SpaceEfficientHousingCover.JPGReport: ​
Housing Options for Single-Dwelling Neighborhoods

Intended or not, many zoning codes in Oregon tend to encourage the development of large, detached homes in residential neighborhoods to the exclusion of anything else. Research by the Oregon Department of Environmental Quality found building smaller homes was among the best practices to reduce the lifetime carbon and energy impacts of single-dwelling housing. When combined with an appropriate mix of uses, denser housing configurations also support more walkable and less auto-oriented communities. Demographers expect the trend towards smaller households to continue, and many parts of Oregon are experiencing a critical lack of affordable housing. Collectively, these observations motivate research into space efficient housing models, and methods of supporting their production.

Building on that research, DEQ and the Transportation and Growth Management Program commissioned a report on how to encourage more space-efficient housing options in Oregon's cities.

The full report is here (10mb PDF).

The executive summary follows.

Executive Summary (Overview)

The housing types described in this report support higher population densities in single-family neighborhoods in ways that maintain neighborhood character and increase housing options. The housing types studied include:

  • Cottage clusters
  • Internal division of larger homes
  • Corner duplexes
  • Accessory dwelling units

In Oregon, urban populations are growing, household sizes are shrinking, and housing prices are rising.  Pressures to expand urban growth boundaries in some areas are balanced by efforts to reduce carbon impacts from the housing and transportation sectors. Single-family zoning is still a dominant land use in most Oregon cities. In fact, within the Portland Metro urban growth boundary, single-dwelling residential zones make up 48% of all land area and 77% of all land area currently zoned for housing.  As Oregon cities grow, it is anticipated that smaller housing options, such as those outlined in this report, will grow in importance for single-dwelling residential zones.

These traditional housing types have been selected specifically for their small size and ability to nestle discreetly and compatibly within existing neighborhoods of detached, single-unit homes.

Many Oregon communities have already experimented with legalizing one or more of these housing types, or re-legalizing where once allowed. This report provides case studies, analyzes codes, and recommends best practices.

Executive Summary (Recommendations)

General recommendations across all four housing types

  • Allow by-right or through a simple land use process;
  • Allow in all single-dwelling zones;
  • Minimize off-street parking requirements;
  • Customize use restrictions and design compatibility requirements (if any) based on local priorities and concerns;
  • Balance regulatory restrictions against desired housing production levels; and
  • Periodically review and update regulations based on actual production levels and community feedback (positive and negative) from completed projects.

Specific recommendations by housing type

Cottage Clusters

  • Couple density bonuses (up to 2x) with home size caps;
  • Avoid minimum lot size requirements for the entire cluster and for individual lots within it;
  • Support community-oriented site plans (e.g., homes fronting on shared central courtyard; vehicle access and parking at periphery) with flexible subdivision regulations or by allowing multiple homes on a single lot through a discretionary review (e.g., planned development) process; 
  • Balance strictness of layout and design requirements with the demands of neighborhood compatibility and the flexibility required by the market to see cottage cluster provisions get used in practice.

Internal Division of Larger Homes

  • Expand application of provisions currently applied to historically-designated homes to any older home exhibiting key characteristics (quality materials, neighborhood character); and
  • Expand or drop zoning code definitions of “household.”

Corner Duplexes

  • Allow attached housing and increased density (up to 2x) on corner lots;
  • Consider individual or combined size limits on new corner duplex homes so their collective massing is similar to that of a single large house; and
  • Provide the option of subdividing corner lots with duplexes into two fee-simple lots.

Accessory Dwelling Units (ADUs)

  • Avoid owner-occupancy and special use requirements (e.g., restrictions on home-based businesses, affordable housing deed restrictions, short term housing*);
  • Ensure resulting property tax increases, if any, are not so large as to serve as a deterrent to building;
  • Consider allowing both a detached and an attached ADU on the same lot; and
  • Provide more flexibility in size, allowing for both very small and larger ADU types.

Read the complete report (10 mb PDF)