Determining Density for Housing:

Land Use Policies, Bulk Controls, and Lot Sizes

As communities across the United States grapple with persistent housing shortages and rising affordability pressures, longstanding local zoning codes and land use planning policies are being reexamined. Three interconnected policies, though distinct, regulate how much housing can be constructed on a given parcel of land. Lot sizes per use designation determine how many homes of which type are permitted within a particular area, bulk controls govern the size and form of buildings, and other land use policies can further impact how the land can be used.

LOT SIZE AND DENSITY

Lot size is the most straightforward regulation for controlling housing density. Minimum lot size requirements dictate the smallest allowable parcel of land on which a particular form of housing can be constructed. Larger minimum lot sizes reduce the number of homes that can be built per acre, thereby reducing density.

Housing type does influence lot size. Townhomes, for example, require far less land per unit than a single-family detached dwelling due to the lack of side setbacks for middle units. A multi-family structure – condominium, apartment, co-op, or assisted living center – will often require a larger lot than a single-family dwelling, due to larger floor plate, parking mandates and setbacks.

Density is also described as a value of units of housing per acre (du/ac). This figure is most commonly used for multi-family construction, new subdivisions, and comprehensive plans. Units per acre can be calculated as both units be gross acre (before land use dedications) as well as units per net developable acre (post-land use dedications).

BULK CONTROLS

Bulk controls govern the shape, scale, and siting of buildings on a lot. These controls are typically included in local zoning ordinances and work in tandem with density standards to define what can—and cannot—be built. Bulk controls can constrain housing supply by limiting the size or number of units that could otherwise fit within a lot or development.

 Key examples of bulk controls include:

  • Setbacks: Setbacks require buildings to be set back a minimum distance from the front, rear, and side lot lines.
  • Height Limits: Establish the maximum allowable height in a given zone.
  • Floor Area Ratio (FAR): FAR defines the allowable building floor area as a proportion of the lot area.
  • Lot Coverage: Limits the percentage of a lot that may be covered by impervious surfaces, including the building envelope and any impervious surface, such as a driveway or sidewalk. Lot coverage is often established as a percentage of the lot surface but may also be square-foot-based.  
  • Building Envelope: Some jurisdictions define a three-dimensional building envelope within which all development must fit, combining height, setback, and other rules. This can include building articulation, footprint, and elevation design standards (which regulate the building’s dimensions in proportion to specific features).
  • Unit Size: Established minimum unit sizes can affect density, especially in multi-family dwellings.

ADDITIONAL LAND USE POLICIES

Additional land use policies, such as those listed below, can further reduce the amount of developable land on a site.

  • Parking Mandates: For both single-family and multi-family construction, the amount of required off-street parking will influence how many units of housing can fit in a given area. Parking mandates can also specify if the required parking is enclosed or open-air.  
  • Street Width: For new subdivisions, requiring extra-wide streets will reduce the amount of net developable acres, as well as increase the amount of impervious surfaces.
  • Buffers: Buffers serve as a sort of setback to separate development. When a municipality requires buffers, this unusable land can further reduce density by reducing the amount of net developable acres.
  • Stormwater: Beyond the lot coverage/impervious surface limit noted above, the amount of space designated for stormwater management can reduce the amount of usable land, particularly at the subdivision level.
  • Parks and Green Space: Parks, trails, and green spaces will reduce the amount of developable land at the subdivision scale.

REGULATORY INTERPLAY

While lot size, housing typology, bulk controls, and related land use policies serve different regulatory functions, their cumulative effect can and does have a significant impact on the feasibility of new housing and the cost of construction. Regulatory interplay, the ability for these policies to work in concert with one another to deliver the housing type and density allowed without conditional approval, is essential.

Consider the case of triplexes in Minneapolis, which in 2018 became the first major city to allow for a range of housing options citywide. Although up to three units are allowed on any residential lot, strict bulk controls—notably low FAR limits—continued to restrict where triplexes could be built:

“The two interior districts each have a 28-foot height limit and a FAR limit of 0.5, meaning that a house on a standard 5,000 square foot lot can be no bigger than 2,500 square feet. This makes it a lot harder for developers to build duplexes and triplexes in those areas.These restrictions may have been part of a necessary political compromise: allowing duplexes and triplexes in all neighborhoods, but preventing them from being any larger than nearby single-family homes in certain areas.”

Yudhishthu, Zakary. “Minneapolis’s Natural Upzoning Experiment” Metropolitan Abundant Project. June 2024

The Minneapolis example illustrates how a limited floor area ratio can block the allowed use of triplexes on a 5,000 square foot lot.

Beyond this example, there are additional ways in with the lack of regulatory interplay can work against the goal of a community’s land use policies:

  • Elevation Requirements, Parking and Setbacks: In a community that regulates the appearance of a home in proportion to its garage sizes, the size of the required enclosed parking could require a wider home
  • Height, FAR and Impervious Surfaces: With low height and low impervious surfaces, it is possible that a multi-family structure may
  • ADU, Parking and Impervious Surface: Requiring additional parking for an ADU could increase the amount of lot coverage beyond what is allowed.

POLICY CONSIDERATIONS

Regulatory interplay is critical to well-functioning zoning codes and local land use policies. Without alignment zoning, land use, and related local planning policies, even well-intentioned land use policies can be undermined by conflicting or duplicative processes. Whether intentional or inadvertent, the lack of regulatory interplay will drive projects to the discretionary approval process, which can result in decreased density and increased costs.

As policymakers seek to promote housing production and increased affordability, regulatory flexibility via a more integrated regulatory framework can deliver greater density and le. Achieving this alignment is not just good government, but also improves project feasibility and predictability.

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