation from Public Health - Seattle & King County before you count on a standard system2724.
  • A project that looks minor may still need a King County building permit; confirm the specific exemption and whether critical areas or other site conditions apply before work begins1.
  • Overnight RV camping in unincorporated King County is allowed only in an approved campground, and no rule we could confirm authorizes living in an RV on an ordinary parcel; ask King County Permitting before buying land for that purpose83314.

Sources

  1. Permits, quoted and re-checked
  2. About King County zoning, quoted and re-checked
  3. About King County zoning, quoted and re-checked
  4. On-site sewage/septic system program, quoted and re-checked
  5. Building and fire inspections, quoted and re-checked
  6. New design and installation, quoted and re-checked
  7. RCW 18.27.090 - Exemptions, quoted and re-checked
  8. aqua.kingcounty.gov, quoted and re-checked
  9. Tiny Houses (Washington statewide rule), quoted and re-checked
  10. Creating or replacing a water system, quoted and re-checked
  11. Effective property tax rate: Bolthole Index county data
  12. Median property tax bill: Bolthole Index county data
  13. Building and fire codes, quoted and re-checked
  14. King County Permitting (Department of Local Services) (kingcounty.gov)
  15. Permits, quoted and re-checked
  16. Permit fees - Building and land use, quoted and re-checked
  17. Title 21A - Zoning, quoted and re-checked
  18. kingcounty.gov, quoted and re-checked
  19. Title 21A - ZONING, quoted and re-checked
  20. Title 21A - Zoning, quoted and re-checked
  21. aqua.kingcounty.gov, quoted and re-checked
  22. kingcounty.gov, quoted and re-checked
  23. kingcounty.gov, quoted and re-checked
  24. Public Health - Seattle & King County, Environmental Health Services (kingcounty.gov)
  25. WAC 246-272A-0200 Permit requirements (Washington statewide rule), quoted and re-checked
  26. WAC 246-272A-0025 — Connection to public sewer system (Washington statewide rule), quoted and re-checked
  27. Share of soils USDA rates "not limited" for a conventional septic drain field (SSURGO). A strict rating: the median county is about 6% and a tenth of counties are 0%, so a low figure means most lots need a site evaluation or an engineered system, not that septic is impossible. Cite it only with that caveat: Bolthole Index county data
  28. Permitting process, quoted and re-checked
  29. Title 16 - Building and Construction Standards, quoted and re-checked
  30. Share of land at 15% slope or less: Bolthole Index county data
  31. Wooded share of land: Bolthole Index county data
  32. Building and fire inspections, quoted and re-checked
  33. Title 21A - Zoning, quoted and re-checked

Written October 9, 2026 from the rules quoted below, each taken from an official source and re-checked by an independent reviewer. This is research, not legal advice: rules change, so confirm with the office before you buy or build.

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Compared with neighboring counties

Like all 6 of its neighbors, King County has countywide zoning.

RuleKing CountyPierce CountyKitsap CountySnohomish CountyIsland CountyThurston CountyMason County
Building permitRequiredRequiredLimitedRequiredRequiredRequiredRequired
County zoningYesYesYesYesYesYesYes
Septic permitsPublic HealthTacoma-Pierce County Health Dept.Kitsap Public Health DistrictCounty Health Dept.County Public HealthCounty Public Health & Social ServicesCounty Community Services

County locator

King County in Washington

32
County map
King County highlighted among the Washington counties · colored by Index score

How King County scores

Seclusion14100% ev.
Self-Sufficiency34100% ev.
Admin Boringness41100% ev.
Durability53100% ev.
Property Autonomy50100% ev.
Carry Cost30100% ev.

Evidence strength: 100%. This reports direct-source completeness and fallback use; it is separate from the score and is not a confidence interval. How it works →

$858kTypical home
0.8%Property tax
$38,716Land / acre
75.4"Annual rain
4.8% of yrsSevere drought
0.2 / yr (+0.2)Mid-century 100°F days
20 daysMid-century dry spell
2.5" (+8.5%)Mid-century 1-day rain
1.45×Wildfire change factor
100%Forward climate coverage
$1,505Home insurance / yr
2.2% / yrInsurance growth
0.64%Nonrenewal rate
county median (2+ published ZIPs)Insurance basis
1,271,004People within 30 min
5,206,293People within 2 hr
939,814Radius comparison (15 mi)
1,073.8People / sq mi
28.5%Federal land
45.2%Land at 15% slope or less
0.5%Soils rated "not limited" for septic (strict USDA rating)
6,608 acWorkable land screen
83.1%Wooded land
108.1 tonsBiomass / forest ac
47.9°FAvg temp

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Cities and towns in King County

Inside a city or town, that city usually issues building permits and sets zoning; the county’s rules above cover unincorporated land. Septic, wells and floodplain rules usually stay with the county or state everywhere.

