ADU Builder in Falls Church, VA

The City of Falls Church wrote its accessory dwelling rules recently, adopting the current standards in April 2025, and they are some of the more generous in the inner suburbs. A unit can reach 1,000 square feet on a larger house, no parking space is required, and a detached cottage can tie into the main house's water and sewer lines. DLA Design & Build designs and builds these units, from backyard cottages behind post-war ramblers to lower-level apartments under older brick colonials. We also know that many people with a Falls Church mailing address don't live in the City at all, and we sort that out first.
Newer rules, a small city, and a builder who reads the code before drawing.

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Why an ADU Makes Sense in Falls Church

Falls Church is small, walkable and expensive to move into. The West Falls Church and East Falls Church Metro stations bracket the City, Broad Street has restaurants and shops within walking distance of many homes, and the schools draw families. Land is the scarce part. An accessory dwelling adds a home without adding a lot.
Some owners build for a parent who wants to stay close. Some build for long-term rental income. Others build for family now and keep the option to rent later. The City's rules let a unit hold up to four people, which gives more room to work with than neighboring jurisdictions.
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ADU Types We Build in Falls Church, VA

These sections cover properties inside the City of Falls Church. If your tax bill comes from Fairfax County or Arlington, different rules apply.

01Detached ADU

Detached ADUs in Falls Church

Falls Church pairs generous size limits with fairly strict setbacks for backyard units. A one-story cottage up to 15 feet tall needs eight feet from side and rear lines, and the Board of Zoning Appeals can reduce that to five by special use permit. Anything taller needs ten. The unit must be at least five feet from the house, can't sit in the front yard or closer to the street than the house, and can't exceed 20 feet, one and a half stories or the main house's height. Lot coverage limits apply on top of that. On corner lots the numbers change again. On the deeper lots found in parts of the City, a one-story, one-bedroom cottage usually fits once those lines are drawn.

02Attached ADU

Attached ADUs in Falls Church

An attached or interior accessory dwelling in Falls Church follows the same setbacks as the main house, which makes it the easiest type to site on a narrow lot. Size is where the City is generous, with caps high enough for a real one-bedroom with a separate living room (the FAQ below gives the numbers). The work is in the separation that lets two households share a roof: a rated wall or floor, an entrance on the side or rear, and sound control between bedrooms. Up to four people can live in the unit, one more than neighboring Arlington allows, which makes an attached unit practical for a small family rather than a single tenant.

03Basement ADU

Basement Apartments in Falls Church

The City's basement rule is simple: an accessory dwelling wholly within a basement can use the entire basement, regardless of the size caps that apply to other units. For the brick ramblers and split-levels built across Falls Church after World War II, that can turn an underused rec room into the largest possible unit without adding any footprint. The limits are physical. We check ceiling height, plan egress windows or a walkout door, fix grading and drainage, and route plumbing so the kitchen and bath drain properly, which sometimes means an ejector pump. Our basement remodeling crews handle the finish work.

04Garage Conversion

Garage Conversions in Falls Church

An existing detached garage can become a unit two ways. If it meets today's accessory dwelling standards for setbacks, height and size, it converts like any new detached unit. If it doesn't, and it was built before January 1, 2024, the Board of Zoning Appeals can grant a special use permit allowing it to be occupied as an accessory dwelling anyway. The catch is that such a structure may not be extended, so the unit has to fit inside the walls you already have. Old one-car garages are small, which usually means a studio. An attached garage is a different case: converting it creates an interior unit that follows the main house's setbacks. No parking space is required for the unit, but we'll plan where your cars go before the door comes off.

05In-Law Suite

In-Law Suites in Falls Church

The City defines an accessory dwelling as a complete independent unit with a kitchen and bathroom, on the same lot and under the same ownership as a one-family home. A suite for a parent that shares the main kitchen doesn't meet that definition, so it's permitted as part of the house. Add a full kitchen so the space works as an independent unit, and it becomes an accessory dwelling, with its own building permit, certificate of occupancy and owner-residence rule. For many families the full unit is the better long-term choice because it can shift to a long-term rental later. Whichever you choose, we design for aging in place: no-step entry, curbless shower, lever handles and wider doors.

06Guest House

Guest Houses in Falls Church

Falls Church's zoning code doesn't have a separate guest house category the way Arlington and Alexandria do. A detached building without a kitchen, used as a studio, office, pool house or place for visitors to sleep, is handled as an accessory building. In the R-1A district, buildings containing only accessory uses are limited to 12 feet in height and need three feet from side and rear lines. Add a kitchen and bath and it becomes a detached accessory dwelling, with the larger setbacks and the 20-foot height limit that go with it. So the choice has real design consequences: a low studio can sit near the back line, while a rentable cottage needs more room. We map both options on your plat before you decide.

07Above-Garage ADU

Apartments Over a Garage in Falls Church

A carriage house is possible here, but three rules shape it. Height can't exceed 20 feet, one and a half stories or the height of the main house. Anything taller than 15 feet or one story needs ten feet from side and rear lines. And any upper-story portion with windows that aren't clerestory has to be ten feet from every property line. In practice that means a garage with a half-story unit tucked under the roof, lit by skylights, dormers facing your own yard, or high clerestory windows toward the neighbors. On substandard lots the height limit scales down with lot area, though it doesn't have to drop below 15 feet. We check the lot's status first, because that alone can decide whether a second level works.

