Virginia ADU law
By Cheryl Spangler, Class A RBC licensed builder · September 2026 · 8 minute read
For decades, whether you could build a small home in your own backyard in Virginia depended entirely on which county you happened to live in. In some places it meant a special use permit, a public hearing, and neighbors who did not object. In others it was effectively impossible.
That ends. Senate Bill 531 was signed into law in April 2026 and takes effect July 1, 2027. It is the most significant change to Virginia residential zoning in a generation, and most homeowners have not heard of it.
Here is what it does, what it does not do, and what to do with the months in between.
Zoning ordinances for single-family residential districts are now deemed to include accessory dwelling units as a permitted accessory use, and localities cannot impose requirements beyond those the statute specifically allows.
That phrase, permitted accessory use, is the whole ballgame. It means an ADU becomes something you have a right to build, rather than something you apply for permission to build and hope a board approves.
You still need an ADU permit from your locality, but the fee is capped at $500. That cap covers the ADU permit itself; inspection, site and building permit fees still apply on top. If your application demonstrates compliance with the statute and applicable local codes, the locality must issue the permit.
The law is a floor, not a blank check. Localities may still require a minimum lease term of 30 consecutive days, replacement parking if the ADU eliminates the primary home’s required spaces, dedicated parking for the ADU itself, and compliance with building codes, water, sewer, septic, emergency access, flood zone and stormwater requirements.
They may also set floor area limits, though not below 350 square feet on lots under 2,500 square feet or 500 square feet on larger lots. They may require that the owner occupy either the ADU or the primary dwelling, but not both, and only at the time of application. They may require the ADU sit within 500 feet of the primary dwelling, prohibit an ADU on a lot that already has more than one dwelling, and prohibit selling or subdividing the ADU away from the main house.
Historic districts, architectural review corridors and Air Installations Compatible Use Zone restrictions all survive as well.
This is where the real change lives. Localities cannot impose rear or side setbacks greater than what is required for the primary dwelling or for accessory structures, whichever is less. They cannot apply height, setback, lot size, lot coverage or building frontage rules more restrictive than those applied to single-family homes in the same zone. They cannot require a restrictive covenant. They cannot demand public street improvements as a condition of approval, except to repair a street their own construction disturbed.
And the one that matters most to families: localities can no longer require consanguinity or affinity between the occupants of the ADU and the main house.
The family-only rule is gone. Counties spent years permitting backyard cottages on the condition that only a relative could live there. That condition is no longer enforceable.
Read the last line of the statute carefully, because it undoes the headline for a lot of people. The section does not apply to a locality that adopted an ADU ordinance prior to January 1, 2026.
Alexandria, Arlington County and Fairfax County all had ADU ordinances on the books before that date, which means they may not be automatically subject to SB 531. Fairfax calls them Accessory Living Units and has historically required a two-acre minimum lot for detached units. Arlington calls them Accessory Dwellings and previously prohibited detached ones outright. Loudoun County, Prince William County and most other Northern Virginia jurisdictions appear to have had no prior ADU ordinance, which would put them under the state framework when it takes effect. That is the likely reading, not a settled one, and the reason why is worth understanding.
So the answer to “can I build an ADU” still depends on your county. It just depends on it for a different reason than before.
Most homeowners do not want a basement apartment. They want a cottage in the backyard. So the first question is always the same: does this law actually let me build a separate building?
Under SB 531, yes. The statute defines an accessory dwelling unit as an attached or detached dwelling unit on a residential lot, and its building-code provision spells out requirements for an ADU that is detached. A locality covered by the law cannot permit attached units and refuse detached ones after July 1, 2027.
Today is a different story. Prince William County’s zoning ordinance states that no accessory structure in an agricultural or residential district may be used as a dwelling, dwelling unit or place of residence. What the county permits instead is a secondary food preparation area inside the main house. Not a separate dwelling. Fairfax County approves interior conversions administratively, but detached units on most lots still require a Special Permit.
So the practical answer for the next several months is that a detached cottage is difficult or impossible in much of Northern Virginia, and the law that changes it does not take effect yet.
The exemption turns on whether a locality adopted an ADU ordinance before January 1, 2026. The statute does not define what counts as one.
Fairfax is the clear case. It has a real Accessory Living Unit ordinance that predates the cutoff, so it is very likely exempt, and its own rules continue to govern.
Prince William is the harder one. A county that prohibited accessory dwellings did not adopt an ADU ordinance. It adopted a ban. Whether a prohibition qualifies as an ordinance for the purpose of this exemption has not been tested, and reasonable lawyers will read it differently.
There is also a naming trap worth knowing about. Prince William has an AfDU Ordinance, for Affordable Dwelling Units, adopted under an entirely different section of state code. Same-sounding acronym, unrelated subject. It is easy to see that and conclude the county has an ADU ordinance and is therefore exempt. It is not the same thing.
The honest position, from someone who builds these: no one can tell you today exactly what your county will permit in July 2027, because most counties have not decided. Several are actively rewriting their ordinances right now. What you can do is find out what your lot can physically support, which does not depend on any of this.
The statute explicitly preserves private covenants: recorded declarations, condominium instruments, common interest community declarations and property owners’ association documents.
If your neighborhood’s covenants prohibit a second structure or ban rentals, SB 531 does nothing for you. The legislature preempted your county and left your HOA entirely alone. Before you spend a dollar on design, read your declaration.
Here is the part that will surprise people in 2027. Making an ADU legal does not make it fast.
On a small-footprint build, construction is roughly thirty days. Everything before it, site evaluation, septic or sewer capacity, engineering, stormwater, financing, plan review and permit issuance, is the other sixty. SB 531 removed the discretionary hearing. It did not touch septic capacity, engineering, or the appraisal problem that makes these projects hard to finance.
The bottleneck moved. The question is no longer whether the county will let you. It is whether your lot can physically carry a second dwelling, and whether anyone will lend against it.
Find out whether your locality is exempt. If you are in Fairfax, Arlington or Alexandria, you are operating under local rules. Confirm current requirements with your planning department.
Read your HOA covenants first. Cheapest step, and the one most likely to end the project.
Get a soils and septic evaluation. If you are on septic, capacity for a second dwelling is the most common reason an otherwise perfect lot fails. Find out now, not in 2028.
Measure your setbacks honestly. The law caps what your county can demand, but your lot geometry is still your lot geometry.
Start the financing conversation early. Small detached homes and ADUs rarely have clean comparable sales, and appraisals come back short. Lenders are adapting slowly.
Do not wait until July 2027 to begin. Localities may adopt compliant ADU ordinances before the effective date, and permits already approved are undisturbed. Design, site work and financing can all happen ahead of a permit.
ADU Virginia maintains accessory dwelling unit regulations locality by locality across the Commonwealth.
Cheryl Spangler is a Class A RBC licensed builder and owner of ESC Homes, which builds small-footprint homes and accessory dwelling units in Northern Virginia. She is also a licensed real estate broker and speaks on ADU policy, permitting and small-home construction.
General information, not legal advice. Verify current requirements with your locality’s planning department before making decisions. Statutory text: Code of Virginia § 15.2-2292.4 (2026, c. 895).