Not yet researched: Algona · Auburn · Black Diamond · Carnation · Enumclaw · Kent · Medina · Mercer Island · Sammamish

Answers from the rulebook for King County

What the ordinances and state agencies actually say — one answer per question, each quoted from the official source and independently re-checked.

King County rules

  • Building permitRequired

    Building or structure projects in unincorporated King County involving occupancy changes, construction, enlargement, alteration, repair, moving, or demolition.

    • A permit is not required, unless the property contains critical areas, for a storage shed with a floor area of 200 square feet or less as an accessory to a residential house or for agricultural use.
    • A permit is not required, unless the property contains critical areas, for fences 6 feet high or less.
    • A permit is not required, unless the property contains critical areas, for most retaining walls 4 feet high or less.
    • A permit is not required, unless the property contains critical areas, for replacement of roofing or siding for detached one- and two-family houses.
    • A permit is not required, unless the property contains critical areas, for uncovered decks 30 inches or less above the ground.
    • A permit is not required, unless the property contains critical areas, for interior finishes such as carpet, hardwood flooring, tile, paint, and wallpaper.
    • A permit is not required, unless the property contains critical areas, for replacing windows with new windows.
    • A permit is not required, unless the property contains critical areas, for replacing doors with new doors.
    • A permit is not required, unless the property contains critical areas, for roof-mounted solar photovoltaic panels weighing less than 4 pounds per square foot on residences.
    • Special conditions that may require permits include critical areas, established clearing limits, flood zones, historically sensitive areas, setback areas, shorelines, steep slopes, total impervious lot coverage, and wetlands.
    • Requirements may differ in incorporated municipalities.

    storage shed floor area exemption: <= 200 square feet (Only when accessory to a residential house or for agricultural use, and unless the property contains critical areas.) · fence-height exemption: <= 6 feet (Unless the property contains critical areas.) · retaining-wall exemption: <= 4 feet (Most retaining walls; unless the property contains critical areas.) · uncovered-deck exemption: <= 30 inches above ground (Unless the property contains critical areas.) · roof-mounted residential solar photovoltaic panel weight exemption: < 4 pounds per square foot (Unless the property contains critical areas.)

    “Permits we offer in unincorporated King County [...] Apply for a building permit if your project includes any of the following on a building or structure: Changing the occupancy Constructing Enlarging Altering Repairing Moving Demolishing”
    One more reviewed finding on this topic
    • Required — Building and structure construction, alteration, repair, movement, demolition, or occupancy changes in unincorporated King County.
      “you need a building permit to [...] construct [...] a building or structure.”
  • Building code adoptedAdopted (with conditions)

    Applications deemed complete on or after March 15, 2024, in unincorporated King County.

    • The 2021 Washington State Building Code applies with Washington amendments and King County Code amendments in Titles 16 and 17.
    • Applications deemed complete on or after February 1, 2021 and before March 15, 2024 use the 2018 State Building Codes.

    code edition: 2021 (Applications deemed complete on or after 2024-03-15)

    “King County is currently enforcing the 2021 State Building Codes.”
    One more reviewed finding on this topic
    • Partial — Energy-efficiency inspections for buildings in unincorporated King County.
      “Energy efficiency inspections shall be in accordance with the International Energy Conservation Code, as adopted and amended by chapters 51-11C and 51-11R WAC, and as amended in this title.”
  • InspectionsRequired

    Projects for which King County issues a building permit.

    • Inspections occur at different stages.
    • Work must remain visible and available for inspection until completed and approved.
    • The permit holder must contact King County Permits to request required inspections.
    • Actual inspection types vary by project scope.
    • A pre-construction conference is required for all new construction and must be requested before work begins.
    “After King County issues a building permit, inspections are required at different stages of the project.”
    One more reviewed finding on this topic
    • Required — Construction performed under a King County building permit.
      “After King County issues a building permit, inspections are required at different stages of the project.”
  • County-wide zoningPresent

    Zoning, land use, and permitting in unincorporated King County.

