One of the primary goals of the Smart Growth movement is to create density where development already exists, which can prevent sprawl and preserve greenspaces. Smart Growth Maryland is eager to encourage infill redevelopment, which takes underutilized lots and land in urbanized areas and returns them to efficient use. While the concept is straightforward, there are a number of approaches to accomplishing effective infill redevelopment. Read on to find out more about four common initiatives communities across the countries use to encourage infill.

But first, a Brief History of Zoning 

While there are a number of obstacles to infill redevelopment, primary among them are zoning laws. The first zoning laws in the United States date to 1916. Early laws were what are known as single-use zoning laws, which regulated the scale and use-type of buildings in a community. Common uses were single-family residential, multi-family residential commercial, and industrial. This type of zoning is also known as Euclidian zoning, after the landmark Supreme Court Case, Euclid vs. Ambler (1926), which affirmed their constitutionality. While advocates argued that Euclidian zoning would make cities safer and more pleasant for residents, research has shown that it often encouraged sprawl, making neighborhoods less equitable, less sustainable, and less walkable in the process. 

The consequences, intended and unintended, of Euclidian zoning are among what the Smart Growth movement aims to remedy, particularly through the development of effective infill policies and incentives. Here are a few common policy changes communities are using to create density in already developed areas. 

1. Eliminating Single-Family Zoning

Missing Middle Housing Types, Opticos Design Inc

Single-family zoning has historically excluded lower income, often minority, residents from certain neighborhoods since they could not afford single family homes. Advocates argue that eliminating single-family zoning (also known as upzoning) is one step communities can take to create more equitable and affordable neighborhoods. Upzoning can help fill what’s known as the “missing middle,” or more affordable residential units that fill the gap between large multi-story apartment buildings and single family residences. Residence types such as duplexes, triplexes, and small-scale apartment complexes are more affordable to low- and middle-income families. Historic districts lend themselves to this type of housing and the goals of upzoning frequently overlap with the goals of historic preservation. Preservationist Jacqueline Dryer argues that upzoning large historic homes, such as those in the Germantownneighborhood of Philadelphia, can make them more affordable to live in and maintain, as well as more sustainable, with energy costs split between multiple families. These types of policy changes create density while maintaining neighborhood character and add to the housing stock without developing vital greenspaces. 

Community Highlight

In April 2023, Arlington County, Virginia voted to eliminate single-family zoning to increase “missing middle” housing and make the county more accessible and affordable to a diverse array of residents. 

2. Instituting Form-based Code

Over the 100 years since the enactment of the first U.S. zoning laws, alternative zoning-types have become popular, including Form-Based Code or Form-Based Zoning. According to the Form-Based Code Institute, this type of zoning law “fosters predictable built results and a walkable public realm by using physical form—rather than separation of uses—as the primary basis and focus for the code and standards.” From the outset, the development of form-based codes solicit and include community input and visions. This results in more pedestrian-centered, mixed-use cities and neighborhoods, encouraging lively streetscapes which supply the majority of residents’ daily needs. 

Community Highlight

South Bend, Indiana recently won the Driehaus Form-Based Code Award for exemplary development and implementation of form-based code. Closer to home, Frederick, Maryland just announced its first draft of a form-based code to redevelop the East Street Corridor into a mixed-use area. 

3. Eliminating Mandatory Parking Minimums

As mentioned above, creating more walkable and accessible neighborhoods is one of the major goals of form-based code. One powerful strategy to accomplish this is eliminating mandatory parking minimums. Parking minimums typically require developers to dedicate a certain amount of lot space to parking, which can significantly decrease the amount of usable land and significantly increase the cost of the development. There are a number of benefits to eliminating these minimums, including more efficient use of infill lot space. Furthermore, since the cost of parking lots are often passed on to building tenants and the public, eliminating parking minimums can create more affordable housing and commercial space in a community. 

Community Highlight


Pike & Rose, a mixed-use development in Montgomery County, sits on the former site of a 24-acre strip mall. The majority of the lot was once surface parking.

 While some communities in Maryland have reduced parking minimums in recent years, none have completely eliminated them. Richmond, Virginia, however, provides a recent example of a major  metropolitan area to vote to eliminate parking minimums in an effort to curb sprawl and increase housing supply and affordability.

4. Allowing for Accessory Dwelling Units


Accessory dwelling unit in Portland, Oregon

Allowing for accessory dwelling units, commonly known as ADUs, is another common tactic used to promote infill and create density. When advocates refer to ADUs, they’re typically referring to things like in-law suites, above-garage apartments, English basements, or tiny homes – units that can exist on the same lot as the primary residence. Not only do ADUs increase density, they can also increase the variety (in terms of cost and type) of the housing options in a community, particularly in dense areas like historic districts. ADU construction is not a cure-all for the housing-crisis and policies like mandatory parking minimums and single-family zoning can make ADUs difficult or impossible to build in many communities. However, used in concert with other Smart Growth policy changes, such as those described above, allowance for ADUs can allow for more effective land use decisions when it comes to creating affordable and dynamic communities. 

Community Highlight

Many counties in Maryland allow for ADUs including Montgomery, Prince Georges, and Howard Counties. In 2021, Frederick County voted to allow by-right ADUs and in 2023 the Maryland State Legislature voted to create a task force to study and expand ADUs in the state.