Tiny House Zoning in Washington State

Adams County, in central Washington centered on Ritzville, offers agricultural plains and minimal regulatory oversight. The county administers basic zoning in unincorporated areas, while Ritzville, Othello, Lind, Washtucna, and Hatton run their own codes. In county areas, tiny houses on permanent foundations can proceed if they meet state septic requirements through the health district. Minimum square footage is not typically restrictive in agricultural zones. THOWs have legal ambiguity with minimal enforcement in rural areas. Water and septic are critical considerations—towns have municipal systems, but unincorporated properties require wells (feasible but expensive for deep aquifer drilling common in central Washington) or water rights, plus septic approval. The flat to gently rolling Columbia Basin terrain experiences hot, dry summers and cold winters. Before purchasing land in Adams County, thoroughly verify water availability through well drilling feasibility or existing water rights, confirm septic approval through Adams County Health District, check agricultural zoning compatibility, and understand minimal county enforcement creates flexibility but requires owner responsibility for proper construction and infrastructure.

Asotin County, Washington's southeastern corner along the Snake River and Idaho border, combines Lewiston metropolitan influence with rugged canyon terrain. The county administers zoning in unincorporated areas, while Asotin and Clarkston run their own codes. In county areas, tiny houses on foundations must meet health district septic requirements. Minimum square footage varies by zone. THOWs classified as RVs with restrictions. Water and septic vary—Clarkston has municipal systems, but rural canyon areas require wells (challenging and expensive in basalt canyon geology with variable success) and septic approval (difficult on steep slopes). The dramatic Snake River canyon creates infrastructure challenges. Before purchasing land in Asotin County, thoroughly investigate well drilling feasibility and costs in basalt terrain, verify septic approval on steep canyon slopes through Asotin County Health District, personally inspect access on winding canyon roads, determine jurisdiction between county and cities, and recognize canyon terrain creates infrastructure challenges that often exceed regulatory concerns in this relatively low-regulation eastern Washington county.

Benton County, in southeastern Washington's Tri-Cities region, combines urban development around Kennewick and Richland with agricultural areas. The county distinguishes between incorporated cities (Kennewick, Richland, West Richland, Prosser, and Benton City, each with own codes and some ADU provisions) and unincorporated areas. In cities with ADU ordinances, foundation-built tiny houses may qualify as ADUs subject to size limits, setbacks, design standards, and parking requirements. In county areas, regulations focus on agricultural zoning and septic approval. THOWs classified as RVs with restrictions. Water and sewer vary—cities have municipal systems including Tri-Cities shared infrastructure, unincorporated areas may require wells (feasible but expensive in Columbia Basin) or irrigation district connections, plus septic. Hanford Site nuclear legacy affects portions of the county. Before purchasing land in Benton County, determine jurisdiction between cities and county, review applicable ADU ordinances in Tri-Cities if relevant, verify water source including irrigation district availability, confirm septic approval through Benton-Franklin Health District, check for Hanford-related restrictions if near the site, and understand Tri-Cities metro growth brings more comprehensive planning than typical eastern Washington counties.

Chelan County, in North Central Washington along Lake Chelan and the Columbia River, combines tourism development, fruit orchards, and mountain recreation with varied terrain challenges. The county distinguishes between Wenatchee, Chelan, Leavenworth, Entiat, and Cashmere (each with own codes driven by tourism or orchard economics) and unincorporated areas. In county areas, tiny houses on foundations must meet health district septic requirements and county zoning. Some zones have minimum square footages, particularly near tourism areas. THOWs classified as RVs with restrictions especially in tourist zones. Water and septic vary—cities have municipal systems, orchard areas often have irrigation district connections, mountain/rural areas require wells (variable success in mountain geology) and septic (challenging on slopes). Lake Chelan and Cascade foothills create diverse conditions. Before purchasing land in Chelan County, determine jurisdiction and applicable zoning overlay districts, verify water through municipal, irrigation district, or well feasibility, confirm septic approval through Chelan-Douglas Health District with attention to slope limitations, check for shoreline management restrictions near Lake Chelan or Columbia River, and understand tourism and orchard economies create higher land costs and more development scrutiny than typical eastern Washington counties.