    • Incorporated cities have jurisdiction over their own zoning, land use, and permits.
    “Each city in King County has jurisdiction over their own zoning, land use and permits while King County manages zoning, land use and permits for unincorporated areas in the county.”
    One more reviewed finding on this topic
    • Present (with conditions) — King County zoning under Title 21A in unincorporated King County.
      “The purpose of this chapter is to establish basic dimensional standards for development relative to residential density and as well as specific rules for general application. The standards and rules are established to provide flexibility in project design, and maintain privacy between adjacent uses.”
  • Local zoningVaries (with conditions)

    Aggregate local zoning across King County, where incorporated cities administer their own zoning and King County administers zoning in unincorporated areas.

    • The conclusion aggregates separate local jurisdictions; the county does not administer each incorporated city's zoning ordinance.
    • Incorporated cities have jurisdiction over their own zoning, land use and permits.
    • King County manages zoning, land use and permits for unincorporated areas.
    “Each city in King County has jurisdiction over their own zoning, land use and permits while King County manages zoning, land use and permits for unincorporated areas in the county.”
    One more reviewed finding on this topic
    • Varies (with conditions) — Aggregate local zoning across King County, including incorporated cities and unincorporated areas.
      “Each city in King County has jurisdiction over their own zoning, land use and permits while King County manages zoning, land use and permits for unincorporated areas in the county.”
  • Zoning districtsPublished (with conditions)

    Zoning classifications and zoning map symbols in unincorporated King County.

    • Title 21A identifies Agricultural, Forest, Mineral, Rural Area, Urban Reserve, Urban Residential, Neighborhood Business, Community Business, Regional Business, Office, and Industrial classifications.
    • Property-specific development standards, special district overlays, potential zones, and interim zones may modify or supplement the base classification.
    “Resource zones [Agricultural (A), Forestry (F), or Mining (M)]”
    One more reviewed finding on this topic
    • Published (with conditions) — Published zoning districts and permitted-use tables for unincorporated King County.
      “To find out what you can build, or how you can use your property, consult the Land Use Tables in the Permitted Uses chapter of the King County Code, K.C.C.21A.08.”
  • Minimum lot sizeDistrict specific (with conditions)

    Construction lots in the UR, R, A, F, and RA zoning areas of unincorporated King County.

    • Except for nonconformances in K.C.C. 21A.32, no construction is permitted in UR and R zones on a lot smaller than 2,500 square feet or lacking the applicable minimum lot width.
    • Exceptions in UR and R zones include townhouse developments, zero-lot-line subdivisions, and lots created before February 2, 1995 in a recorded subdivision or short subdivision that complied with applicable laws.
    • In A, F, or RA zones, construction is not permitted on a lot smaller than 5,000 square feet.
    • In A, F, or RA zones, lots greater than 5,000 square feet but less than 12,500 square feet are limited to one dwelling unit and residential accessory uses.

    minimum lot area in UR and R zones: >= 2500 square feet (subject to stated exceptions and K.C.C. 21A.32 nonconformances) · minimum lot area in A, F, and RA zones: >= 5000 square feet (construction is not permitted below this threshold) · one-dwelling-unit threshold in A, F, and RA zones: greater than 5,000 and less than 12,500 square feet (limited to one dwelling unit and residential accessory uses)

    “In the UR and R zones no construction shall be permitted on a lot that contains an area of less than 2,500 square feet [...] In the A, F or RA zones: 1. Construction shall not be permitted on a lot containing less than 5,000 square feet;”
  • SetbacksDistrict specific (with conditions)

    Setbacks for zoning districts in unincorporated King County.

    • The county directs applicants to the K.C.C. 21A.12 tables.
    • Minimum street and interior setbacks vary by zone.
    • Additional development conditions may apply.
    • Regional utility corridors, alleys, neighboring nonconforming setbacks, proposed use, and permitted projections may affect setbacks.
    “Find the setbacks for your zone in the Densities and Dimensions section of the King County Code, K.C.C.21A.12.”
  • Building heightSpecified

    Building-height controls under King County Title 21A in unincorporated King County.

    • Actual height limits vary by applicable zone.
    • Height is measured from average finished grade to the highest point of the roof.
    • Berms are excluded from the average finished-grade calculation.
    “Base Height (11a) 35 ft 35 ft 35 ft 60 ft 60 ft 60 ft 60 ft”
  • Living in an RVTemporary only (with conditions)

    Recreational-vehicle occupancy and overnight camping in unincorporated King County.

