Design. Build. Live more at Home.

ADU guides

Plain answers to the questions that decide whether an accessory dwelling works on your property: what you could build, what might stop you, and what each route actually involves. Every claim about the rules cites the section of the ordinance it came from, with the date we last checked it.

What you might build

The four routes, and what each one is actually like where you live.

  • Building a separate ADU in your backyard

    Where you live decides this more than anything about your property. A detached unit is allowed by right in Alexandria, allowed in Arlington and Loudoun, and in Fairfax needs a special permit and a lot of at least two acres — which rules it out for most people there. It is also the most expensive route per square foot, because everything has to be built and every service run to it.

    5 min read

  • Turning a garage into an ADU

    Often the cheapest way to get a separate-feeling space, because the shell already exists. The two things that decide whether it works are whether your jurisdiction lets a detached garage hold a dwelling at all, and what happens to the parking you are removing.

    4 min read

  • Turning a basement into an ADU

    Usually the cheapest and quickest route, and in Fairfax it is effectively the only one available on a normal lot. The space and the services are already there. What you are buying is a compliant exit, enough ceiling height, and keeping the water out.

    4 min read

  • Adding an ADU onto your house

    A middle path: cheaper per square foot than a separate building because it shares walls and services, but more freedom than working inside the footprint you already have. The constraint is that it has to work with the house you own — its structure, its roofline, and where it sits on the lot.

    4 min read

Rules and obstacles

The things that decide whether it is allowed at all.

  • Can your HOA stop you building an ADU?

    Yes, and the new state law does not change that. Virginia’s 2027 ADU law expressly does not override recorded covenants, so an association can prohibit a second dwelling however permissive your county is. That makes your covenants the first thing to check, not the last — and often the only thing that actually decides the answer.

    5 min read

  • When does a backyard building count as a home?

    When it has a kitchen, a bathroom and somewhere to sleep. Those three things together are what make it a dwelling in the eyes of the law, with everything that follows — permits, size limits, and in most of Northern Virginia, waiting. Leave any one of them out and you are building an accessory structure instead: simpler, cheaper, quicker, and available now.

    4 min read

Rules differ by jurisdiction, so a guide tells you what to look for and the county pages tell you what your own county says. To get both applied to your address, see what you can build.