ADU Builder in Alexandria, VA

Alexandria has allowed accessory dwelling units citywide since City Council approved its ADU policy in January 2021, and the rules are friendlier than most people expect. Townhouses qualify. No extra parking space is required. A backyard unit can sit a foot off the rear lot line. DLA Design & Build designs and builds these units for Alexandria homeowners: English basements under Del Ray bungalows, cottages behind Rosemont foursquares, garage conversions off the alleys. We draw to the City's setback and height limits from the first sketch, and in the historic districts we plan for the Board of Architectural Review before we plan the kitchen.
One unit, built right, on a lot that looked too small for it.

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Why Alexandria Is Good Ground for an ADU

Plenty of older Alexandria lots are narrow and deep, with a detached garage or shed at the back and sometimes an alley behind that. That shape suits a backyard unit. It keeps the new building away from the street, gives a tenant or family member a separate path in, and leaves the front of the house alone. The City's setbacks for these units are measured in single feet, not tens of feet, which is what makes those lots workable.
Demand is steady. Alexandria sits close to the Pentagon, National Landing and downtown DC, with Blue and Yellow line stations, and small rentals in walkable neighborhoods are hard to find. Families use the units too, for a parent who wants to stay near grandkids in Beverley Hills or a son finishing graduate school. The in-law suite section below explains how a family unit differs from a rental.
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ADU Types We Build in Alexandria, VA

The City's rules favor some unit types over others. Here is how each one works on an Alexandria lot, including the ones that are harder than they look.

01Detached ADU

Detached ADUs in Alexandria

Alexandria is one of the easier places in Northern Virginia to put a cottage in the backyard. The building can sit in the required side and rear yards, as close as one foot from the lot line if no wall with windows or doors faces it, and three feet if one does. Height is capped at 20 feet or the height of your house, whichever is lower, and the parts above 13.5 feet carry their own setbacks. The first floor can be the larger of one-third of the house's first floor or 350 square feet on lots of 2,500 square feet or less, 500 on larger lots. Behind a Del Ray bungalow with an alley at the back, that is often enough for a one-bedroom unit with its own path to the street.

02Attached ADU

Attached ADUs in Alexandria

Inside the City, an accessory dwelling within the main house can be up to one-third of the home's gross floor area. Alexandria allows accessory dwellings with townhouses and two-unit homes as well as detached houses, and for a West End townhouse or a duplex near Braddock Road, an attached unit is often the only realistic choice. The work is in the separation: a rated wall or floor between the units, sound control so two households can keep different hours, and an entrance that doesn't lead a tenant through your living room. The City spells out what an ADU kitchen must include: a sink, a cooking appliance, a prep counter, storage cabinets and a refrigerator. We plan all five from the first drawing.

03Basement ADU

Basement Apartments in Alexandria

The English basement, a lower-level unit with its own door a few steps below grade, is a familiar form in Alexandria. Under the current rules, a unit inside the house counts toward the one-third of gross floor area limit, so a big basement under a modest house may need a partition to stay within it. The physical questions matter just as much: ceiling height, egress windows that meet code, drainage that keeps water out during a summer storm, and where the stair lands. Some homes in Rosemont and Seminary Hill sit on sloping lots with part of the basement above grade, which makes daylight and a separate entrance easier. Our basement remodeling team handles the finish work.

04Garage Conversion

Garage Conversions in Alexandria

Many older lots in Del Ray, Rosemont and the historic districts have a detached garage or carriage building at the back, sometimes close to the property line. If that building already meets the ADU rules for size, height and setbacks, it converts like any other detached unit. If it doesn't, the City offers a path: a detached accessory building that existed before February 20, 2021 can be expanded, altered or rebuilt for an accessory dwelling by special exception from the Board of Zoning Appeals, as long as the work doesn't make its nonconformity worse. The ADU needs no off-street parking, which helps when the garage was the only covered space. We check the slab, framing and drainage before recommending conversion over replacement.

05In-Law Suite

In-Law Suites in Alexandria

Plenty of Alexandria families want a parent close without creating a rental. The line between an in-law suite and a legal accessory dwelling comes down to the kitchen and independence. The City treats an accessory dwelling as its own dwelling unit, subordinate to the main home, and its kitchen must have a sink, a cooking appliance, a prep counter, storage cabinets and a refrigerator. A suite that shares the family kitchen is a renovation or addition to your house, not an ADU. Many owners in Seminary Hill and Beverley Hills build the full unit anyway, because it keeps options open and the current ordinance has no owner-occupancy requirement. Either way, we design for aging in place: step-free entry, a curbless shower and doorways wide enough for a walker.

06Guest House

Guest Houses in Alexandria

The City lists guest houses separately from accessory dwellings. A guest house is allowed as an accessory to a single-unit home when it is used by temporary guests or people who live in the main house, has no kitchen facilities, and is not rented or used as a separate dwelling. Here is the practical catch. The ADU section lets a unit sit in the required side and rear yards with small setbacks. An ordinary accessory building generally can't go in those required yards. So a pool house or studio built as a guest house may have to sit farther from the lot lines than a full ADU would. On a narrow lot, permitting the building as an ADU can actually give you more room to place it.

07Above-Garage ADU

Apartments Over a Garage in Alexandria

A garage with an apartment above is the hardest ADU type to fit under Alexandria's rules. The whole building is capped at 20 feet or the height of your house, whichever is lower, and any part above 16 feet must be at least five feet from side and rear lines. Two full stories plus a pitched roof rarely fit in 20 feet, so these designs lean on low-slope roofs, a garage with a modest ceiling and careful stair placement. The first-floor size limit applies to the garage level too. Where it works, usually on a deeper lot with an alley, a carriage house puts the car below and a compact studio above. Where it doesn't, a one-story cottage beside a parking pad is usually the better answer.

