ADU Builder in Arlington, VA

Arlington lots tend to be small, and many of the houses on them are older than most in Northern Virginia. A 1940s Cape Cod in Lyon Park, a brick rambler off Glebe Road, a bungalow a few blocks from the Orange Line. Those are the homes where an accessory dwelling makes the most sense, and also where the rules pinch hardest. DLA Design & Build plans and builds accessory dwellings for Arlington homeowners, from basement apartments to new backyard cottages. We sort out the County's Accessory Dwelling permit before any wall comes down, because in Arlington the zoning approval comes first and the building permit follows it.
Zoning approval first. Then permits. Then a crew that shows up.

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Why Arlington Homeowners Are Building Second Units

Much of Arlington's rental housing is apartments along the Rosslyn-Ballston corridor and down toward National Landing. A basement unit with its own door a short walk from Clarendon offers what a high-rise can't: a yard, a quiet block, a landlord upstairs. That last part matters here. The County requires the owner to live in either the main house or the accessory dwelling, so the Arlington model is usually live upstairs, rent downstairs.
Family is the other driver. Owners who bought decades ago now have a parent who needs to be close, or a grown kid who can't touch local rents. We start with who will live in the unit, because a tenant, a parent with a walker and a college grad need different doors, kitchens and bathrooms (the in-law suite section below explains the family options).
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ADU Types We Build in Arlington, VA

Every type below can be built in Arlington, just not on every lot. Here is how the County's rules and the local housing stock shape each one.

01Detached ADU

Detached ADUs in Arlington

A new backyard cottage is legal in Arlington, but the lot has to earn it. A detached building put up after May 18, 2019 can be no taller than one and a half stories or 25 feet, whichever is less, must sit 25 feet back from the street and 8 feet from the house, and needs 5 feet from side and rear lines on an interior lot. Its footprint stops at 560 square feet in R-5 and R-6 and 650 in the other districts. On a narrow lot in Westover or Lyon Village, that often leaves one spot in the back corner, and a mature oak can take that away. We start with a survey and a walk around the trees, then tell you plainly whether a cottage fits or a basement unit is the smarter build.

02Attached ADU

Attached ADUs in Arlington Homes

An attached unit lives inside or against the house but runs on its own: a separate entrance, its own kitchen and bath, and a fire-rated wall or floor between it and your living space. Arlington sizes it by the main house. On a home of 1,000 square feet or more, the unit can be up to 35 percent of the combined floor area, topping out at 750 square feet. Smaller homes get 45 percent, capped at 500. For a brick colonial with an unused wing or a large side room, carving a unit out of existing space is often quieter and faster than building new. We put the entrance on the side or rear so the house still reads as one home from the street.

03Basement ADU

Basement Apartments in Arlington

This is where most Arlington accessory dwellings end up, and the rules explain why. A unit that sits wholly inside the basement has no County size cap, so the entire lower level can become the apartment. What limits you is the basement itself. Many pre-war and post-war Arlington homes have ceilings that barely clear seven feet, stairs that land in the middle of the space, and foundations that were never waterproofed. We check ceiling height, plan egress windows or a walkout door, and deal with water before anything is framed. On the hilly streets of Donaldson Run, a walkout wall can make the unit feel like a garden apartment. Our basement remodeling crews handle the finish work.

04Garage Conversion

Garage Conversions in Arlington

Plenty of older Arlington lots have a detached garage at the end of the driveway, and the County gives those buildings some room. For an accessory building built before May 18, 2019, the County sets no specific height, footprint or setback limits, but any alterations must be confined to the interior. That can make an old garage the only detached option on a lot where a new cottage wouldn't meet setbacks. Three cautions. The interior-only rule means we confirm with Zoning early how the garage door opening will be handled. The County requires you to keep your existing off-street parking, so we work out where the car goes before the garage stops being a garage. And many of these garages sit on thin slabs with little or no footing, so we open up the structure early to see whether it's worth saving.

05In-Law Suite

In-Law Suites in Arlington

An in-law suite and a legal accessory dwelling are not always the same thing. In Arlington, an accessory dwelling is a complete independent unit with its own kitchen and bath, and it needs the Accessory Dwelling permit, the recorded covenants and the occupancy limits that come with it. A bedroom, bath and sitting room for a parent that shares the family kitchen is not an independent unit, so it's permitted as part of your house. Families choose based on how independent the parent wants to be and whether the space might be rented later. Whichever path you pick, we plan for aging in place: a zero-step entry, a curbless shower, wider doors and blocking in the walls for grab bars.

06Guest House

Guest Houses in Arlington

Arlington's zoning ordinance treats a guest house as its own use, separate from an accessory dwelling. It is allowed only with a single-family detached home, is meant for temporary guests of the people living there, can't have kitchen facilities, and can't be rented or used as a separate dwelling. The ordinance defines a guest as someone invited to stay without paying, for no more than 30 days in a year. It still has to meet the regular rules for the zoning district. That makes a guest house a good fit for visiting family, a home office or a studio at the back of the yard, but not for a tenant. If you might want rental income or a permanent resident later, permit it as an accessory dwelling from the start.

07Above-Garage ADU

Apartments Over a Garage in Arlington

A carriage house, with parking below and a unit above, is possible in Arlington, but the height rule is tight. A detached building constructed after May 18, 2019 is limited to one and a half stories or 25 feet, whichever is less, so the upstairs unit lives partly under the roof slope, and dormers do a lot of work. The County also bars exterior stairs above the first floor on street-facing sides, so the stair goes inside or around back. The building's footprint counts against the 560 or 650 square foot cap, which means the garage bays, the stair and the unit above all share one small rectangle. Adding a floor to an older garage goes beyond the interior-only conversion the County allows for pre-2019 buildings, so we plan it under the new-building limits, and it usually means new footings, because most old garage slabs were never meant to carry a second story.

