Fairfax City planners weigh detached accessory dwelling units, ask staff for mapping and technical guidance

Fairfax City Planning Commission members spent their Oct. 13 work session examining whether the city should permit detached accessory dwelling units, or ADUs, and what zoning and operational standards would be needed if it does.

Staff planner Mr. Foreman opened the discussion with an overview of current rules and options, saying the city already allows ADUs that are part of a main house but not separate backyard or detached units and that, if pursued, "there's a whole lot of details that go along with allowing detached ADUs." He told commissioners the goal of the session was to get guidance on whether to continue studying detached ADU standards and which standards the commission should prioritize.

The question matters because the citywide housing assessment and the Fairfax City Comprehensive Plan include recommendations to expand opportunities for ADUs while ensuring they "do not negatively impact the surrounding neighborhood," a phrase Mr. Foreman repeated during his presentation. Staff emphasized the issue is detail-heavy and overlaps with existing rules for accessory structures such as detached garages.

Key facts and constraints discussed - Eligibility estimate: Staff estimated about 5,200 detached houses and duplexes in the city could theoretically be candidates for ADUs, with roughly 1,000 of those in homeowners association (HOA) situations likely to preclude ADUs. After accounting for small lots and setback constraints, Mr. Foreman said a reasonable working estimate is "maybe 3,000 to 3,500" properties that could physically accommodate a detached ADU. - Existing ADU and accessory-structure standards: Under current zoning, ADUs must be part of the main house (attached), owner-occupied, capped at 35% of the main house's gross floor…