    • King County defines a recreational vehicle as designed primarily not for use as a permanent dwelling unit but as temporary living quarters for recreational camping, travel or seasonal use.
    • Overnight camping is allowed only in an approved campground.
    • Recreational vehicle parks are subject to a maximum stay of 180 days during a 365-day period.
    • The minimum distance between recreational vehicle pads is 10 feet.
    • Sewage must be disposed in a system approved by Public Health - Seattle & King County.

    maximum length of stay: 180 days during a 365-day period · minimum distance between recreational vehicle pads: >= 10 feet

    “Overnight camping is allowed only in an approved campground. [...] The maximum length of stay of any vehicle shall not exceed one hundred eighty days during a three-hundred-sixty-five-day period;”
    One more reviewed finding on this topic
    • Temporary only (with conditions) — Recreational vehicle parks in unincorporated King County; the code defines such parks as land with two or more recreational-vehicle sites for temporary living quarters for recreation or vacation purposes.
      “Recreational vehicle parks are subject to the following conditions and limitations: a. The maximum length of stay of any vehicle shall not exceed one hundred eighty days during a three-hundred-sixty-five-day period; b. The minimum distance between recreational vehicle pads shall be no less than ten feet; and c. Sewage shall be disposed in a system approved by public health - Seattle & King County.”
  • Accessory dwellingsAllowed (with conditions)

    Accessory dwelling units in unincorporated King County.

    • Generally one ADU is allowed per primary detached dwelling or townhouse unit.
    • Either the ADU or primary dwelling must be owner-occupied.
    • Detached ADUs require one primary dwelling and applicable lot-size thresholds.
    • Detached ADU thresholds listed by the county include UR/R: 5,000 square feet; RA-2.5: 1.875 acres; RA-5: 3.75 acres; RA-10: 7.5 acres; RA-20: 15 acres; A-10: 10 acres; A-35: 35 acres.
    • A detached ADU may be allowed on a 2.5-acre RA-5 parcel if the owner purchases a transferable development right.
    • ADUs are generally limited to 1,000 square feet heated and 1,000 square feet unheated floor area, subject to stated exceptions.
    • No additional off-street parking space is required.
    • An applicant must file the required notice before beginning the permitting process.

    UR/R detached ADU minimum lot size: 5000 sq ft · RA-2.5 detached ADU minimum lot size: 1.875 acres · RA-5 detached ADU minimum lot size: 3.75 acres (2.5 acres with a transferable development right) · RA-10 detached ADU minimum lot size: 7.5 acres · RA-20 detached ADU minimum lot size: 15 acres · A-10 detached ADU minimum lot size: 10 acres · A-35 detached ADU minimum lot size: 35 acres

    “Only one ADU is allowed per primary detached dwelling unit [...]”
    One more reviewed finding on this topic
    • Allowed (with conditions) — Accessory dwelling units in unincorporated King County.
      “Most properties in Unincorporated King County can support an Accessory Dwelling Unit”
  • Who permits septicLocal (with conditions)

    On-site sewage and septic systems in King County.

    • Public Health–Seattle & King County provides permitting, education, and professional certification services.
    • State rules and county codes may also apply.
    “We also provide permitting and educational services for septic system owners”
    2 more reviewed findings on this topic
    • Local — On-site sewage permitting and related wastewater applications in King County.
      “Submit an application for the below wastewater permits through the Public Health Permit Center.”
    • Local (with conditions) — On-site sewage systems in King County administered by Public Health - Seattle & King County.
      “submits a site application to Public Health - Seattle & King County.”
  • Septic permitRequired

    Construction of a new on-site sewage system in King County.

    • A site application, design permit, and installation permit are required.
    • Construction must not begin until the installation permit is posted on the site or property.
    • The site application is submitted to Public Health - Seattle & King County.
    • The application may be appealed through the Sewage Review Committee; appeals must be filed by 3 p.m. within 60 calendar days from the decision or order date.
    “A site application design and installation permit are required when a new on-site sewage system is constructed. Construction must not begin until the installation permit is posted on the site/property.”
    2 more reviewed findings on this topic
    • Required — Wastewater and onsite sewage applications administered through the Public Health Permit Center.
      “Submit an application for the below wastewater permits through the Public Health Permit Center.”
    • Required — Construction of a new onsite sewage system in King County.
      “A site application design and installation permit are required when a new on-site sewage system is constructed. Construction must not begin until the installation permit is posted on the site/property.”
  • Well permitRequired

    New or replacement private wells serving a single-family residence and up to one accessory dwelling unit on the same property.

