Key Housing Concepts#

Greenfield vs. Brownfield#

Greenfield development refers to building on previously undeveloped land, typically agricultural or forest land located on the urban fringe. Because Oregon’s land use laws prioritize the preservation of farm and forest lands, greenfield development is strictly regulated and generally occurs only when a city expands its Urban Growth Boundary (UGB) to accommodate demonstrated housing needs. While greenfield sites offer a “clean slate” for developers, they often require significant new infrastructure investments (roads, sewers, utilities) and are the primary subject of debates regarding urban sprawl versus housing supply.

Brownfield development, conversely, involves the redevelopment of previously used industrial or commercial sites that may be complicated by environmental contamination. Oregon actively encourages brownfield redevelopment—such as transforming old gas stations, mills, or rail yards into housing—as a strategy to revitalize neighborhoods and reduce pressure on greenfield expansion. Projects like “The Yards” in Portland demonstrate how these sites can be remediated to provide essential affordable housing close to existing services and transit, though they often face higher upfront costs and regulatory complexities related to cleanup.

Naturally Affordable Housing#

Naturally affordable housing (also called “naturally occurring affordable housing” or NOAH) refers to housing units that are affordable to low- and moderate-income households without government subsidies or income restrictions. These units become affordable through market forces—typically because they are older, smaller, in less desirable locations, or have fewer amenities than newer construction. In contrast to subsidized affordable housing (such as Section 8 or Low-Income Housing Tax Credit developments), naturally affordable housing has no deed restrictions, meaning landlords can raise rents to market rate at any time.

Naturally affordable housing is critical to Oregon’s housing ecosystem because it constitutes the vast majority of affordable units in the state—approximately 75% of all affordable housing nationally is unsubsidized.¹ When new market-rate housing is built, it enables a process called filtering, where higher-income households move into newer units, freeing up older housing stock for lower-income residents. However, this supply chain breaks down when housing production is insufficient—older units remain in high demand and landlords renovate them to command higher rents, a process sometimes called “upfiltering.” Oregon’s housing shortage has accelerated the loss of naturally affordable units, as investors purchase and upgrade older apartment buildings. Some advocates argue that the best way to preserve naturally affordable housing is to build abundant new supply at all price points, while others push for policies like rent stabilization or acquisition funds to protect existing NOAH properties from conversion. Critics note that even average NOAH apartments are unaffordable to extremely low-income households, and that the term “naturally occurring” obscures the policy choices that shape housing markets.²³

Urban Growth Boundary#

The Urban Growth Boundary (UGB) is the cornerstone of Oregon’s statewide land use planning program (Senate Bill 100). It is a zoning border drawn around every city in the state that separates urban land, where high-density housing and commercial development are encouraged, from rural land intended for farming, forestry, and low-density use. Cities are legally required to maintain a 20-year supply of buildable land within their UGB to accommodate projected population growth.

The UGB has a profound impact on housing in Oregon. By constraining the outward expansion of cities, it actively promotes infill development and higher density. In theory, this leads to more multi-family units, townhomes, and smaller lot sizes within the boundary. While proponents argue this creates more efficient, walkable communities and protects Oregon’s natural landscape, critics contend that the UGB artificially limits land supply, thereby driving up land values and contributing to the state’s housing affordability crisis. The boundary is not static, however; it can be expanded through a rigorous legal process when a city can demonstrate a lack of separate buildable land to meet its housing needs.