ADU Builder in McLean, VA

In McLean, the land is the expensive part. That's why so many owners here would rather add a second unit to the house they have than buy a bigger lot, and why the teardown crews on streets off Old Dominion Drive and Kirby Road keep busy. Either way, the timing matters. If you're rebuilding, the cheapest time to plan an accessory unit is before the foundation is poured. If you're staying put, a basement apartment or an attached wing can give a parent, an adult child or a tenant their own front door. DLA Design & Build designs and builds both, and we take the Fairfax County permits from start to finish.
A second home under your roof, planned the way the county will approve it.

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Why McLean Families Add an Accessory Unit

The most common reason we hear is family. Parents who spent forty years in a colonial in Chesterbrook don't want a condo in another county, and grown kids starting careers in Tysons or downtown can't buy in the neighborhood they grew up in. An accessory dwelling unit keeps them close without everyone sharing one kitchen. From McLean it's a short drive across Chain Bridge into the District, and the Silver Line stations at McLean and Tysons put a tenant or a working adult child on the train without a second car.
The other reason is the rebuild market. When an owner is already replacing a 1950s rambler with a new house, adding a lower-level suite with its own entrance costs far less than adding it later, because the plumbing, the egress and the separate HVAC zone go in while the walls are open.
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ADU Types We Build in McLean, VA

All eight types are possible somewhere in McLean, but on most lots here the county rules push the unit into or onto the house. Here is how each one plays out under Fairfax County's current standards.

01Detached ADU

Detached ADUs in McLean

A standalone backyard cottage is the hardest ADU to get approved in McLean. Fairfax County allows a detached accessory living unit only on a lot of at least two acres, only by special permit from the Board of Zoning Appeals after a public hearing, and caps it at 1,200 square feet. Most McLean subdivisions were platted well below two acres, so this option mostly belongs to the larger estate parcels.

If you are rebuilding on a smaller lot and think you may want a cottage someday, we can site the new house so the rear yard stays open. The county's draft amendment would allow detached units on smaller lots, but it has not been adopted. Owners with real acreage should also read our Great Falls ADU page.

02Attached ADU

Attached ADUs in McLean Homes

An attached unit shares at least one wall with the main house and has its own kitchen, bath and entrance. In Fairfax County it can go through the administrative permit as an interior ALU, as long as it connects to the main house through finished, heated and cooled interior space, not an open breezeway or an unheated garage. Any new exterior door goes on the side or rear, so the front still reads as one home.

We build the shared wall and floor as rated fire assemblies, add sound insulation, and give the unit its own HVAC zone. In a new McLean house, we frame the connecting door and the separate systems in from the start, so the space can work as a guest wing now and a unit later.

03Basement ADU

Basement Apartments in McLean

McLean has a lot of large walkout basements, and a lower level is usually the quickest route to a legal unit here. Fairfax County lets an existing basement be used in its entirety, subject to a date cutoff in the ordinance, instead of the usual cap of 800 square feet or 40 percent of the house. For sizing, the county counts basement area with at least six feet six inches of structural headroom. A basement poured as part of a new house does not get the whole-basement allowance under current rules.

The work is basement remodeling with more at stake: egress windows in every bedroom, a side or rear entrance, moisture control at the slab and walls, and smoke and carbon monoxide alarms interconnected with the main house.

04Garage Conversion

Garage Conversions in McLean

Turning an attached garage into living space keeps the unit inside the house, which fits the county's interior ALU path. Parking is the catch. A house with an ALU needs the spaces the house already requires plus one more, which the county's summary puts at three off-street spaces on a public street. Convert the garage and those spaces have to land on the driveway, but on lots of 36,000 square feet or less, front-yard paving is capped at 25 percent in the R-1 and R-2 districts and 30 percent in R-3 and R-4. On a narrow McLean lot, that math can end the idea. One wrinkle: since July 1, 2026, state law keeps the county from requiring the extra space in certain areas near transit, which the county is still defining, so a lot close to a Silver Line station may be treated differently. We check yours.

When it works, we build an insulated floor over the old slab, replace the door with a wall and windows that match the house, and bring the space up to living-space code.

05In-Law Suite

In-Law Suites for McLean Families

An in-law suite and an accessory living unit can look almost the same. In Fairfax County the difference is whether the space has everything a separate household needs, including a place to cook. A bedroom, bath and sitting room that share the family kitchen are simply part of the house. Add a kitchen for someone living there as a separate household and the county treats it as an ALU, with the owner-occupancy rule, the two-person limit, the recorded permit and the renewals.

Some families choose the simpler suite now and rough in plumbing for a kitchen later. Either way, we design for aging in place: a step-free route from the driveway, wide doors, a curbless shower with grab-bar blocking, and a bedroom on the entry level instead of up a flight of colonial stairs.

06Guest House

Guest Houses and Pool Houses in McLean

A pool house, studio or guest cottage behind a McLean house is an accessory structure, not a dwelling, as long as nobody lives in it independently. Leave out the kitchen and it does not meet the county's definition of an accessory living unit. Add one and it becomes a detached ALU, which brings back the two-acre minimum and the special permit.

Guest structures still have to meet the setbacks for your zoning district, and the county limits how much of the rear setback area can be covered. On lots of 36,000 square feet or less, the county's ALU guidance notes that all enclosed freestanding accessory structures together cannot exceed half the size of the house. We check those limits before you fall for a design.

