AHS Perspectives

Arlington Approves Construction of New Detached Accessory Dwellings

Also known as backyard cottages or in-law suites, accessory dwellings are helpful tools for providing additional housing options throughout our community. Although they are not required to be rented at affordable rates, they are more likely than other new apartments to be affordable given their modest size and features.

Also known as backyard cottages or in-law suites, accessory dwellings are helpful tools for providing additional housing options throughout our community. Although they are not required to be rented at affordable rates, they are more likely than other new apartments to be affordable given their modest size and features.

On May 18, the Arlington County Board voted unanimously to allow homeowners to build new detached accessory dwellings. They also amended the County’s Zoning Ordinance to make it easier to convert existing buildings into accessory dwellings.

According to the official press release, the approved changes include:

  • Minimum side and rear yard setback distances of 5 feet for new detached accessory dwellings on interior lots; and

  • Minimum side yard setback distance of 5 feet, and a minimum rear yard setback distance of 10 feet, for new detached accessory dwellings on corner lots.

The Alliance for Housing Solutions strongly supports the County Board’s adoption of a zoning amendment to allow the creation of new detached Accessory Dwellings.

AHS recommended that the County adopt a one-foot setback for both existing and new accessory dwellings, and, should they choose not to adopt a one-foot setback, to allow a provision to “grandfather” expansions to existing buildings with smaller setbacks with the ability to expand to the allowable size and height for AD conversions as long as the expansion does not reduce the current setback. The County Board ultimately chose not to take the Alliance for Housing Solutions’ recommendations and instead adopted the staff-recommended five-foot setback.

According to ARLnow’s reporting, “A March draft of the policy estimated that 44 percent of Arlington’s one-family residential lots would be eligible to build [accessory dwellings] under these rules.”

While most anticipate that additions of accessory dwellings will happen slowly, AHS believes it is a step in the right direction to add desperately needed housing stock to our community.


Background on Accessory Dwellings in Arlington

Accessory Dwellings (ADs) can help increase rental housing options in Arlington by providing modestly priced apartments in single-family neighborhoods throughout the County.

Although they are not subsidized or rent restricted in any way, the small size and modest amenities of ADs will naturally mean they rent for relatively reasonable and affordable rents. AD rentals also provide an income stream for homeowners that can help them afford the cost of living in Arlington.

ADs can provide a valuable alternative for renters who cannot afford higher-end apartments or who prefer to live in a single-family neighborhood environment – teachers, caregivers, recent college graduates, retirees and others.

Since 2009, ADs located within single-family homes have been allowed in Arlington, and in 2017 the County Board approved conversion of existing detached accessory buildings (garages, offices, etc.) to be used as ADs, as long as only internal renovations are needed.

The May 18, 2019, decision allows construction of new detached ADs.

Arlington’s zoning ordinance allows construction of any detached accessory building not used as housing (detached garages are most common), one foot from the side and rear property lines. There are thousands of these buildings throughout Arlington’s single-family neighborhoods – County staff has estimated about 4,500 existing garages, half of which are located one foot from the property line.

Even with this existing rule in place existing buildings located less than five feet from the property line would be limited to the current rule of only internal renovations even if they are substantially smaller than what is otherwise allowed. A small existing building could be expanded to create a larger garage, but not a larger Accessory Dwelling.


Rationale for Recommended One-Foot Setback

The following is an excerpt from the letter AHS sent to Arlington County Board prior to their May 18, 2019 decision.

1. Consistency and simplicity

County zoning rules are already confusing for homeowners and contractors to navigate. Keeping AD rules consistent with the rules for other accessory buildings such as garages will create a much more easily understandable system of rules and reduce the potential for inadvertent violations. Confusing and limiting rules could also cause homeowners to give up pursuing an Accessory Dwelling in the first place. We know this was the case after the adoption of the original AD ordinance that went into effect in 2009 – less than 20 of these units were created in the decade following enactment. This was the main driver for the updates approved in 2017, which simplified the regulations and removed barriers. After this experience, we should not set up a similar situation with detached ADs that will approve them in concept but create unreasonable rules that limit their creation.