Clallam County, on Washington's Olympic Peninsula north coast, combines Port Angeles urban development, Olympic National Park tourism, and rural communities with significant rainfall and terrain challenges. The county distinguishes between Port Angeles, Sequim (in the rain shadow), Forks, and unincorporated areas. In county areas, tiny houses on foundations must meet health district septic requirements and county zoning influenced by Growth Management Act. Some zones have minimum square footages. THOWs classified as RVs. Water and septic vary—Port Angeles has municipal, rural areas require wells (abundant but shallow in coastal areas, requiring maintenance) and septic (challenging in high rainfall/poor drainage soils). Sequim's rain shadow creates drier conditions. Olympic National Park proximity brings environmental regulations. Before purchasing land in Clallam County, determine jurisdiction and Growth Management Act designations, verify water through wells understanding coastal water table issues or municipal connections, confirm septic approval through Clallam County Health Department with attention to drainage in high rainfall zones (less concern in Sequim rain shadow), check for shoreline, critical areas, or park adjacency restrictions, and recognize Olympic Peninsula's isolation, high rainfall outside rain shadow, and tourism economy create unique challenges and higher development costs.

Clark County, in southwest Washington as part of the Portland metropolitan area, has adopted comprehensive ADU regulations reflecting urban growth pressures. The county contains Vancouver, Camas, Washougal, Ridgefield, La Center, Battle Ground, and Yacolt (each with own codes and ADU provisions). Vancouver and other cities allow ADUs subject to size limits, setbacks, design standards, parking, and often owner-occupancy requirements. Foundation-built tiny houses can qualify as ADUs. In unincorporated county areas, Growth Management Act influences development with urban growth boundaries and designated rural areas. THOWs prohibited for permanent occupancy outside designated RV parks. Water and sewer vary—cities have municipal systems, rural areas require wells (feasible in foothills with good water table) and septic. Portland metropolitan influence drives higher land costs and comprehensive planning. Before purchasing land in Clark County, determine jurisdiction and Growth Management Act designation (urban, rural, resource), review applicable ADU ordinances in Vancouver or other cities, verify water and sewer or well/septic feasibility, check for critical areas or environmental restrictions, understand Portland metro integration brings sophisticated regulation and expensive land, and prepare for comprehensive permit review processes in this Washington county most influenced by Oregon metro growth.

Columbia County, in southeastern Washington's Blue Mountains foothills, offers agricultural character, small-town living, and minimal regulatory oversight. The county administers basic zoning, while Dayton and Starbuck run limited codes. In county areas, tiny houses on foundations can proceed if meeting health district septic requirements. Minimum square footage not typically restrictive. THOWs have legal ambiguity with minimal enforcement in rural areas. Water and septic critical—towns have limited municipal service, most properties require wells (feasible but may be deep and expensive in foothill areas) and septic approval. Rolling hills transitioning to Blue Mountains create scenic but infrastructure-challenging terrain. Before purchasing land in Columbia County, verify water through well drilling feasibility assessment understanding foothill aquifer depth, confirm septic approval through Columbia County Health District, check agricultural zoning, personally inspect access especially in foothill areas, and understand minimal enforcement creates flexibility with owner responsibility for proper construction in this quiet, rural southeastern Washington county with traditional agricultural economy.

Cowlitz County, in southwest Washington along the Columbia River between Portland and Olympia, combines industrial heritage (Longview timber history) with I-5 corridor growth. The county distinguishes between Longview, Kelso, Castle Rock, Kalama, Woodland, and unincorporated areas. Longview and Kelso have adopted ADU regulations where foundation-built tiny houses may qualify subject to standards. In county areas, Growth Management Act influences development patterns. THOWs classified as RVs with restrictions. Water and sewer vary—cities have municipal systems, rural areas require wells (feasible in Cowlitz lowlands with good water table) and septic. Columbia River creates lowland terrain with some flood concerns. Mount St. Helens proximity. Before purchasing land in Cowlitz County, determine jurisdiction and review ADU provisions in Longview/Kelso if applicable, verify water/sewer or well/septic feasibility, check flood zones near Columbia or Cowlitz rivers, confirm septic approval through Cowlitz County Health Department, understand Growth Management Act affects rural development, and recognize I-5 corridor location creates more development pressure and regulation than isolated rural counties while still less expensive than Seattle/Tacoma metro.

Douglas County, in Central Washington along the Columbia River centered on Waterville and East Wenatchee, combines orchard agriculture with Columbia River recreation. The county administers zoning, while East Wenatchee, Rock Island, Bridgeport, and Mansfield run own codes. In county areas, tiny houses on foundations must meet health district septic and county zoning. Some zones have minimums. THOWs classified as RVs. Water and septic vary—East Wenatchee has municipal, orchard areas often have irrigation district connections, plateau areas require wells (expensive and deep in basalt) and septic. Columbia Plateau terrain. Before purchasing, determine jurisdiction, verify water through municipal, irrigation, or well feasibility, confirm septic through Chelan-Douglas Health District, check for shoreline restrictions near Columbia River, and understand orchard economy creates moderate land costs with seasonal employment character.