08ADU Addition

ADU Additions in Alexandria

An addition that holds the unit is part of the main house, so it follows the zone's normal setback and floor area rules rather than the special yard allowances for detached ADU buildings, and the unit inside still has to stay within one-third of the house's gross floor area. In Old Town and Parker-Gray, anything visible from a public way also needs a Certificate of Appropriateness, so the addition's roofline, windows and materials go through historic review. On larger lots in Beverley Hills or Seminary Hill, a side wing or rear addition can create a unit with ground-level access and no stairs, which suits a parent or a tenant with a bike. Our Alexandria home additions team handles the structural side.

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City of Alexandria ADU Rules, and When They Don't Apply

The City of Alexandria is an independent city, so City zoning applies, administered by the Department of Planning and Zoning. The rules live in Section 7-203 of the Zoning Ordinance. One accessory dwelling is allowed per lot, attached to a single-unit, two-unit or townhouse dwelling. A unit inside the main house can be up to one-third of the home's gross floor area. A detached unit's first floor can be the larger of one-third of the main house's first floor or 350 square feet (lots of 2,500 square feet or less) or 500 square feet (larger lots). Its height can't exceed 20 feet or the height of the house, whichever is lower.
Setbacks for a detached unit start at one foot from side and rear lines, or three feet if a wall with windows or doors faces the nearest line. Portions between 13.5 and 16 feet tall need at least 2.5 feet, and portions above 16 feet need five. No off-street parking is required. The ADU and main house have to stay under common ownership. Inside the Old and Historic Alexandria and Parker-Gray districts, new construction and exterior changes visible from a public way need a Certificate of Appropriateness from the Board of Architectural Review or preservation staff.

Here is what trips people up: many houses with an Alexandria mailing address are not in the City at all. Mount Vernon, Belle Haven, Franconia, Hybla Valley and much of the Route 1 corridor are unincorporated Fairfax County, and Fairfax County's accessory living unit rules apply there instead. Those are far stricter on detached units, which currently need a special permit and a lot of at least two acres. Fairfax has a rewrite under study in 2026, but it has not been adopted. Your real estate tax bill tells you which government you pay, and that is the one that governs.
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Frequently Asked Questions About ADUs in Alexandria, VA

Check who sends your real estate tax bill. If it comes from the City of Alexandria, City zoning applies. If it comes from Fairfax County, you are in unincorporated Fairfax County even though the Post Office says Alexandria. The difference is not small. Inside the City, a backyard cottage can be approved on a modest lot. In Fairfax County, an interior accessory living unit goes through an administrative permit with its own size and parking rules, and a detached one requires a special permit and at least two acres under the current ordinance. We confirm the jurisdiction before anything else.

Yes, which is unusual. Arlington and Fairfax County limit their units to single-family detached homes, while Alexandria allows them with townhouses and two-unit dwellings too. Whether one physically fits is another question. Townhouse rear yards are often short, and the height and setback limits still apply. On many townhouse lots the better answer is a lower-level unit with its own entrance, and we'll tell you honestly which one your lot supports.

The current text of Section 7-203 requires that the ADU and the main house stay under common ownership, so you cannot sell the unit off separately. It does not include an owner-occupancy requirement. The City's short-term rental rules add one limit: you cannot list both the main house and the ADU as short-term rentals at the same time. Rules change, so we confirm the current language with Planning and Zoning when your application goes in.

That triggers a rule many owners miss. Outside the Old and Historic Alexandria and Parker-Gray districts, if the house next door has windows or doors within three feet of the shared line, and their sills or thresholds sit lower than your proposed building, the building holding your ADU must stay at least five feet from the line along the width of those openings and five feet past them in each direction. On a narrow Del Ray or Rosemont lot, that can shift a cottage over or change its shape. We note the neighbor's openings on the survey before we design.

It can be, but the Board of Architectural Review becomes part of the design team. Any new building or exterior change visible from a public way in the Old and Historic Alexandria or Parker-Gray districts needs a Certificate of Appropriateness. We check what can be seen from the street and alley before design starts, design the exterior to fit the block from the start, choose materials the Board is used to approving, and build time for the hearing into the schedule.

No. Alexandria exempts accessory dwellings from off-street parking. That matters on Del Ray and Rosemont streets where many houses never had a driveway, and it means a small lot doesn't lose yard space to a parking pad it would otherwise need. If your lot does have a garage or pad, converting it is a design choice for you, not a parking problem for the City. The garage conversion section above covers what that build involves.

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From Survey to Move-In

We start with a survey and your tax record to confirm the jurisdiction. Then we test floor area, height and setbacks against your lot, flag any historic review, and show you where a unit fits. For backyard units we also plan foundations, utility runs and how materials reach a tight rear yard.
Once the design is set, we prepare the zoning and building submissions, take the project to the BAR if needed, and build with our own crews. Projects that also expand the main house go through the same City review.

The Result

A permitted, code-compliant unit with its own kitchen, bath and entrance, sized to the City's limits and designed to look like it belongs on the block.
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ADU Builder in Nearby Communities

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

Start Your Alexandria ADU

Call (703) 743-7777 and tell us your address. We'll confirm City or County before we talk layouts.
If you're in Old Town or Parker-Gray, mention it up front.

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