The Growth Management Act (GMA) requires that certain counties, and the cities within those counties, engage in planning for future population growth.  Currently, 18 counties are required to plan, 10 have chosen to plan, and 11 are not subject to the full GMA planning requirements.  
The central part of the planning process is the comprehensive plan, which is a generalized, coordinated land use policy statement.  The Legislature has established 14 goals that should act as the basis for all comprehensive plans.  Examples of goals include reducing sprawl, providing for affordable housing, and protecting property rights.  The comprehensive plan addresses these goals, and sets out the policies and standards that are meant to guide the city or county's actions and decisions in the future.  These plans are required to be updated every eight years and must contain certain elements, such as a transportation element, a rural development element, and a capital facilities plan.  These elements must satisfy the requirements for each element while fitting within the overall comprehensive plan.

One element required in the comprehensive plan is the land use element.  This requires the designation of the proposed general distribution, location, and uses of land. It must include population densities, building intensities, and estimates of future growth.  The land use element is required to provide for the protection of the quality and quantity of groundwater used for public water supplies.  When possible, the land use element should consider planning approaches that promote physical activity.  In counties and cities in which it is applicable, the land use element must also review drainage, stormwater, and flooding, and provide guidance on taking corrective actions to mitigate or cleanse these discharges that pollute the waters of the state.

Another element of a comprehensive plan is the housing element.  This element is meant to ensure the vitality and character of established neighborhoods.  It must include the identification of the number of housing units required based on existing and projected growth.  The housing element must include a statement of goals and policies for the preservation, improvement, and development of housing, including single-family housing.  It is also required to make provisions for the existing and future needs of all economic segments of the population, and to identify sufficient land for housing, including government assisted or low-income housing, manufactured housing, and multifamily or group home housing.

Counties, together with cities within the county, are required to develop a countywide planning policy to provide a framework in which the county and the cities can develop consistent comprehensive plans.  Within 14 months of a county initially becoming subject to the GMA's requirements, the county must adopt a countywide planning policy in consultation with the cities within the county.  The policy must address urban growth areas (UGAs); policies to promote orderly development; policies for siting state or countywide capital facilities; policies and strategies for countywide transportation; policies considering the need for affordable housing; policies for countywide economic development; and the fiscal impact of these policies.  Failure to adopt a countywide planning policy can subject the county and cities therein to sanctions from the Governor, including the withholding of certain tax revenue.  Countywide planning policies may be appealed by cities or the Governor to the Growth Management Hearings Board for 60 days after their adoption.

The housing element of the comprehensive plan must include provisions for the preservation, improvement, and development of housing, including, in UGAs, single-family residences such as detached dwellings, duplexes, triplexes, and townhomes.  The housing element must also identify sufficient land for housing, including, in a UGA, single-family residences such as detached dwellings, duplexes, triplexes, and townhomes.  The housing element is required to make adequate provisions for all economic needs of the community, including the consideration of housing in relation to employment locations.

The housing element must link the housing goals of the planning jurisdiction to those of the overall county goals to ensure that the goals of the housing element are met.  If a county or city does not include all housing types in its plans, including, in a UGA, single-family residences such as detached dwellings, duplexes, triplexes, and townhomes, then the countywide planning policies must explain how the county and its cities will, as a whole meet all the existing and projected housing needs of all economic segments of the community during the planning period.

Countywide planning policies must be updated at least 14 months prior to the deadline for the county to revise its comprehensive plan.  These policies must include policies that consider the need for affordable housing, and address how the county and cities will meet the requirements to consider all required housing types, including, in a UGA, single-family residences such as detached dwellings, duplexes, triplexes, and townhomes.  The policies must specify how the county and cities will ensure the housing element requirements are met as the county and cities update their comprehensive plans.  The countywide planning policies must also address how the county and cities will jointly satisfy the requirements of the land use element. 

Counties and cities outside of Clark, King, Kitsap, Pierce, Snohomish, Thurston, and Whatcom counties are not required to comply with requirements related to consideration of and planning for duplexes, triplexes, and townhomes within a UGA if the city or county adopts findings and provides evidence that either the current infrastructure within the UGA will not support such development, or that it is unlikely that such infrastructure will be built to support such development within the 20-year planning period.