07Above-Garage ADU

Apartments Over a McLean Garage

Where the garage sits decides this one. Finished space above an attached garage can be part of the house, so a unit there can qualify as an interior ALU if it connects to the rest of the home through finished interior space, and the garage floor area does not count toward the unit's size. A carriage-house apartment over a detached garage is a different case. The county treats a unit in a freestanding building as detached, so it needs two acres and a Board of Zoning Appeals special permit.

Building over an existing attached garage means checking whether the footings and walls can carry a second floor, and adding a fire-rated ceiling between the cars and the bedrooms.

08ADU Addition

ADU Additions in McLean

Building new space for the unit gives you the most control over the layout. A rear wing, a side addition or a second story over part of the house can hold an interior ALU, provided the unit stays under the size cap and connects through conditioned interior space. The addition follows the same setbacks, height limits and lot coverage rules as any McLean addition, and Land Development Services reviews it the same way.

On many older lots the side yards are already tight, so the unit goes to the rear or up. We match rooflines, siding and window proportions so the new wing does not look tacked on.

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How Fairfax County Regulates ADUs in McLean

McLean is unincorporated Fairfax County, so the county Zoning Ordinance sets the rules and Land Development Services issues the building permits. The county calls these units accessory living units, or ALUs. Current standards allow one ALU per lot, only with a single-family detached house. The unit can have up to two bedrooms and two occupants, and the owner has to live in either the main house or the ALU. The age and disability requirement from the old ordinance is gone.
An interior unit, whether it sits in the basement or in a new ADU addition, qualifies for an administrative permit when it stays under the lesser of 800 square feet or 40 percent of the house and connects through finished, climate-controlled interior space. An existing basement can be used in full, subject to a cutoff date in the ordinance that we confirm with the county for your house. A new entrance must face the side or rear, and the driveway and curb cut stay shared with the main house. A detached unit requires a Board of Zoning Appeals special permit, two acres and no more than 1,200 square feet.

The county has a draft amendment in front of it that would change several of these limits. As of September 2026, public hearings had not been scheduled, so we design to the rules in force. McLean also has plenty of lots near Pimmit Run, Dead Run and Scotts Run, where a stream buffer can decide where an addition goes.
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Frequently Asked Questions About ADUs in McLean, VA

Yes, and it's the easiest time to do it. An interior ALU can be designed into new construction and permitted through the county's administrative process once the house meets the standards. One catch: the whole-basement allowance is tied to basements that existed by a date in the ordinance, so a brand-new basement unit is normally held to the lesser of 800 square feet or 40 percent of the house. We lay out the suite, its entrance and its mechanical systems with that limit in mind, so nothing has to be torn out later.

Not automatically. Fairfax County treats a space as an ALU when it has everything a separate home needs: living, sleeping, eating, cooking and a bathroom. Plenty of McLean basements stop short of that. When a building permit shows a second kitchen or wet bar that isn't meant to be a separate unit, the county uses a certification form in which the owner states the space is for their own household. If you actually plan to have someone live down there independently, it's cleaner to get the ALU permit and do it right.

Yes, as long as you live on the property. The owner has to occupy either the main house or the ALU, and the unit can house no more than two people. The county's ALU guidance also says short-term lodging, the Airbnb-style kind, isn't allowed on a property that has an ALU. Being close to the McLean and Tysons Metro stations helps it rent, but the county rules decide who can live there, not the market.

The county's ALU page estimates about 30 calendar days for the administrative permit. Its December 2025 review found most approvals came through within two weeks, but roughly 40 percent took longer, usually because of back and forth over drawings or final building permits. The building permit through Land Development Services is a separate track. We submit complete packages to keep that back and forth short and plan the construction schedule around both reviews.

Probably not, unless your plan depends on them. The draft would raise the size cap, allow three occupants, drop the separate zoning permit and allow detached units on smaller lots, with a special permit for lots between 15,000 and 36,000 square feet. None of it had been adopted as of September 2026, and drafts change. If your McLean lot falls in that middle band and you really want a backyard cottage, waiting may make sense. For a basement or attached unit, the current rules already work.

Maybe. An ALU addition has to meet the same setbacks as any other addition, and the county draws no special envelope for it. Older McLean subdivisions have a lot of houses set close to one side yard, which usually pushes the addition to the rear or up. Before we sketch anything, we pull your zoning district, measure the setbacks and check lot coverage. Our McLean home additions page explains how we weigh a rear addition against a second story.

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How We Run a McLean ADU Project

We start with the parcel: the zoning district, the setbacks, any stream buffer and the existing basement's ceiling height and grade. Then we sit down with you and decide on the unit's size, where its door goes and how it connects to the house, since those three things decide whether it qualifies for the administrative permit.
Once the design is set, we submit the ALU permit and the building permit to the county and manage the comments. After construction, we help you record the approved permit in the county land records before anyone moves in and remind you when the first renewal is due.

What You End Up With

A legal second unit that looks like part of the house from the street and works as its own home inside. It's permitted and recorded, so the paperwork is in order when you eventually sell.
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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 Us About an ADU in McLean

Call (703) 743-7777 or use the form. Tell us if you're renovating or rebuilding.
We'll look at your lot and the county rules and tell you what size and layout you can realistically permit.

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