08ADU Addition

ADU Additions in Arlington

When the basement is already finished or too shallow, new footprint can create the unit: a rear wing, a side addition or a second story over part of the house. An addition that holds the accessory dwelling has to meet the main house's setbacks and lot coverage limits rather than the detached-building rules, and the unit still counts against the 35 or 45 percent share of combined floor area. On a Cape Cod, a second-story addition can move the family upstairs and free the original first floor for the unit. We match the exterior to the original house, and our Arlington home additions team handles the structural side through the same County review.

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How Arlington County Regulates Accessory Dwellings

Arlington is a county with no incorporated towns, so every address runs through one government. Accessory dwellings start with an Accessory Dwelling permit from the Zoning Division, submitted through Permit Arlington. Staff quote roughly thirty days for zoning review. Once the Zoning Administrator approves, you record a Declaration of Covenants in the Circuit Court's land records, and only then can the building permit issue. The house must be a single-family detached home in one of the eligible residential districts (R-20, R-10, R-8, R-6, R-5, R-10T, R-15-30T or R-2-7), with no existing accessory dwelling.
The size limits depend on the house. If the main dwelling has at least 1,000 square feet, the unit can be up to 35 percent of the combined floor area, capped at 750 square feet. Under 1,000 square feet, it's 45 percent, capped at 500. A unit entirely inside a basement has no set size limit. No more than three people may live in the accessory dwelling, and the owner has to live on the property in one of the two units.

Detached units in buildings built after May 18, 2019 carry their own rules: one and a half stories or 25 feet tall at most, whichever is less, 25 feet back from the street, 8 feet from the main house, and 5 feet from side and rear lines on interior lots (corner lots need 10 feet at the rear). The footprint tops out at 560 square feet in R-5 and R-6 and 650 elsewhere. Homes in a local historic district such as Maywood also need a Certificate of Appropriateness for exterior work, which goes before the Historical Affairs and Landmark Review Board.
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Frequently Asked Questions About ADUs in Arlington, VA

No, and people mix them up constantly. The Expanded Housing Option, adopted in 2023, lets certain lots be developed with two to six units: duplexes, townhouses or small multifamily buildings. An accessory dwelling is one extra unit that stays subordinate to your single-family house. The EHO has been tied up in court. The Court of Appeals of Virginia reversed the Circuit Court judgment that struck it down, the County resumed taking applications in October 2025, and the Supreme Court of Virginia agreed in May 2026 to hear a procedural appeal. For a basement apartment or backyard cottage, you are under the accessory dwelling rules, not the EHO.

Yes, as long as you live on the property. The County requires the owner to use either the main house or the accessory dwelling as a primary residence, and caps the unit at three occupants. If you plan to move out someday and rent both, the rule changes the math: with no owner on site, the property is limited to one family. We ask about your five- and ten-year plans at the first meeting, because the answer can change whether we build a unit or a guest suite.

If the whole unit sits inside the basement, the County sets no specific size cap. That is one reason basement units are so common here. The practical limits come from the house itself: ceiling height, where egress windows can go, how the stairs land, and whether the foundation stays dry after a hard rain. Plenty of 1940s and 1950s Arlington basements were built with low ceilings and minimal waterproofing, so we check those before promising a floor plan. The basement apartment section above covers the build side.

Not under the accessory dwelling rules. Arlington limits accessory dwellings to lots with a single-family detached house in the eligible residential districts, and the lot can't already have one. Owners of townhouses and semi-detached homes sometimes ask about Missing Middle instead, but that program governs building new multi-unit housing, not adding a unit behind an existing attached home. If you own a townhouse and want space for family, a finished lower level or a suite that stays part of your home is the realistic route, and we can walk through what that looks like.

Not necessarily. Arlington's accessory dwelling rules require you to keep the off-street spaces you already have, so paving over the driveway for a patio is off the table. A lot with no off-street parking must either add a space or submit a parking study through the Department of Environmental Services showing the block has on-street capacity. On older streets near Metro that study can go either way, so we walk the block at different times of day before design work gets expensive.

You file an Affidavit of Compliance, pass final inspections and receive a Certificate of Occupancy before anyone moves in. The recorded covenants stay with the property, and the Zoning Administrator can inspect the unit annually to confirm it still meets the conditions. None of this is a burden if the unit matches the approved plans. It does mean the paperwork matters as much as the framing, and a buyer's agent may ask for it someday.

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How We Run an Arlington ADU Project

We start at your house with the plat, a tape measure and a flashlight for the basement. Before anyone draws a floor plan, we check your zoning district, the main house's floor area, existing parking and, for a detached unit, whether the footprint and setbacks leave a buildable spot. That visit usually settles which unit type is realistic.
From there we design, prepare the Accessory Dwelling permit application, handle the covenant recording and pull the building and trade permits. Our crews build the unit and schedule inspections. You can see the kind of additions and remodels we build on our work page.

What You End Up With

A legal, permitted second home on your lot with its own kitchen, bath and door, recorded properly with the County, so it adds value when you sell instead of raising questions at the home inspection.
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ADU Builder in Nearby Communities

We plan and build ADUs across Northern Virginia. See local details for nearby areas.

Talk to an Arlington ADU Builder

Call (703) 743-7777 or send us a note with your address. We'll look up the zoning before we meet.
Bring your plat if you have it. If not, we can work from County records.

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