Ferry County, in northeastern Washington along the Canadian border, offers remote mountain terrain, forestland, and minimal oversight but significant infrastructure challenges. The county administers basic zoning, while Republic runs limited code. In county areas, tiny houses on foundations can proceed if meeting septic, though mountain terrain creates challenges. Minimum square footage not restrictive. THOWs have legal ambiguity with minimal enforcement. Water and septic major challenges—Republic has limited municipal, most areas require wells (expensive through mountain geology with variable success) and septic (difficult on slopes/shallow soils). Remote location with harsh winters. Colville National Forest. Before purchasing, thoroughly investigate well feasibility and costs, verify septic on mountain terrain through Ferry County Health Department, personally inspect access and winter maintenance, understand extreme remoteness and isolation, and recognize infrastructure challenges and distance from services often exceed regulatory concerns in this sparsely populated mountain county.

Franklin County, in southeastern Washington's Tri-Cities region centered on Pasco, combines urban growth with agricultural areas. The county distinguishes between Pasco, Connell, Kahlotus, and Mesa and unincorporated areas. In Pasco, some ADU provisions may exist—verification needed. In county areas, regulations focus on agricultural zoning and septic. THOWs classified as RVs. Water and sewer vary—Pasco has municipal, unincorporated areas require wells or irrigation district connections plus septic. Columbia Basin terrain. Hanford Site proximity. Before purchasing, determine jurisdiction, review Pasco regulations, verify water source, confirm septic through Benton-Franklin Health District, and understand Tri-Cities growth brings more regulation than rural eastern Washington.

Garfield County, Washington's least populated county in the southeast, offers agricultural plains, Palouse wheat country character, and minimal oversight. The county administers basic zoning, while Pomeroy runs limited code. In county areas, tiny houses on foundations proceed if meeting septic. Minimum square footage not restrictive. THOWs have legal ambiguity with minimal enforcement. Water and septic vary—Pomeroy has municipal, rural requires wells (feasible in Palouse) and septic. Rolling Palouse hills. Before purchasing, verify water feasibility, confirm septic through Garfield County Health District, check agricultural zoning, and understand minimal enforcement creates flexibility with owner responsibility in this quiet farming community.

Grant County, in central Washington's Columbia Basin, combines large-scale irrigated agriculture, Moses Lake regional center, and minimal regulatory oversight. The county administers zoning, while Moses Lake, Ephrata, Quincy, Soap Lake, Warden, Wilson Creek, Coulee City, Electric City, Grand Coulee, Krupp, Mattawa, and Royal City run own codes. In county areas, tiny houses on foundations must meet health district septic and agricultural zoning. Minimum square footage varies. THOWs classified as RVs. Water critical—cities have municipal, unincorporated areas require wells (expensive and deep in Columbia Basin basalt) or Columbia Basin Irrigation District connections, plus septic. Flat to rolling plateau terrain. Before purchasing, thoroughly verify water availability through irrigation district or well feasibility/costs, confirm septic through Grant County Health District, check agricultural zoning compatibility, and understand Moses Lake regional services provide more infrastructure than typical rural central Washington but county remains relatively low-regulation with water as primary development constraint.

Grays Harbor County, on Washington's southwest coast centered on Aberdeen and Hoquiam, combines timber industry heritage, coastal communities, and high-rainfall challenges. The county distinguishes between Aberdeen, Hoquiam, Cosmopolis, Montesano, Ocean Shores, Westport, and others and unincorporated areas. In county areas, tiny houses on foundations must meet health district septic and county zoning. Some zones have minimums. THOWs classified as RVs. Water and septic challenges—cities have municipal, rural coastal areas require wells (shallow water table but maintenance issues in wet climate) and septic (very challenging in high rainfall, poor drainage soils, and high water table). Heavy rainfall averaging 80+ inches annually creates infrastructure challenges. Before purchasing, verify water through wells understanding coastal conditions or municipal connections, confirm septic approval through Grays Harbor County Public Health with particular attention to drainage and water table (septic often most limiting factor), check for shoreline or flood restrictions, and recognize high rainfall, timber economy transition, and coastal exposure create unique challenges in this economically challenged region.

