FAIRFAX CITY — At a Planning Commission work session on Oct. 13, city planning staff presented detailed options for whether Fairfax City should allow detached accessory dwelling units — small, separate housing units in the rear yards of single‑family properties — and asked the commission whether staff should continue developing a draft ordinance and what standards should be prioritized.

The presentation summarized current policy and ordinance language, potential physical and operational standards, and tradeoffs. Planning staff said the city already allows attached ADUs but not detached ones, and framed the question as whether and how to expand permissions while protecting neighborhood character.

"In everyday terms, the definition says that an ADU is a full dwelling unit, that it's part of another house, and that it's subordinate or that it's accessory to the main house," planning staff said during the presentation. Staff also noted overlap with other ordinance terms: the acronym "ADU" is already used locally for "affordable dwelling unit," and the city might choose a different label if it moves forward.

Why it matters: Detached ADUs can add housing stock and provide options for seniors and college students, while also raising concerns about neighborhood character, parking, impervious surface and enforcement. The commission’s discussion focused on technical standards that would shape those tradeoffs — setbacks, height, floor area, lot coverage, parking and occupancy rules — and on where such units would realistically be feasible in the city.

Key facts and staff estimates

- Staff estimated roughly 5,200 detached houses and duplexes could theoretically be candidates for detached ADUs, and said about 1,000 of those are in homeowners‑association areas likely to preclude detached ADUs. After excluding properties with small yards or other constraints, staff estimated roughly 3,000–3,500 properties might be realistically able to accommodate detached ADUs under many standard setback/coverage assumptions.

- Existing related provisions in the zoning ordinance that staff proposed could be extended or adapted for detached ADUs include: a 5‑foot minimum setback from a lot line for accessory structures; a 12‑foot maximum height for accessory structures located in required side/rear yards (measured per ordinance rules at the midpoint between eaves and ridge); a requirement that ADUs remain accessory in size (the current attached‑ADU rule limits ADU floor area to 35% of the main house’s square footage); accessory‑structure footprint limits (no more than 50% of the main house footprint for garage‑type structures); and a rule that combined accessory structures may not exceed 30% of the required rear/side yard area.

Standards and options discussed

- Setbacks and separation: Staff illustrated how a 5‑foot lot‑line setback (current accessory structure standard) or a larger separation from the main house (for visual separation) would change where a detached ADU could be placed on a typical lot.

- Height: The commission discussed whether to restrict detached ADUs to one story (or one‑and‑a‑half) in many settings, or allow two‑story ADUs in larger lots. Staff explained how the ordinance measures height (midpoint between eaves and ridge, with adjustments for slope), which can make measured height different from perceived height.

- Size controls: Staff noted the difference between footprint and gross floor area limits and recommended using both if multiple stories are allowed, to prevent large multi‑story units that overwhelm the lot.

- Lot and building coverage: Staff reviewed citywide building‑coverage and impervious‑surface rules, and the accessory‑structure cap (30% of combined required rear/side yards) intended to keep backyards predominantly open.

- Parking and occupancy: Commissioners raised concerns about on‑street parking pressure and enforceability. The current ADU rule limits ADU residents to no more than two vehicles, but staff said that rule is difficult to enforce because it requires proving vehicle use by ADU residents. Commissioners suggested requiring physical on‑site parking spaces or other parcel‑based solutions rather than vehicle counts.

- Nonconforming structures and conversions: Staff flagged a common question — whether existing garages or other accessory buildings that sit within 5 feet of a lot line or are otherwise nonconforming could be converted to ADUs, and under what conditions (for example, whether enlargements or modifications would be allowed). Commissioners stressed this will be a detailed policy choice.

- Design review: Staff recommended against applying an architectural design‑review requirement for ADUs (the city’s BAR does not review detached houses) and suggested dimensional controls, bulk‑plane angles or window‑placement rules as alternatives to achieve compatibility without creating a new, burdensome review process.

Neighbors, equity and enforcement

Several commissioners argued for mapping and data to target where detached ADUs would be most feasible and most likely to serve intended populations rather than primarily increasing investor‑driven rental supply in high‑cost neighborhoods. One commissioner urged staff to analyze lot geometry, impervious surface layers and parking constraints; another asked staff to consult the fire marshal about emergency access and egress requirements. Dr. Rice suggested in‑house GIS staff could produce a suitability map and noted specific staff ("Jason and Amy Lindenney and some of the folks in CDP…") who could assist.

Comparisons to nearby jurisdictions

Staff summarized regional precedents: Arlington and Alexandria have allowed detached ADUs (Arlington earlier, Alexandria in 2019 and 2021 respectively), Fairfax County has restrictive rules tied to lot size, and several nearby towns (Falls Church, Herndon, Leesburg) have ADU ordinances. Commissioners observed that setback, height and occupancy rules vary across jurisdictions and that Alexandria’s approach reflects its particular townhouse/dense‑lot context.

Commission direction and next steps

Commissioners did not vote on a policy change. They asked staff to: prepare a mapping‑based analysis showing parcels that could realistically accommodate detached ADUs given setbacks, lot geometry, impervious/coverage constraints and HOA overlay patterns; consult with fire/emergency services about access and safety requirements; and report back with comparative examples from nearby jurisdictions and potential draft standards. Staff also said they will brief City Council in a forthcoming joint work session if the commission requests further study.

"We could do something like that," staff said in response to requests for mapping and additional GIS analysis. "I will flip back here and I'm anxious to hear, some opinions from the Commission," the staff presentation ended, prompting commissioners to identify priorities.

The commission signaled interest in continuing study rather than advancing an immediate draft ordinance. Commissioners emphasized the need for targeted data, enforceable parking/occupancy rules, and careful attention to neighborhood compatibility if detached ADUs are permitted.

Next steps: staff will produce mapping and background materials and present a summary to the commission and to City Council in a forthcoming work session. No zoning amendment or council action was taken at the Oct. 13 meeting.