Start building your dream ADU.
You likely don't have to wait until the Virginia ADU Law (SB 531) goes into effect on July 1, 2027 to start building your dream ADU! We're a licensed Virginia general contractor based in Arlington, and we read these ordinances for a living. Start with our free tool to find out what your lot allows. Then, if you're ready to build it, we're the ones who can.
See what you can buildAbout two minutes. No email needed to see your result.
Start with your county
Every rule on these pages links to the section of the ordinance it comes from, so you can read it yourself.
Alexandria CityAlexandria is the most permissive jurisdiction in Northern Virginia for this. A separate building in the backyard is allowed outright, it can sit as close as a foot from your side or rear line, no extra parking is required, and you do not have to live on the property. You do not have to wait for July 2027. Check first that you are actually in the City — a great many "Alexandria" addresses are in Fairfax County, which is stricter.
Arlington CountyArlington already allows a second dwelling on a single-family lot, including a detached one in a backyard building. You do not have to wait for July 2027. The main limits are size, a 25-foot distance from the street, and that you live in one of the two units.
Fairfax CountyRight now Fairfax only lets you put a second living space inside your existing house. A separate backyard cottage needs a special permit and a lot of at least two acres. That changes on July 1, 2027, when state law requires Fairfax to allow detached units as a permitted accessory use. If your property is in an HOA, the state law does not override your covenants.
Loudoun CountyLoudoun already allows a second dwelling on a residential lot, detached or inside the house, and the size limits are the most generous in Northern Virginia — up to 2,500 sq ft on rural land. You do not have to wait for July 2027. How big yours can be depends on which zoning district your lot sits in.
Why this site is different from the other ADU pages you've read
Most Northern Virginia ADU content is a summary of a summary, and the errors get copied along with everything else. Every rule on our website comes from the ordinance itself, cited to the section, with the date we last read it. We know these ordinances. We also know how to build a beautiful ADU.
What does this mean for your lot?
Three questions. We’ll check the rules against your situation and tell you what you’re actually looking at — including if the answer is no.