    • Application must be submitted through a certified onsite sewage system designer or water-system engineer.
    • Public Health inspects the proposed well site and reviews water-quality and pump-test documentation.
    • A licensed well driller must comply with chapter 173-160 WAC.
    • A two-hour pump test is required; if flow is 5 gpm or less, a four-hour test and proof of at least 400 gallons per day are required.

    low-flow threshold: <= 5 gpm (requires a 4-hour pump test and proof of at least 400 gallons per day) · pump test: 2 hours (4 hours if flow rate is 5 gpm or less)

    “Private wells serving a single-family residence and up to one ADU on the same property must apply to King County”
  • Mandatory utility hookupConditional

    Homes and onsite sewage systems seeking development approval in King County.

    • Homes cannot be built or expanded without water from an approved water source.
    • Approved water sources are approved by either Public Health – Seattle & King County or the Washington State Department of Health’s Office of Drinking Water.
    • This source does not establish a universal requirement to connect to public sewer.
    “On-site sewage systems or homes cannot be built or expanded if they don’t have water from an approved water source.”
  • Subdividing landRegulated (with conditions)

    Subdivision and land division in unincorporated King County.

    • Applicants must determine zoning and consult K.C.C. 21A.12 density and dimensions provisions.
    • Residential, rural, resource, commercial, and industrial zones use different density tables.
    • Rural-area calculations have special rounding rules.
    “Creation of or changes to lot lines shall conform with [...] Title 19, Subdivisions.”
  • Building in a floodplainLimited

    Building inspections for projects in flood-hazard areas in unincorporated King County.

    • A lowest-floor-elevation inspection is listed for projects in flood-hazard areas.
    • This evidence establishes an inspection condition, not a complete floodplain-development permit regime.
    “Lowest floor elevation (for projects in flood hazard areas)”
    One more reviewed finding on this topic
    • Required — Building construction in flood hazard areas subject to King County Title 16.
      “In flood hazard areas, upon placement of the lowest floor, including the basement, and before further vertical construction, the elevation certificate required in section IBC 1612.4 and in K.C.C. chapter 21A.24 shall be submitted to the building official.”
  • Permit feesPublished (with conditions)

    King County building and land-use permit fees for unincorporated King County.

    • 2026 fees apply January 1 through December 31, 2026.
    • Most permit-related fees increase by about 14% on January 1, 2026.
    • An application screening fee of $126 applies to most permit applications when submitted.
    • Detailed fees vary by permit type and fee guide.

    application screening fee: 126 USD (most permit applications) · fee schedule period: 2026-01-01 to 2026-12-31

    “an application screening fee of $126 will be applied to most permit applications”
  • Permit processPublished (with conditions)

    King County building, land-use, septic-related intake, payment, and inspection processes.

    • Most building and land-use permits can be applied for online through MyBuildingPermit.com.
    • Some permit types must be submitted by email or through other portals.
    • Permit applications involving septic systems may require an approved septic permit and site plan or application submittal.
    • The permit portal supports status checks, record details, fee payment for non-MyBuildingPermit permit types, permit searches, and inspection scheduling.
    “Find step-by-step instructions on kingcounty.gov’s Local Services pages”
    One more reviewed finding on this topic

Washington rules that apply here

  • Owner-builder exemptionConditional

    An owner or other person performing construction-related contractor activities on the person's own property or personal residence under Washington contractor-registration law.

    • The exemption concerns registration provisions under chapter 18.27 RCW and does not itself eliminate applicable building, electrical, plumbing, mechanical, land-use, or inspection requirements.
    • For work on the person's own property, the exemption does not apply when the person performs contractor activities for the purpose of selling, demolishing, or leasing the property.
    • For an owner contracting with a registered contractor, the exemption does not apply to a person performing contractor activities to lease or sell improved property owned for less than twelve months.

    small-project contract threshold: < 500 USD (The threshold exemption does not apply when the work is part of a larger operation, contracts are divided to evade the chapter, or the person advertises as a contractor.)

    “The registration provisions of this chapter do not apply to: [...] (12) Any person working on his or her own property, whether occupied by him or her or not, and any person working on his or her personal residence, whether owned by him or her or not but this exemption shall not apply to any person who performs the activities of a contractor on his or her own property for the purpose of selling, demolishing, or leasing the property;”
    2 more reviewed findings on this topic
    • Conditional — Contractor-registration requirements for persons working on their own property or personal residence in Washington, including King County.
      “The registration provisions of this chapter do not apply to:”
    • Available (with conditions) — A person working on their own property or personal residence under Washington contractor-registration law.
      “The registration provisions of this chapter do not apply to:”
  • Minimum dwelling sizeSpecified

    Dwelling units regulated by Washington's state building code.

