Fairfax County ADU Zoning 2026: What Aging Parents Need to Know

Fairfax families looking at a backyard cottage or a basement apartment for an aging parent keep running into two different sets of rules. Virginia passed a statewide accessory dwelling unit law that takes effect July 1, 2027, but it exempts localities that already had their own ordinance before January 1, 2026. Fairfax County had one, so the state law does not apply here. In Fairfax, the county's own accessory living unit (ALU) rules are the ones that count.

Those county rules are being rewritten. The community feedback period closed on September 28, 2026, and the proposal now goes to public hearings: the Planning Commission on Thursday, October 29, 2026 at 7:30 p.m., and the Board of Supervisors on Tuesday, November 17, 2026 at 4:30 p.m. Dates can change, so check the county's ALU page. Until the Board votes, everything below marked "proposed" is a proposal, not the law.

The Rules Today

Under Fairfax's current Zoning Ordinance, according to the county's ALU community toolkit and staff report:

• Interior ALUs (a basement, an addition, or space over an attached garage) need an administrative permit. They're capped at 800 square feet or 40% of the main house, whichever is less.
• Detached ALUs (a separate cottage) need a special permit with a public hearing, and the lot must be at least two acres. They're capped at 1,200 square feet.
• The owner must live on the property, in the main house or the ALU.
• No more than two people can live in the ALU.
• Permits must be renewed, and the approval must be recorded in the county land records.
• One extra parking space is required for the ALU.

What Fairfax Is Proposing

County staff recommends these changes, which the Planning Commission and Board will consider at the hearings. They are proposed only and could change.

Detached ALUs and Lot Size

• Lots of 36,000 square feet or more: a detached ALU would be allowed by right, with no special permit or public hearing. Building permits and other construction approvals still apply.
• Lots under 36,000 square feet: a detached ALU would need a special permit with a public hearing before the Board of Zoning Appeals. The staff report recommends no minimum lot size for this special permit path. An earlier draft (June 30, 2026) set a 15,000-square-foot minimum, and that minimum remains an alternative option the Planning Commission and Board can choose, with a range from 10,500 square feet to two acres.
• Height: on lots under 36,000 square feet, the general 20-foot limit for freestanding accessory structures would apply, with a taller height possible by special permit.

According to the staff report, about 5% of the county's single-family detached homes sit on lots of two acres or more, and another 9% are on lots between 36,000 square feet and two acres. For most Fairfax homes, a detached ALU would still mean a special permit and a hearing.

Size

The proposed cap for both interior and detached ALUs is 1,200 square feet or 40% of the main house, whichever is less. An interior ALU could also use the entire basement, and the Board of Zoning Appeals could approve a larger size by special permit. (Today's interior cap is 800 square feet, and the basement option applies only to basements that existed as of May 10, 2023. The proposal removes that date limit.)

Other Proposed Changes

• No separate administrative zoning permit for by-right ALUs. Building permits are still required.
• No permit renewal and no land-records recordation.
• No owner-occupancy requirement. The county's FAQ notes this would allow both the main house and the ALU to be rented. An option to require owner occupancy when the ALU is first set up is also on the table.
• Up to three people in an ALU (staff evaluated a range of two to four).
• No extra parking space for the ALU.
• Townhouses and duplexes: ALUs aren't allowed there today. An option for interior ALUs in townhouses and duplexes by special permit is included for the Planning Commission and Board to consider.

What Stays the Same

Only one ALU is allowed per lot, with a maximum of two bedrooms. An ALU is a separate unit with its own cooking and eating facilities. It isn't a separate lot, so it can't be sold apart from the main house. Short-term rentals such as Airbnb aren't allowed on a property with an ALU.

The details are in the county's ALU FAQ (October 2, 2026) and the staff report posted on the ALU page.

Arlington and Alexandria

The Fairfax rewrite doesn't apply in Arlington or Alexandria. Each has its own ordinance. A comparison table in Fairfax's staff report lists both as approving interior and detached units through an administrative process rather than a public hearing, with up to three people in the unit, but size limits and other standards differ. Check with your own county or city before you plan.

Why This Matters for Aging in Place

An ALU can solve the stair problem. Your parent gets single-level living space close to family, while keeping their own door and kitchen. The county staff report itself cites an older couple, or a person with a disability living with a caregiver, as the kind of household the occupancy change is meant to serve.

It's also a big project with permits, and on most lots a public hearing. If a separate unit isn't realistic, modifying the main house so your parent can live on one level, through a first-floor bathroom, a stairlift, or a main-level suite, is often the more practical path. Our contractor directory lists aging-in-place professionals in Northern Virginia who can walk the house with you and help you compare both approaches.

Paying for Accessibility Features

Fairfax's ALU rewrite is about zoning, not funding. Some programs may help with accessibility features inside a home or an ALU, such as a zero-step entry, grab bars, or a roll-in shower, but eligibility varies by program, income, and health. See our guides to Virginia home modification programs and VA home modification grants, or our DMV grants overview.

Public Hearings: October 29 and November 17, 2026

According to the county's ALU page:

• Planning Commission: Thursday, October 29, 2026 at 7:30 p.m.
• Board of Supervisors: Tuesday, November 17, 2026 at 4:30 p.m.

Both hearings are in person in the auditorium at the Government Center (12000 Government Center Parkway). The county says information on how to testify is on the Planning Commission and Board of Supervisors websites. Hearing dates can change, so check the county page before you go.

What to Do Right Now

• Check your lot size. Look up your property in the county's records. At 36,000 square feet or more, a detached ALU would be by right under the proposal. Below that, it would need a special permit and a hearing, and whether very small lots qualify depends on which option the Board adopts. Under today's rules, a detached ALU needs two acres and a special permit.
• Consider an interior ALU. A basement or addition is allowed today with an administrative permit, and the proposal would raise the size cap.
• Get the house walked. A CAPS-certified contractor or an occupational therapist can help you decide whether an ALU or a main-level conversion makes more sense for your parent.
• Follow the hearings. Plan around the rules the Board actually adopts, not the proposal.

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Last reviewed October 12, 2026. This article is general information, not legal advice. Zoning proposals and hearing dates can change; confirm with Fairfax County before you plan or build.