Island County, comprising Whidbey and Camano islands in Puget Sound, combines scenic beauty, Naval Air Station Whidbey Island, tourism, and Growth Management Act planning. The county distinguishes between Oak Harbor, Coupeville, Langley, and unincorporated areas. Cities have adopted ADU regulations where foundation-built tiny houses may qualify subject to standards. In county areas, Growth Management Act strongly influences development with designated rural areas, shoreline management, and critical areas protections. THOWs classified as RVs. Water and sewer vary—cities have municipal, rural areas require wells (generally feasible on islands with shallow water table but quality varies) and septic (challenging with high water table, marine proximity, and aquifer protection concerns). Ferry-dependent access. Before purchasing, determine jurisdiction and review ADU provisions in cities, verify water/septic with particular attention to Island County Health Department septic requirements (often restrictive to protect aquifer), check Growth Management Act designations and shoreline restrictions, understand ferry dependence affects lifestyle and costs, and recognize island living creates higher costs but scenic appeal with moderate regulatory environment allowing ADUs in cities while protecting rural character.

Jefferson County, on the Olympic Peninsula's eastern side, combines Port Townsend Victorian charm, Olympic National Park/Forest access, and Growth Management Act planning. The county distinguishes between Port Townsend and unincorporated areas. In county areas, Growth Management Act and shoreline management create complex regulations. Tiny houses on foundations must meet health district septic and county codes. Some zones have minimums. THOWs classified as RVs. Water and septic vary—Port Townsend has municipal, rural areas require wells (feasible but shallow in coastal areas) and septic (challenging in wet soils, high water table). Rain shadow effect creates variable rainfall. Before purchasing, determine jurisdiction and Growth Management Act designation, verify water/septic with attention to Jefferson County Public Health requirements, check shoreline and critical areas restrictions, understand ferry or Hood Canal Bridge access creates isolation, and recognize environmental protections and scenic preservation create higher regulation and costs than typical rural counties.

King County, Washington's most populous county centered on Seattle, has adopted comprehensive ADU regulations driven by housing affordability crisis and state legislation. The county contains Seattle, Bellevue, Renton, Kent, Auburn, Federal Way, and many other cities (each with own codes and ADU provisions). Seattle allows ADUs with streamlined approval, no owner-occupancy requirement since 2019, and liberal standards. Other cities vary but most allow ADUs. Foundation-built tiny houses can qualify as ADUs meeting local standards. In unincorporated King County areas (rural east county), Growth Management Act designates urban and rural areas with different rules. THOWs prohibited for permanent occupancy outside RV parks. Water and sewer vary—cities have municipal systems, rural areas require wells/septic with challenging approval. Before purchasing, determine jurisdiction and review specific city ADU ordinances, verify water/sewer or wells/septic feasibility, check Growth Management Act designation, understand Seattle metro means expensive land and comprehensive regulation but also most progressive ADU/tiny house acceptance, and recognize King County represents Washington's most sophisticated and expensive housing market but also offers most regulatory pathways for foundation-built tiny houses as ADUs.

Kitsap County, on the Kitsap Peninsula across Puget Sound from Seattle, combines Naval Base Kitsap, commuter communities, and Growth Management Act planning. The county contains Bremerton, Port Orchard, Bainbridge Island, Poulsbo, and unincorporated areas. Cities have adopted ADU regulations where foundation-built tiny houses may qualify. In county areas, Growth Management Act influences development. THOWs classified as RVs. Water and sewer vary—cities have municipal, rural areas require wells (feasible with shallow peninsula water table) and septic (challenging with high water table and marine proximity). Ferry-dependent for Seattle access. Naval base dominance. Before purchasing, determine jurisdiction and review ADU provisions, verify water/septic with Kitsap Public Health District (septic can be challenging), check Growth Management Act designations, understand ferry commute lifestyle, and recognize Kitsap combines Seattle metro affordability with island living creating moderate regulation with ADU opportunities in cities.

Kittitas County, in central Washington centered on Ellensburg with I-90 corridor access, combines university town (Central Washington University), ranching, and Cascade foothills recreation. The county distinguishes between Ellensburg, Cle Elum, Roslyn, South Cle Elum, and Kittitas and unincorporated areas. In county areas, tiny houses on foundations must meet health district septic and county zoning. Some zones have minimums especially near Ellensburg or I-90. THOWs classified as RVs. Water and septic vary—Ellensburg has municipal, rural areas require wells (feasible in valley, challenging in foothills) and septic. Yakima River valley terrain. Before purchasing, determine jurisdiction, verify water through wells or municipal, confirm septic through Kittitas County Public Health, check zoning especially in growth areas, and understand university and I-90 location create moderate development pressure with more oversight than isolated rural counties but less expensive than Puget Sound.