    • The rule specifies habitable-space and room-area minimums, not a zoning minimum lot or gross floor-area standard.
    • Kitchens are expressly excepted from the minimum floor-area requirement.
    • Efficiency dwelling units must comply with Sections 1208.1 through 1208.4 and must have a separate closet, required kitchen facilities, light and ventilation, and a separate bathroom as stated in the source.
    • The current rule text states WSR 23-23-102 was filed 11/15/23 and effective 3/16/24.

    minimum habitable space: >= 190 square feet · minimum area of at least one room: >= 120 square feet · minimum net floor area of sleeping units and other habitable rooms: >= 70 square feet (Kitchens are not required to be of a minimum floor area.)

    “1208.3 Dwelling unit size. Dwelling units shall have a minimum of 190 square feet (17.7 m 2) of habitable space. 1208.4 Room area. Every dwelling unit shall have not less than one room that shall have not less than 120 square feet (11.2 m 2) of net floor area. Sleeping units and other habitable rooms of a dwelling unit shall have a net floor area of not less than 70 square feet (6.5 m 2). EXCEPTION: Kitchens are not required to be of a minimum floor area.”
  • Tiny homesAllowed (with conditions)

    Occupancy and placement of tiny houses in Washington

    • A tiny house may be built on wheels and may not exceed 400 square feet including kitchen, bathroom, and sleeping/living area.
    • It must be built to the Washington State Building Code.
    • Approval depends on where it is built; local building-department requirements and permits apply to foundation, installation, and location.
    • A wheeled structure that is not a tiny house as described may instead be a recreational vehicle or park model.
    • A manufactured home, including a tiny manufactured home, requires consultation with the local building department regarding where it may be located.

    maximum area: <= 400 square feet

    “A tiny house is a dwelling that may be built on wheels and is no larger than 400 square feet, including a kitchen, bathroom, and sleeping/living area, and must be built to the Washington State Building Code. The approval process for a tiny house depends on where it's built.”
  • Manufactured homesLimited

    State statutory limits on county regulation of the placement or use of HUD-standard manufactured homes in Washington; site-specific occupancy remains subject to applicable local and state requirements.

    • The nondiscrimination and equal-siting rule applies to homes built to 42 U.S.C. Sec. 5401-5403 standards, as amended in 2000.
    • Except as provided in RCW 36.01.225(2), a county may require that a manufactured home be new.
    • Except as provided in RCW 36.01.225(2), a county may require a permanent foundation specified by the manufacturer and enclosure of the space from the bottom of the home to the ground with concrete or an approved concrete product, load bearing or decorative.
    • Except as provided in RCW 36.01.225(2), a county may require compliance with local design standards applicable to all other homes in the neighborhood.
    • Except as provided in RCW 36.01.225(2), a county may require thermal equivalence to the state energy code and all other requirements for a designated manufactured home under RCW 35.63.160.
    • A county may not restrict location in a manufactured/mobile home community legally in existence before June 12, 2008, based exclusively on the manufactured/mobile home's age or dimensions.
    • A county may not prohibit siting on an existing lot solely because existing separation and setback requirements regulating distance between homes are unmet.
    • A county may restrict location in a manufactured/mobile home community for other reasons, including failure to comply with fire, safety, other local ordinances, or state laws related to manufactured/mobile homes.
    • The statute does not override legally recorded covenants or deed restrictions of record and does not affect authority granted under chapter 43.22 RCW.

    community legal-existence date for age-or-dimensions protection: 2008-06-12 (Applies to manufactured/mobile home communities legally in existence before this date.)

    “A county may not adopt an ordinance that has the effect, directly or indirectly, of discriminating against consumers' choices in the placement or use of a home in such a manner that is not equally applicable to all homes. Homes built to 42 U.S.C. Sec. 5401-5403 standards (as amended in 2000) must be regulated for the purposes of siting in the same manner as site built homes, factory built homes, or homes built to any other state construction or local design standard.”
  • Septic inspectionRequired

    On-site sewage systems for all activities requiring an OSS permit statewide.

