Build Your ADU in Fairfax County, VA
Makara ADU designs, permits and builds accessory dwelling units to Fairfax County’s rules, and builds nothing else.
- ADU max size
- Detached: 1,200 sq ft · Attached: lesser of 800 sq ft or 40% of the main house
- Minimum lot size
- No minimum
- Detached unit lot minimum
- 87,120 sq ft
- Owner occupancy
- Required
- Off-street parking
- Three spaces total on a public street · four on a private street
- Allowed by
- Right, in permitted zones
- Licensed & Insured in Virginia (Class A 2705184565)
- Fairfax County ADU Specialists
- Full-Service: Design → Permits → Build
- Free Property Eligibility Assessment
Can you build an ADU in Fairfax County, VA?
Fairfax County ADU Guidelines
The rules that decide whether, and what, you can build. The table below carries the specifics.
Detached: 1,200 sq ft
1,200 sq ft · lot of at least 2 acres · Board of Zoning Appeals special permit · 800 sq ft or 40% of the principal dwelling, whichever is less · administrative permit
Permitted by right
All residential zones. No minimum lot size.
Where the unit can sit
Front: 35 ft · Side: 10 ft · Rear: 10 ft
Off-street spaces
Three spaces total on a public street · four on a private street
Owner must live on site
Maximum two bedrooms and two occupants in the unit
Governing ordinance
Fairfax County Zoning Ordinance §4102.7 (zMOD) — Accessory Living Units
Check Your Address
Run our free eligibility check and get Fairfax County’s rules applied to your exact lot in about a minute.
Check my property →| Requirement | Fairfax County standard |
|---|---|
| Allowed by | Right, in permitted zones |
| Minimum lot size | No minimum |
| Minimum lot size (detached) | 87,120 sq ft (about 2 acres) |
| Permitted zones | All residential zones |
| Maximum size | Detached: 1,200 sq ft · Attached: lesser of 800 sq ft or 40% of the main house |
| Detached maximum | 1,200 sq ft · lot of at least 2 acres · Board of Zoning Appeals special permit |
| Attached maximum | 800 sq ft or 40% of the principal dwelling, whichever is less · administrative permit |
| Setbacks | Front: 35 ft · Side: 10 ft · Rear: 10 ft |
| Parking | Three spaces total on a public street · four on a private street |
| Owner occupancy | Required |
| Garage or basement conversion | Allowed |
| Who may live there | Maximum two bedrooms and two occupants in the unit |
| Ordinance | Fairfax County Zoning Ordinance §4102.7 (zMOD) — Accessory Living Units |
| Rules current as of | 2023-01-01 |
If your plan is a unit for a parent, an adult child or other family member, and your lot is under two acres, the practical route in Fairfax today is to add the ADU inside the house, or as an addition to the house. A basement conversion, a bedroom wing, or an addition can all qualify, and those are approved administratively. Makara ADU will work with you to design and build the perfect fit for your family and your property.
The Fairfax County ADU Permit Process
Makara ADU handles this entire process from design to move-in, full turn-key.
- 01
Zoning & Eligibility
Confirm the lot area and whether you are pursuing an interior, attached or detached unit; a detached unit needs two acres. Makara ADU does this free with our property eligibility checker.
- 02
Design & Drawings
Architectural and structural plans to the county's residential code, sized to 800 square feet or 40% of the house for an interior or attached unit, or up to 1,200 square feet for a detached one.
- 03
ADU Permit (County)
File the administrative permit for an interior or attached unit, or the special permit and Board of Zoning Appeals hearing for a detached one. Makara ADU handles this for its clients.
- 04
Building Permits & Build
Building and trades permits from the county; construction proceeds with county inspections along the way.
- 05
Final Inspection & Occupancy
The county's final inspection and occupancy approval, then keys in hand, ready to occupy or rent.
Fairfax County’s ADU Specialists
We don't build everything. We build ADUs. Based in Gaithersburg, we work with local permitting offices every week and know how each jurisdiction's rules shape what can be built.
Local Rules, Known Cold
Every jurisdiction we serve has its own size limits, setbacks, parking and occupancy rules. We track them, and the eligibility checker on this page runs on that same data.
One Contractor, Start to Finish
Architecture, engineering, permits, foundation, framing, MEP, sprinklers, finishes, and the rental license — Makara ADU manages everything under one contract. No coordinating separate architects, engineers, and builders.
Fixed-Price Proposals
We quote your project in full before a shovel goes in the ground. No surprise change orders mid-construction — we plan for lot coverage, stormwater, and utility connections up front.
Built for Aging in Place & Family
Most of our Fairfax County clients build to keep aging parents or adult children close. We design single-floor, accessible units that work beautifully today and adapt gracefully over time.
ADU Types We Build in Fairfax County
Most jurisdictions allow more than one ADU configuration. We help you choose the right one for your lot, your zone and your goals.
Detached Backyard Cottage
A fully independent structure in your backyard with its own entrance, kitchen and bath. The most flexible option, and the one most people picture. Size and placement follow the rules in the table above.
Attached Second Home
Add an attached ADU with its own separate entrance, kitchen, and bath. Makara ADU will collaborate with you to design the space to be functional to meet your needs while creating an aesthetically pleasing space that will add value to your life, family and your home.
Basement and Garage Conversions
Convert an existing garage or basement into a legal, licensed ADU — the most cost-effective path to added living space, and often faster to permit than new construction.
ADUs We’ve Built Recently
A sample of ADUs we’ve built across Northern Virginia.
Fairfax County ADU FAQ
Is there a minimum lot size for an ADU in Fairfax County?
Not for a unit inside or attached to your house. There is for a detached one: the lot must be at least two acres, which is 87,120 square feet.
How big can an accessory living unit be in Fairfax County?
A detached unit may be up to 1,200 square feet. An interior or attached unit is capped at 800 square feet or 40% of the gross floor area of the house, whichever is less.
Can I rent out an accessory living unit in Fairfax County?
You can let the unit, but either the unit or the main house must be owner-occupied, so you cannot move out and let both. Occupancy of the unit is limited to two people.
Do I need extra parking?
Yes. A property with an accessory living unit needs three parking spaces in total if it is on a public street, or four if it is on a private street.
How long does approval take?
An administrative permit for an interior unit is the faster route and does not require a hearing. A detached unit needs a special permit from the Board of Zoning Appeals, which adds a public hearing and takes considerably longer.
Are the rules likely to change?
Possibly, in the near future. Fairfax County is considering a Zoning Ordinance amendment for accessory living units that would simplify the process and could ease the current rules, including the two-acre minimum for a detached unit. Public hearings are scheduled before the Planning Commission on October 29, 2026 and the Board of Supervisors on November 17, 2026. Until the Board acts, the rules on this page are the ones in force, and we will update it if they change.
Is Your Fairfax County Property Eligible for an ADU?
Use our free eligibility checker to find out in about a minute, and get a personalized report sent to your inbox.