Klickitat County, in south-central Washington along the Columbia River Gorge, combines scenic beauty, wind energy development, and minimal oversight. The county administers zoning, while Goldendale, White Salmon, Bingen, and Lyle run own codes. In county areas, tiny houses on foundations must meet health district septic. Minimum square footage not typically restrictive. THOWs have legal ambiguity with minimal enforcement in rural areas. Water and septic vary—towns have limited municipal, most require wells (variable success in Columbia Gorge geology) and septic. Dramatic terrain from Gorge to plateau. Before purchasing, verify water through well feasibility, confirm septic through Klickitat County Public Health, check for Columbia Gorge National Scenic Area restrictions if applicable, personally inspect access, and understand scenic beauty with minimal regulation creates opportunities with infrastructure responsibility in this rural, economically modest county.

Lewis County, in southwest Washington centered on Chehalis and Centralia along I-5, combines timber heritage, I-5 corridor location, and traditional rural character. The county distinguishes between Chehalis, Centralia, Morton, Mossyrock, Napavine, Pe Ell, Toledo, Vader, and Winlock and unincorporated areas. In county areas, tiny houses on foundations must meet health district septic and county zoning. Some zones have minimums. THOWs classified as RVs. Water and sewer vary—cities have municipal, rural areas require wells (feasible with good water table in lowlands) and septic. Western Washington rainfall creates wet conditions. Before purchasing, determine jurisdiction, verify water/septic, confirm septic approval through Lewis County Public Health, check zoning, and understand I-5 location creates more activity than isolated counties while timber economy transition and rural character maintain moderate costs and less regulation than Puget Sound metro.

Lincoln County, in eastern Washington's wheat country centered on Davenport, offers Palouse agricultural character and minimal oversight. The county administers basic zoning, while Davenport, Sprague, Reardan, Odessa, Harrington, Wilbur, and Creston run limited codes. In county areas, tiny houses on foundations proceed if meeting septic. Minimum square footage not restrictive. THOWs have legal ambiguity with minimal enforcement. Water and septic vary—towns have municipal, rural requires wells (feasible in Palouse with aquifer access) and septic. Rolling wheat country. Before purchasing, verify water feasibility, confirm septic through Lincoln County Health Department, check agricultural zoning, and understand minimal enforcement creates flexibility with owner responsibility in this quiet farming region.

Mason County, on southern Puget Sound centered on Shelton, combines timber heritage, Hood Canal recreation, and rural character with some growth pressure. The county distinguishes between Shelton and unincorporated areas. In county areas, Growth Management Act influences development. Tiny houses on foundations must meet health district septic and county zoning. Some zones have minimums. THOWs classified as RVs. Water and septic vary—Shelton has municipal, rural areas require wells (feasible but shallow with maintenance concerns) and septic (challenging with high water table, wet soils, and shoreline proximity). Hood Canal creates marine environment. Before purchasing, verify water/septic, confirm septic approval through Mason County Public Health (often challenging), check Growth Management Act designations and shoreline restrictions, and understand proximity to Olympia creates moderate growth pressure with environmental protections while timber economy maintains rural character and moderate costs.

Okanogan County, Washington's largest county in the north-central region, combines vast wilderness, ranching, Okanogan-Wenatchee National Forest, and minimal oversight with infrastructure challenges. The county administers zoning, while Omak, Okanogan, Tonasket, Oroville, Brewster, Conconully, Coulee Dam, Elmer City, Nespelem, Pateros, Riverside, Twisp, and Winthrop run own codes. In county areas, tiny houses on foundations must meet health district septic. Minimum square footage not typically restrictive. THOWs have legal ambiguity with minimal enforcement in remote areas. Water and septic vary—towns have limited municipal, most require wells (expensive with deep drilling in mountain/plateau terrain) and septic. Dramatic terrain from Cascade mountains to Okanogan highlands. Canadian border. Before purchasing, thoroughly investigate well feasibility and costs, verify septic through Okanogan County Public Health, personally inspect access and winter conditions, understand extreme remoteness and harsh winters, and recognize infrastructure challenges and distance from services create primary development constraints in this vast, sparsely populated county with minimal regulation but significant practical challenges.