    • The local health officer or an authorized inspector must coordinate access before inspection.
    • If the owner does not authorize access, the local health officer may use administrative search-warrant procedures under RCW 70A.105.030.
    • For a single-property OSS serving one dwelling unit on that property, an inspection and maintenance easement may not be required as a permit condition.
    • During final construction inspection, the local health officer or OSS designer must confirm the OSS meets the approved design.
    • Required inspections must include the minimum tank, lid/access/riser, OSS/reserve-area, component, record-drawing, and proprietary-product review items stated in WAC 246-272A-0260(5).
    “(1) For all activities requiring a permit, the local health officer shall inspect the OSS.”
  • Agricultural exemptionAvailable (with conditions)

    Temporary growing structures used solely for production of horticultural plants in Washington.

    • The exemption is limited to temporary growing structures.
    • The structures must be used solely for production of horticultural plants, including ornamental plants, flowers, vegetables, and fruits.
    • The statute states that a temporary growing structure is not considered a building or structure for purposes of chapter 19.27 RCW.
    • This is not a general exemption for residences or all agricultural buildings.
    “The provisions of this chapter do not apply to temporary growing structures used solely for the production of horticultural plants including ornamental plants, flowers, vegetables, and fruits. A temporary growing structure is not considered a building or structure for purposes of this chapter.”
  • Driveway accessRequired

    Approaches or driveway connections from abutting property to Washington county roads.

    • Permission must be obtained from the county board before construction.
    • Counties may adopt reasonable approach-construction rules, including culvert, fill-depth, and drainage requirements.
    • Construction must be supervised by the county road engineer and paid for by the person benefited.
    • Violation is a misdemeanor.
    “No person shall be permitted to build or construct any approach to any county road without first obtaining permission therefor from the board.”
    One more reviewed finding on this topic
    • Required — Approach roads and driveway connections constructed on Washington state highway rights-of-way.
      “No person, firm, or corporation may be permitted to build or construct on state highway rights-of-way any approach road or any other facility, thing, or appurtenance not heretofore permitted by law, without first obtaining written permission from the department.”
  • Campground & park staysLimited

    Recreational vehicles in the context of Washington's manufactured/mobile-home community statutes

    • The rule defines an RV as temporary and transient living quarters.
    • The RV is not occupied as a primary residence.
    • The RV is not immobilized or permanently affixed to a manufactured/mobile home lot.
    • This claim does not establish general statewide siting permission on private land; local land-use and building rules may apply.
    “(12) "Recreational vehicle" means a travel trailer, motor home, truck camper, or camping trailer that is primarily designed and used as temporary living quarters, is either self-propelled or mounted on or drawn by another vehicle, is transient, is not occupied as a primary residence, and is not immobilized or permanently affixed to a manufactured/mobile home lot.”
    One more reviewed finding on this topic
    • Limited — Camping and temporary occupancy in Washington State Parks facilities
      “The maximum length of stay shall be no more than 10 nights in one park within a 30-day period. Total nights stayed by the same camping party must not exceed 90 nights per calendar year in all state parks. These limitations shall not apply to those individuals who meet the qualifications of WAC 352-32-280 and 352-32-285.”
  • county zoning authorityGeneral

    Washington counties adopting zoning and related official controls for county jurisdiction, including unincorporated areas.

    • A county must create a planning agency as authorized in RCW 36.70.030 and RCW 36.70.040 before engaging in the chapter's planning program.
    • Zoning maps may be adopted only for areas covered by a comprehensive plan containing at least a land use element and a circulation element.
    • Zoning regulations may address land uses, building location and dimensions, yards and open spaces, population density, lot coverage, parking, and minimum gross floor area requirements for single-family detached dwellings.
    • The cited enabling provisions do not state a population threshold, named-county limitation, or special geographic limitation.
    “Any board, by ordinance, may establish classifications, within each of which, specific controls are identified, and which will regulate:”
    One more reviewed finding on this topic
    • General — Washington counties may plan and adopt zoning and other official controls for county land, including unincorporated areas, through their boards and planning agencies.
      “Such official controls may include, but are not limited to, ordinances establishing zoning, subdivision control, platting, and adoption of detailed maps.”
  • county building authorityGeneral

    Washington counties requiring and enforcing building permits and adopting amendments to the state building code for residential construction within county jurisdiction, including unincorporated areas.