2. Equal treatment for cars and people

The proposed setback rules for ADs will create a system in Arlington that favors creating garages over creating apartments. Developers who build new homes, many of which are including detached garages due to favorable lot coverage rules, may decide that the five-foot setback requirement is too limiting and will instead build a more standard garage as an accessory building. Owners of existing garages will have the ability to expand their garage to accommodate more cars and a playroom or office, because the rules allow for an accessory building to be up to 560/650 square feet (depending on the zoning district) and up to 1.5 stories tall.

3. Larger setbacks should be optional, not required

The Virginia building code requires that any dwelling unit with a setback of less than five feet have certain fire-resistance ratings and a limited number of wall openings (windows and doors). Those with setbacks below three feet are not allowed any wall openings. So even if Arlington requires only a one-foot setback these other rules will be in place to limit the impact of the buildings on neighbors in terms of both safety and privacy.

Some owners considering an AD will decide that a larger setback will be worth the trade-off to avoid complying with these fire safety regulations, which do increase the costs of construction and renovation. Other owners will find a 1-foot, 2-foot, 3-foot, or 4-foot setback is needed to make the building feasible for any number of reasons such as design, consistency with existing structures, locations of trees, etc. This should be something that each owner decides based on their individual circumstances. Providing maximum flexibility will create the greatest number of ADs and the greatest impact on housing options and affordability in Arlington.

4. A smaller setback will accommodate more conversions of existing buildings

In earlier public meetings on this issue, staff shared an estimate of 4,500 existing detached garages in Arlington, with half of these garages at a one-foot setback from the property line. Although we do not have data on the specifics, it is very likely that the vast majority of the remaining half of these garages are also at setbacks less than the five feet that is recommended by staff.

Enacting a five-foot setback requirement for newly constructed ADs would then place almost all existing detached garages into a limited “grandfathering” status where conversion to an Accessory Dwelling could be done with only internal renovations. Because many of these existing garages are small, one-story structures they may not be suitable for use as an AD without some sort of expansion. As noted above, these structures could be expanded at their current setback in order to create a larger garage, but under the staff’s proposal they cannot be expanded if the building will be used for an AD.

A result of this grandfathering limitation could be that more existing garages are demolished in order to create new structures at the five-foot setback. Any infrastructure associated with the existing structure – driveways, walkways, electricity and plumbing, would also have to be moved and would create more disruption to existing neighborhoods than would a more limited expansion of the existing structure. Allowing greater flexibility for expansions of existing structures could help reduce the need for these demolitions and would likely result in a greater number of conversions taking place.

5. Several other communities use a setback of less than five feet

The staff’s Board Report on this proposal provides a summary of setback standards in other jurisdictions (see p. 6 of the report). While very few of the jurisdictions shown allow the setback of one foot, and five feet is the most common, there are several that require less than five feet in many circumstances:

  • Washington, D.C. does not specify a minimum setback

  • San Jose allows no setback for the first story

  • Minneapolis allows three feet in most circumstances

  • Santa Cruz allows three feet for one-story structures

  • Berkeley allows four feet

We note that the staff’s analysis chose to consider only a one-foot, five-foot, or ten-foot setback rather than a more refined sliding scale that would have considered a setback such as three feet. Should the County Board decide not to adopt the one-foot setback standard that we are recommending, AHS urges consideration of a more refined approach with a compromise such as three feet. Although it would not capture most of the existing structures (as our recommendation would), the three-feet compromise would meet many of the goals specified by staff in selecting the five-foot setback while still allowing maximum flexibility for at least a portion of the existing accessory structures to be converted. As we noted above, three feet is also the limit in the building code for allowing any wall openings along the side facing the setback, so this compromise has some basis in existing regulations.


The Alliance For Housing Solutions periodically sends policy/action alerts to let constituents know about upcoming decisions that affect housing affordability in our community. These emails include AHS recommendations and information about how to make your voice heard.

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