Pacific County, on Washington's southwest coast, offers ocean beaches, Willapa Bay oyster heritage, and high-rainfall challenges. The county distinguishes between South Bend, Raymond, Long Beach, Ilwaco, and unincorporated coastal areas. In county areas, tiny houses on foundations must meet health district septic and county zoning. Some zones have minimums. THOWs classified as RVs. Water and septic major challenges—towns have municipal, coastal areas require wells (shallow water table with saltwater intrusion concerns) and septic (very difficult in high rainfall, poor drainage, and high water table). Extreme rainfall and coastal exposure. Before purchasing, verify water/septic, confirm septic approval through Pacific County Health Department (septic often impossible on poor sites), check for shoreline and flood restrictions, and recognize coastal isolation, high rainfall, and economic challenges create unique environment with septic approval often determining development feasibility more than regulations.

Pend Oreille County, in Washington's remote northeastern corner bordering Idaho, offers forested mountain terrain, Pend Oreille River recreation, and minimal oversight with significant infrastructure challenges. The county administers basic zoning, while Newport, Cusick, Ione, Metaline, and Metaline Falls run limited codes. In county areas, tiny houses on foundations can proceed if meeting septic, though mountain terrain creates challenges. Minimum square footage not restrictive. THOWs have legal ambiguity with minimal enforcement. Water and septic major challenges—towns have limited municipal, most require wells (expensive through mountain geology with variable success) and septic (difficult on slopes). Extreme remoteness and harsh winters. Colville National Forest dominates. Before purchasing, thoroughly investigate well costs, verify septic through Pend Oreille County Health Department on mountain terrain, personally inspect access and winter maintenance, understand extreme isolation and limited services, and recognize infrastructure and access challenges exceed regulatory concerns in this remote mountain county.

Pierce County, Washington's second-most populous county centered on Tacoma, has adopted ADU regulations reflecting Seattle metro growth and housing pressures. The county contains Tacoma, Lakewood, Puyallup, University Place, Bonney Lake, Auburn (shared), Federal Way (shared), and many other cities (each with own codes and ADU provisions). Tacoma and most cities allow ADUs subject to standards. Foundation-built tiny houses can qualify as ADUs. In unincorporated county areas, Growth Management Act designates urban and rural areas. THOWs prohibited for permanent occupancy outside RV parks. Water and sewer vary—cities have municipal, rural areas require wells/septic. Mount Rainier proximity. Joint Base Lewis-McChord. Before purchasing, determine jurisdiction and review ADU ordinances, verify water/sewer or wells/septic, check Growth Management Act designation, understand Tacoma metro means comprehensive regulation but ADU pathways exist, and recognize Pierce County offers more affordable alternative to Seattle/King County while maintaining similar progressive housing policies and ADU opportunities.

San Juan County, comprising the San Juan Islands in northern Puget Sound, combines stunning natural beauty, tourism economy, environmental protections, and ferry-dependent isolation creating complex regulations. The county contains Friday Harbor and unincorporated islands. Growth Management Act, shoreline management, and critical areas protections create restrictive development environment. Tiny houses on foundations must meet very challenging health district septic requirements and county codes. Minimum square footages exist in zones. THOWs face restrictions. Water and septic major challenges—Friday Harbor has municipal, island properties require wells (feasible but limited capacity) and septic (extremely difficult with rocky shallow soils, high water table, marine aquifer protection). Ferry-dependent access. Expensive land. Before purchasing, verify water/septic (septic approval often impossible on marginal sites), confirm San Juan County Health Department requirements, check Growth Management Act and shoreline restrictions, understand ferry dependence and isolation, and recognize San Juan Islands represent Washington's most expensive and environmentally protected county where tiny house placement faces extreme challenges from cost, septic limitations, and preservation-oriented regulations.

Skagit County, in northwest Washington between Puget Sound and the Cascades, combines Mount Vernon and Burlington urban centers, agricultural Skagit Valley, and Growth Management Act planning. The county contains Mount Vernon, Burlington, Anacortes, Sedro-Woolley, and others. Cities have adopted ADU regulations. In county areas, Growth Management Act influences development with agricultural preservation and urban growth boundaries. THOWs classified as RVs. Water and sewer vary—cities have municipal, rural areas require wells (feasible in valley) and septic (challenging in wet soils). Agricultural economy. Before purchasing, determine jurisdiction and review ADU provisions, verify water/septic, check Growth Management Act designations especially agricultural preservation, and understand Skagit combines Seattle metro accessibility with agricultural character creating moderate regulation with ADU opportunities in cities while protecting farmland.

