Accessory Living Unit Rules Under Review, February 2026

Fairfax County’s Department of Planning and Development is conducting public outreach to review its policies towards Accessory Living Units, and MCA attended a recent presentation led by Carmen Bishop and Casey Judge of the Planning Department.
Accessory Living Units (ALU), sometimes known as “In-Law Suites,” describe attached or detached additions to existing homes that are typically used for family, au pairs, or renters. The county defines them as “a second-ary dwelling unit established in conjunction with and clearly subordinate to a single-family detached dwelling unit,” with areas for eating, sleeping, living, and sanitation.
Previous surveys of Mantua residents have found that neighbors support rules that allow them to create multi-generational housing and to age in place. Mantuans in support of ALUs note that they can reduce the need for tear-down-and-rebuild projects, where additional square footage can be done by right.
Current standards for ALUs were put into place in 2021, and since then, only 24 have been approved by special permit, making them a rarity in Fairfax. Residents must have 2+ acres to have a detached ALU, and are limited to two people, two bedrooms, and a maximum size of 800 square feet or 40% of the size of the home if attached, and 1,200 square feet if detached. ALUs are not permitted in duplexes or townhomes. There are also standards related to owner occupancy, external entrances, parking, curb cuts, etc. Permits must be renewed after an initial two-year period.
Fairfax’s barriers to building ALUs are far more restrictive than nearby municipalities. In Alexandria, Arling-ton, and Loudoun, administrative approval is allowed for detached ALUs, there is no minimum lot size, occupancy by more than two people is allowed, and no permit renewal is required. Alexandria and Loudoun also allow ALUs in duplexes and townhomes.
Presenters said that the county is committed to streamlining the process, but one attendee with experience designing ALUs noted that current recommendations do not go far enough. For example, Planning suggests removing the renewal requirement for permits, or revising those renewals to be every five years, despite no other nearby jurisdiction requiring permit renewals.
Local architect Ileana Schinder, who designs ALUs, says that the current system does not appear designed to encourage ALU adoption. The minimum two-acre property requirement excludes almost all of Mantua. What-ever the county decides, Schinder recommends having clear zoning and building rules, and avoiding confusing occupancy rules, since terms “such as ‘family’, ‘caretaker’ or ‘tenant’ are not practical to regulate.”
The Department of Planning and Development plans follow-up community meetings throughout early 2026, and draft text to revise rules will be presented to the Board of Supervisors this summer.