Image by ep_jhu used with permission.

As I discussed yesterday, zoning is a powerful tool but it can’t do everything — and it’s misused far too often. When used properly, zoning controls how land is used and guides the pattern and shape of development within a jurisdiction.

Unfortunately, since zoning is ubiquitous throughout the development process, elected officials often try to use zoning legislation to coax developers in a different direction and to address community complaints — regardless of whether it's really the best mechanism to do so. Here's a breakdown of what zoning can actually do well:

Zoning can regulate how land is used

Zoning is most often used to separate different types of uses (e.g. residential, commercial, industrial) to limit the negative impacts of one use on the surrounding properties. For example, a residential zone would prohibit a landfill from being built because the landfill would likely smell, there would be increased truck traffic, garbage could spill over into nearby natural resources, etc. All of this would be detrimental to the health safety and welfare of the residents in the area. When zones are separated by their basic use, this is known as Euclidean Zoning.

Zoning can effectively control uses, because once a zone is established the elected officials can easily determine which specific uses can be permitted and which should be prohibited. For example, in Montgomery County, Major Vehicle Repair (an industrial use) is permitted in the three different industrial zones, but it is prohibited in all the residential zones. Conversely, Single-Unit Living (a residential use) is permitted in all the residential zones, but none of the industrial zones.

Residences next to an industrial plant in southeast DC. Image by JY O’Reilly used with permission.

However, local governments are not required to strictly separate uses. It is very common for communities to have zones that allow for multiple uses. In addition to the Euclidean Zones, Montgomery County also has “Commercial/Residential” zones, where like the name suggests, commercial and residential uses are permitted.

For example, in the Commercial/Residential zone, both Multi-Unit Living (a residential use) and Retail Service Establishment (a commercial use) are permitted. These types of zones are valuable because property owners are not limited to one type of use and can figure out what’s best for their land. Multiple-use zoning is beneficial for communities because it reduces the distance between destinations, such as housing, offices, retail, and parks.

Zoning can regulate the general form of buildings

Zoning can effectively regulate a building’s size in relation to the lot it is located on, often referred to as the building’s massing. Three dimensional standards are used to regulate this.

First, a “set-back” determines the distance between the building’s front, rear, or side and the edge of the property line. If a zoning district has a large front set-back, the building will have a large front yard. If the zone has a zero side set-back, it means that two buildings can be built right up against each other, like rowhomes in DC.

Second, the zoning ordinance can regulate the height of a building. This was designed to help keep sunlight at the street level and stops skyscrapers from being built next to bungalows.

DC is notorious for its height limits. Image by BeyondDC licensed under Creative Commons.

Lastly, zoning ordinances regulate the lot coverage, which is the percentage of a lot that is covered by the development. This differs between places, but generally includes the building, parking lot, and driveways. A lower lot coverage percentage means there will be more open space in a neighborhood.

For example, Arlington’s R-20 zone, which is for one-family dwellings and can be found in the County’s northwestern tip, has lot coverage of 25 percent. That means a quarter of the property can be covered by the house, leaving lots space between buildings. Arlington’s RA7-16 zone, used for multi-family dwellings and found in between Metrorail stations along Wilson Blvd, does not have a lot coverage maximum so development can cover the entire lot.

Zoning can regulate the intensity of a use

Zoning ordinances can also effectively control a development’s intensity. Intensity refers to how much of a use is allowed in the zone. Intensity is generally controlled by the building density or the Floor Area Ratio. Building density generally refers to the number of residential dwelling units in an acre.

In Alexandria, the R-20 residential zone permits single-family homes on 20,000 square foot lots, or roughly two dwelling units per acre. In the RA/Multifamily zone, a multifamily building can have up to 27 dwelling units per acre. That means the RA/Multifamily zone has a higher intensity than the R-20 zone.

In addition to building density, the Floor Area Ratio (FAR) is used to measure the level of non-residential intensity of a development. The FAR is computed by comparing the square footage of the lot and the total square footage of the building. If a development’s FAR is one, it means the square footage of the building is equal to the square footage of the lot the building sits on.

Open space in Alexandria, Virginia. Image by airbus777 licensed under Creative Commons.

It is important to note that the FAR is not equal to lot coverage, because the building’s square footage can come from multiple floors. In Alexandria, the FAR in the Commercial Service Low zone is 0.5, meaning a one-story commercial building can be half the size of the property. In the Commercial Downtown zone, the FAR is 2.5, meaning a commercial building can cover the entire property and be 2.5 stories, or more likely would not cover the entire property, but be multiple stories high (such as cover half the lot and be five stories tall).

Zoning can guide the environment surrounding a building

Lastly, zoning is effective to regulate the built environment on scale that is beyond an individual building. For example, zoning regulations can be designed to create a walkable streetscape. Zoning can do this by regulating specific features of the individual properties. Zoning can regulate buildings and properties to have shorter lot widths, a minimum percentage of windows on a building’s front, a maximum distance between building entrances, and small building features such as recessed entrances or second floor balconies.

These regulations contribute to creating a pedestrian environment that is visually compelling to someone walking by. It creates something new to look at from building to building and opportunities to linger in an area.

Prince George’s County is currently rewriting their zoning ordinance, and is including new zones that specifically encourage walkable development. The Transit-Oriented and Activity-Center zones are designed to serve as accessible focal points for neighborhoods and encourage walkability to support a mix of uses — an example of zoning used right.