Skamania County, in the Columbia River Gorge centered on Stevenson, combines dramatic scenery, Gifford Pinchot National Forest, Columbia River Gorge National Scenic Area, and minimal oversight with terrain challenges. The county administers zoning, while Stevenson and North Bonneville run own codes. In county areas, tiny houses on foundations must meet health district septic. Minimum square footage not typically restrictive. THOWs have legal ambiguity. Water and septic vary—towns have limited municipal, most require wells (variable success in Gorge geology) and septic (challenging on slopes). Columbia River Gorge National Scenic Area creates additional federal restrictions in portions. Before purchasing, verify water through well feasibility, confirm septic through Skamania County Community Health on steep terrain, check for Gorge National Scenic Area restrictions, personally inspect access, and understand scenic beauty with minimal county regulation creates opportunities but terrain and federal Gorge protections create challenges.

Snohomish County, north of Seattle in the Puget Sound metro, has adopted ADU regulations reflecting growth pressures and state legislation. The county contains Everett, Lynnwood, Marysville, Edmonds, Mountlake Terrace, Mukilteo, Mill Creek, Lake Stevens, Arlington, Snohomish, Monroe, Sultan, and others. Most cities allow ADUs subject to standards. Foundation-built tiny houses can qualify as ADUs. In county areas, Growth Management Act designates urban and rural areas. THOWs prohibited for permanent occupancy outside RV parks. Water and sewer vary—cities have municipal, rural areas require wells/septic. Seattle metro growth. Boeing presence. Before purchasing, determine jurisdiction and review ADU ordinances, verify water/sewer or wells/septic, check Growth Management Act designation, and understand Snohomish County combines Seattle metro accessibility with more affordable housing than King County while maintaining similar progressive ADU policies creating opportunities for foundation-built tiny houses in cities.

Spokane County, in eastern Washington centered on Spokane city, combines Washington's second-largest city with surrounding suburban and rural areas. The county contains Spokane, Spokane Valley, Cheney, Medical Lake, Airway Heights, Deer Park, Liberty Lake, Millwood, and others. Spokane city has adopted ADU regulations where foundation-built tiny houses may qualify subject to standards. Other cities vary. In county areas, regulations focus on zoning and septic. THOWs classified as RVs. Water and sewer vary—cities have municipal including shared Spokane Aquifer use, rural areas require wells (feasible from Spokane Aquifer) and septic. Rolling Palouse to forested foothills terrain. Before purchasing, determine jurisdiction and review Spokane ADU provisions or other city codes, verify water source including aquifer sustainability, confirm septic through Spokane Regional Health District, check county zoning, and understand Spokane represents eastern Washington's largest metro with most regulatory sophistication including ADU pathways while remaining more affordable than western Washington.

Stevens County, in northeastern Washington centered on Colville, combines forested mountain terrain, Colville National Forest, and minimal oversight with infrastructure challenges. The county administers zoning, while Colville, Chewelah, Kettle Falls, Springdale, Loon Lake, Marcus, Northport, and others run own codes. In county areas, tiny houses on foundations must meet health district septic. Minimum square footage not typically restrictive. THOWs have legal ambiguity with minimal enforcement in rural areas. Water and septic vary—towns have municipal, rural mountain areas require wells (expensive through mountain geology) and septic (challenging on slopes). Mountain terrain. Harsh winters. Before purchasing, thoroughly investigate well feasibility and costs, verify septic through Stevens County Health Department on terrain, personally inspect access and winter conditions, understand remoteness, and recognize infrastructure challenges often exceed regulatory concerns in this mountain county with traditional rural character.

Thurston County, centered on Olympia (Washington's capital), combines state government employment, regional commerce, and Growth Management Act planning. The county contains Olympia, Lacey, Tumwater, Yelm, Tenino, Rainier, and Bucoda. Olympia and other cities have adopted ADU regulations where foundation-built tiny houses may qualify. In county areas, Growth Management Act influences development. THOWs classified as RVs. Water and sewer vary—cities have municipal, rural areas require wells (feasible in lowlands) and septic. Western Washington rainfall. Before purchasing, determine jurisdiction and review ADU ordinances in Olympia or other cities, verify water/sewer or wells/septic, check Growth Management Act designations, confirm septic through Thurston County Environmental Health if needed, and understand state capital location creates more sophisticated regulation with comprehensive planning while ADU adoption provides pathways for foundation-built tiny houses in cities.