08ADU Addition

ADU Additions in Falls Church

Attached accessory dwellings follow the main house's setbacks, so an addition can place a unit where a detached cottage never could. In the R-1A district, that means the house's normal yards (30 feet in front, 15 on each side and 40 in the rear) and a 25 percent cap on lot coverage by buildings. A side wing on a wide lot or a second story over an existing rambler are the usual answers. A second-story addition can move the family upstairs and let the original main level become a step-free unit for a parent. We design the tie-in so the roofline and siding match, and our Falls Church home additions team handles the structural work.

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City of Falls Church Accessory Dwelling Rules

Inside the City limits, accessory dwellings are allowed by right in the R-1A, R-1B and R-M residential districts, and the standards sit in the zoning chapter of the City Code. Size depends on the main house. If the house is over 1,400 square feet, the unit can be up to 1,000 square feet or half the house's gross floor area, whichever is less. If the house is 1,400 square feet or smaller, the cap is 700. A unit entirely inside the basement can use the whole basement. No more than four people may live in the unit, it can't be used as a short-term rental, and the owner must be living on the property as a primary residence when the permit and certificate of occupancy are issued (new construction that builds the house and unit together is the exception).
Detached units have the tightest rules. Height can't exceed the main house, 20 feet or one and a half stories. A unit up to 15 feet or one story sits at least eight feet from side and rear lines (the Board of Zoning Appeals can reduce that to five by special use permit), taller units need ten, and any upper-story wall with regular windows has to be ten feet from every property line. The unit must be at least five feet from the house and can't be in the front yard. Lot coverage limits still apply, and no parking space is required.

Now the address problem. Much of what's called Falls Church is unincorporated Fairfax County: Lake Barcroft, Seven Corners, Pimmit Hills, Idylwood and plenty of streets with a 22042 or 22043 ZIP. There, Fairfax County's accessory living unit rules apply, and a detached unit currently needs a special permit and a two-acre lot. The East Falls Church neighborhood around that Metro station, despite its name, is in Arlington County, which has its own accessory dwelling permit. Check your real estate tax bill to see which government you're under.
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Frequently Asked Questions About ADUs in Falls Church, VA

Only if your property is inside the City of Falls Church. Look at your real estate tax bill. If the City sends it, the City's accessory dwelling standards apply. If Fairfax County sends it, you are under Fairfax County's accessory living unit rules, which allow interior units by administrative permit but limit detached units to lots of two acres or more with a special permit, at least until the County finishes its current review. If Arlington sends it, Arlington's accessory dwelling permit governs. We check this before the first sketch, because it changes what's buildable.

Inside the City, the code allows it. The City Code permits a house's water line and sewer connection to be extended to a detached accessory dwelling rather than requiring a separate connection. Water service in the City has been provided by Fairfax Water since the City sold its water system in 2014, so we confirm the water side with them. That can simplify the site work, although the trench still runs from the house to the cottage and the pipes have to be sized for both homes. Electrical service is worked out separately with the utility. The detached ADU section above covers the rest of the site planning.

It depends on your house. Over 1,400 square feet, the unit can be up to 1,000 square feet or half the house's gross floor area, whichever is smaller. At 1,400 or less, the cap is 700 square feet. A unit that sits completely inside the basement is only limited by the size of the basement. Lot coverage rules still apply to a detached unit, so on smaller lots coverage can be the tighter limit.

Yes, and the City's rules make that easier in one respect. Normally the owner has to be living on the property as a primary residence when the accessory dwelling's building permit and certificate of occupancy are issued. The code makes an exception for new construction where the principal dwelling and the accessory dwelling are built together. That matters if you are tearing down an older house or building on a vacant lot. We design both buildings as one plan, so setbacks, lot coverage and utility runs are worked out for the pair rather than squeezed in later.

No. The City prohibits short-term rental use of accessory dwellings, so nightly and weekend stays are out. Long-term rental is allowed, and the unit can hold up to four occupants, which suits a small household or a pair of roommates. The owner-residence rule applies when the building permit and certificate of occupancy are issued, so you need to be living on the property at those points, unless you are building a new house and unit together.

It starts with a conversation with Zoning staff to confirm the concept. The application then goes to the Development Services counter with a building permit application, an Affidavit of Compliance, a certified plat and construction plans. Once the Zoning Administrator approves, Building Safety, Public Works and Urban Forestry review it. That Urban Forestry review is why we locate big trees and their root zones before siting a cottage. During construction, wall-check and height surveys confirm the unit was built where it was approved, and the Zoning Administrator signs the certificate of occupancy.

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Our Falls Church ADU Process

First we confirm the jurisdiction. Then we measure the house, check the zoning district, lot coverage and setbacks, and look at big trees that could shape where a cottage goes. Sometimes the right answer is an ADU addition on the side of the house instead of a building in back, because attached units follow the main house's setbacks.
We handle design, plat coordination, permits and construction, and our crews stay on the job through final inspection. If you also want more space for your own household, that work can run under the same zoning review.

What You Get

A permitted accessory dwelling with its own kitchen, bath and entrance, a certificate of occupancy signed by the City, and a layout built for the person who will actually live there.
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ADU Builder in Nearby Communities

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

Plan Your Falls Church ADU

Call (703) 743-7777 with your address. We'll tell you which rules apply before we talk design.
Bring a plat or survey if you have one.

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