    • The state building code must be enforced by counties and cities within their jurisdictional boundaries.
    • A county without a building department must contract with another county, city, or approved inspection agency for enforcement.
    • County amendments may not diminish the minimum performance standards and objectives of the state building code.
    • Residential-building amendments are subject to approval by the state building code council under RCW 19.27.074(1)(b), except as provided by statute.
    • The building-permit definition incorporates exemptions in International Building Code section 105.2 and International Residential Code section R105.2.
    • Counties may adopt permit exemptions for certain specified R-3 or M-1 construction or alteration with total fair market value not exceeding $1,500, but the exemption does not remove substantive code standards.

    permit-exemption fair-market-value ceiling: <= 1500 USD (Applies only to certain construction or alteration of group R, division 3, or group M, division 1 occupancies under RCW 19.27.060(7); substantive code standards still apply.)

    “The state building code required by this chapter shall be enforced by the counties and cities. Any county or city not having a building department shall contract with another county, city, or inspection agency approved by the county or city for enforcement of the state building code within its jurisdictional boundaries.”

Still unanswered

We looked and could not find an official answer yet. Silence is not permission — ask the county directly.

  • Lot coverage — Lot coverage or impervious-surface limits by zoning district.
  • Camping on your land — Temporary camping on private land in unincorporated King County.
  • Off-grid sanitation — Off-grid sanitation and alternatives to connection to public sewer.
  • Short-term rentals — Short-term rental use in unincorporated King County.

Each answer was extracted from an official source and independently re-checked against that source by a second reviewer. That is an evidence check, not legal advice. Rules change; confirm with the authority before you buy or build.

Water rights & wells in King County

Whether a new home can legally get its own water here — the sub-state groundwater regime, from Washington’s water agency.

Over-appropriated / declining

The aquifer here is over-appropriated and declining. A domestic well is usually still permit-exempt, but long-term supply is a genuine risk.

Household wellExempt up to a limit

RCW 90.44.050 exempts up to 5,000 gpd for domestic use, but the 2018 Streamflow Restoration Act caps NEW permit-exempt domestic wells at 3,000 gpd/connection in some basins and 950 gpd (350 gpd indoor in drought) in others, and new post-2020 wells in the adjudicating Nooksack basin are limited to ~500 gpd indoor.

Limit: 5,000 gpd base (RCW 90.44.050); capped to 3,000 or 950 gpd/connection in streamflow-restoration basins; ~500 gpd indoor for new Nooksack wells

Washington Dept of Ecology — Groundwater permit exemption ↗
  • Streamflow Restoration 950-gpd basins (RCW 90.94.030)partial of county

    New permit-exempt domestic wells capped at a maximum annual-average 950 gpd per connection, curtailable to 350 gpd indoor-only during a declared drought emergency.

    Washington Legislature — RCW 90.94.030 ↗

Hybrid state (appropriation + riparian). Groundwater rules change and basin boundaries follow the aquifer, not the county line — confirm current well and appropriation rules with the Washington state water agency before you buy or drill.Groundwater governance as of Jul 2026, cited to each administering agency.

Living off-grid in King County, Washington

Is King County a good place to live off-grid or homestead?

King County scores 32/100 on the Bolthole Index, a marginal county profile. Watch-outs: little seclusion — roughly 1,271,004 people within a 30-minute drive and higher long-term carry cost.

Do you need a building permit in King County, Washington?

King County generally requires a residential building permit, and it enforces county zoning. Onsite septic is permitted by Public Health - Seattle & King County (On-site Sewage System program). Owner-builders may act as their own contractor to build their home. These answers are quoted from official sources and independently re-checked. Rules change and cities within the county differ — always confirm with the county before you buy or build.

Can you live in an RV or tiny home on your land in King County?

Living in an RV on your own land in King County is allowed on a temporary basis only: Recreational-vehicle occupancy and overnight camping in unincorporated King County. King County defines a recreational vehicle as designed primarily not for use as a permanent dwelling unit but as temporary living quarters for recreational camping, travel or seasonal use. Overnight camping is allowed only in an approved campground. A tiny home is allowed. Confirm with the county before relying on it.

How much does land cost in King County, Washington?

Land in King County runs about $38,716 per acre, based on the latest county data.

What is the water situation in King County?

King County gets about 75.4" of rain a year, with severe drought in roughly 4.8% of years. On water rights, King County lies in the Streamflow Restoration 950-gpd basins (RCW 90.94.030) — New permit-exempt domestic wells capped at a maximum annual-average 950 gpd per connection, curtailable to 350 gpd indoor-only during a declared drought emergency..

How remote is King County?

A representative private-land location has about 1,271,004 people within a 30-minute drive and 5,206,293 within two hours. The road-network catchments count population across county lines and clusters of smaller cities; straight-line radius values remain available as a comparison.

How King compares in Washington

Compare side-by-side →See all 39 Washington counties ranked →