Wahkiakum County, Washington's smallest county on the lower Columbia River, offers rural fishing/timber character and minimal oversight. The county administers basic zoning, while Cathlamet runs limited code. In county areas, tiny houses on foundations can proceed if meeting septic. Minimum square footage not restrictive. THOWs have legal ambiguity with minimal enforcement. Water and septic vary—Cathlamet has municipal, rural requires wells (feasible in Columbia lowlands) and septic. Western Washington rainfall. Columbia River creates lowland terrain. Before purchasing, verify water feasibility, confirm septic through Wahkiakum County Health and Human Services, check zoning, and understand minimal enforcement creates flexibility with owner responsibility in this quiet, isolated river county.

Walla Walla County, in southeastern Washington bordering Oregon, combines wine country, agricultural heritage, and the regional center of Walla Walla city. The county distinguishes between Walla Walla, College Place, Prescott, Waitsburg, and unincorporated areas. Walla Walla city has adopted ADU regulations where foundation-built tiny houses may qualify subject to standards. In county areas, regulations focus on agricultural zoning and septic. THOWs classified as RVs. Water and sewer vary—cities have municipal, rural areas require wells (feasible in valley, may be deep) or irrigation district connections, plus septic. Rolling hills transitioning to Blue Mountains. Wine tourism. Before purchasing, determine jurisdiction and review Walla Walla ADU provisions if applicable, verify water through municipal, irrigation, or well feasibility, confirm septic through Walla Walla County Health Department, check agricultural zoning, and understand wine country creates moderate land costs with Walla Walla city providing regional services and progressive ADU regulations while rural county remains traditional agricultural character.

Whatcom County, in northwest Washington on the Canadian border, combines Bellingham regional center, Western Washington University, agricultural Nooksack Valley, and North Cascades mountain access. The county contains Bellingham, Ferndale, Lynden, Blaine, Everson, Nooksack, and Sumas. Bellingham and other cities have adopted ADU regulations. Foundation-built tiny houses can qualify as ADUs. In county areas, Growth Management Act influences development with agricultural and forest preservation. THOWs classified as RVs. Water and sewer vary—cities have municipal, rural areas require wells (feasible in lowlands, challenging in mountains) and septic (challenging in wet conditions). Canadian border. Mount Baker recreation. Before purchasing, determine jurisdiction and review ADU provisions, verify water/septic, check Growth Management Act designations, confirm septic through Whatcom County Health Department, and understand Bellingham provides progressive college town atmosphere with ADU opportunities while county protects agriculture and environment creating balanced approach to development.

Whitman County, in southeastern Washington's Palouse wheat country, combines Washington State University in Pullman with agricultural heritage. The county distinguishes between Pullman, Colfax, Palouse, Tekoa, Rosalia, Oakesdale, Uniontown, Colton, Farmington, Garfield, Albion, Malden, St. John, Endicott, and LaCrosse and unincorporated areas. Pullman has adopted ADU regulations driven by university housing needs. Foundation-built tiny houses may qualify as ADUs. In county areas, regulations focus on agricultural zoning and septic. THOWs classified as RVs. Water and sewer vary—Pullman and Colfax have municipal, rural requires wells (feasible in Palouse aquifer) and septic. Rolling Palouse hills create dramatic terrain. Before purchasing, determine jurisdiction and review Pullman ADU provisions if applicable, verify water through wells or municipal, confirm septic through Whitman County Public Health, check agricultural zoning, and understand university presence creates housing innovation in Pullman while rural Palouse maintains traditional agricultural character with minimal oversight.

Yakima County, in south-central Washington centered on Yakima city, combines extensive fruit orchards, wine country, and Hispanic cultural influence. The county contains Yakima, Union Gap, Selah, Sunnyside, Grandview, Toppenish, Wapato, Zillah, Tieton, Naches, and others. Yakima city may have ADU provisions—verification needed. In county areas, regulations focus on agricultural zoning and septic. THOWs classified as RVs. Water critical—cities have municipal, orchard areas have irrigation district connections, rural areas require wells (expensive and deep in Yakima Valley with water rights complexity) or irrigation rights, plus septic. Yakima Valley orchards dominate economy. Before purchasing, determine jurisdiction and review Yakima regulations, thoroughly verify water availability through irrigation district or well feasibility (water most limiting factor), confirm septic through Yakima Health District, check agricultural zoning, and understand orchard economy creates seasonal employment character with water availability determining development feasibility more than regulations in this agricultural powerhouse county.