Accessory apartment in a backyard in NE Washington, DC. Image by author.

The District government is working to make an accessory apartment (or accessory dwelling unit or ADU) a bit easier to build. The legalization of accessory apartments as part of the 2016 zoning regulations update was a landmark change, but advocates have asked for more restrictions to be lifted. Now, the DC Zoning Commission has expressed interest in doing just that.

In addition to zoning, DC has streamlined the process for reviewing building permits for one and two family projects. To provide direct help, the District government is launching a $1.4 million DC homeowners assistance program. The program will provide technical and financial assistance for low- and moderate-income homeowners, and also support the creation of income-restricted units by higher-income homeowners who take advantage of the assistance (details TBA).

Eased zoning rules for accessory buildings

Last year the DC Zoning Commission eased two important height and setback rules. An accessory building (like a garage, carriage house, or backyard cottage) is now allowed to be 22 feet tall rather than the old limit of 20 feet. The 2 story limit remains the same. The accessory building is also now permitted to be set back from the middle of an alley by only 7.5 feet, instead of 12 feet (see figure 7). These changes cover accessory buildings in both R and RF zones (to understand different residential zones, see the UPO-CSG ADU DC Homeowner’s manual, Chapter 4). We’ve updated the ADU DC Homeowner’s manual to reflect these changes.

Updated figure of accessory building zoning regulations (2021).

In this action, the Commission also clarified that the zoning regulations do not permit an accessory building (other than a shed) to be constructed as a matter of right in the required rear yard (see figure 7). The Office of Planning believes that DC has many deep lots where an accessory building can be located outside the required rear yard. However, a number of architects have expressed concern that the variably enforced rule will now discourage new ADU construction. Though the Board of Zoning Adjustments (BZA) routinely approves these kinds of requests as a “special exception,” the process requires additional time and cost.

Other zoning reforms could boost ADU creation

While the modest changes to height and setback requirements for accessory buildings in the backyard are welcome, we have a longer list we hope the Zoning Commission will consider. The Commission has indicated that it wanted to address additional reforms to lower barriers to building ADUs, but it has yet to take up the matter.

Our two top reform proposals that have a good chance of getting approved are:

  • Eliminate the five-year waiting period on new construction for accessory buildings used as dwellings in Residential Flat (RF) zones (RF are rowhouse zones, no waiting period is imposed in R zones) and;
  • Allow accessory buildings used as living units to have a larger footprint than the current 450 square foot restriction.

These two top suggested changes to the zoning regulations could facilitate increased production of additional accessory apartments and second dwellings while still respecting the intent of the zoning regulations and Comprehensive Plan. Here’s our rationale for these reforms.

Eliminate the five-year delay for construction and occupancy of a second dwelling in an accessory building in Residential Flat (RF) zones: In RF zones, the zoning regulations require a five-year waiting period before an expanded or new accessory building can be used as a dwelling (DC Zoning Regulations of 2016, Subtitle U-301.1(e). This is especially confusing because the RF zones typically permit two dwellings as a matter-of-right.

The five-year limit unnecessarily and arbitrarily restricts the ability to construct and occupy a new accessory building, including constructing a living unit in a new garage which itself can be built as a matter-of-right. While the Board of Zoning Adjustment could waive the requirement by approval of a special exception, the delay, cost, and unpredictability of the special exception process can deter many homeowners. RF zones, given their similarity to the R-3 zone (which is single-family rowhouse zone), should be given the same allowance for new construction of an accessory building that otherwise conforms to the zoning regulations.

Revise the 450 square foot footprint limit for an accessory building used for a dwelling to permit up to 650 square feet: The maximum building footprint for an accessory building is limited to 450 square feet or 30% of the square footage of the required rear yard area, whichever is larger (DC Zoning Regulations, Subtitle D-5006.1). In most cases, 450 square feet will be larger.

A 450 sq. foot building area allows for a studio apartment that can provide minimal accessible clearances for wheelchairs. The limit undermines a key benefit of ADUs — providing a space to age in place or a new home for a person with physical disabilities. Revising the 450 square foot requirement would be closer to the Office of Planning’s original recommendation of 900 square feet. Many lots offer room for footprints of 900 square feet, and other zoning regulations would restrict the total permitted lot occupancy of all occupied structures on the property. We recommend a 650 sq. foot building area as a matter-of-right to provide flexibility for a one-bedroom unit that could accommodate conditions such as an aging-in-place couple or a parent and child with a disability.

Permitted as a matter-of-right (no needed special review), this action could incentivize accessible, universally designed units. This facilitates preparation for increased housing options for those with mobility impairments and assistive devices. Removing the 450 sq. foot restriction for dwellings in an accessory building while relying on existing lot occupancy limits would allow greater design flexibility and the ability to meet the needs of occupants.

We have a longer list of reforms and their detailed explanations here.

We’ve made good progress towards untapping the potential of creating smaller, lower-cost homes that are woven into the fabric of our DC neighborhoods. We hope to get these zoning reforms before the Zoning Commission this or early next year. We expect to get pushback from certain members of our community, but given the changes in attitudes about exclusionary zoning, we are optimistic we can lower unnecessary barriers to these new housing opportunities that benefit both renters and homeowners.

Learn more about how you can build your ADU

Do you have an idea for an accessory apartment for your DC property but don’t know where to start? You can request a 15-30 minute phone conversation with an experienced architect to discuss your project idea. CSG is partnering with United Planning Organization (UPO) to set up these homeowner education sessions. Low-income and BIPOC homeowners are especially encouraged to sign up. Sign up here. Also, if you want to join the conversation about ADUs in DC, join the online forum for homeowners and professionals here.

This post was written with support from the United Planning Organization (UPO) as part of an ongoing collaboration to educate DC homeowners about the opportunity to build an accessory apartment.

Disclosure: The author is on one of the teams for the District’s Residential Accessory Apartments Program application.

Cheryl Cort is Policy Director for the Coalition for Smarter Growth. She works with community activists, non-profit groups and decision-makers to promote more walkable, bikeable, inclusive, transit-oriented communities as the most sustainable and equitable way for the DC region to grow and provide opportunities for all.