Turnkey ADU Builder · DC, Maryland & Northern Virginia
Your backyard could earn $2,000+/mo
A legal, income-producing backyard home, or an in-law suite steps from your door. We handle architectural design, all the permitting, and the complete build. One contract. One team.
100% turnkey
We design it, permit it, and build it.
An accessory dwelling unit is one of the highest-return improvements you can make to a home across the DC metro, added rental income and six figures of equity from a single build. We handle architectural design, every local permit, and the complete construction. You just turn the key.
The NoVA ADU reality
Three things that derail most ADU projects.
We built our process to remove each one.
The zoning maze
Setbacks, lot coverage, owner-occupancy rules, NoVA's ADU regulations differ by county and change often.
Hidden costs
Surprise utility connections, impact fees, and change orders can blow up a budget mid-build.
Juggling vendors
Architect, engineer, expediter, GC, inspectors, coordinating them all is a part-time job.
Process
How long does it take to build an ADU?
Typical total: 5–8 months. One team, start to finish.
Custom ADU Design
We design an ADU tailored to your lot, goals, and budget, and prepare the drawings for permitting.
All NoVA Permits
We file and manage every permit and approval through your county or city, you don't chase a single office.
Build & Key Delivery
We build it turnkey and hand you the keys, ready to rent or move family in.
Design, permit, and build under one contract. We design an ADU around your lot and your goals, whether that is rental income or housing aging parents. We handle the zoning research and permitting, including Fairfax County zoning, and then we build it, so design, permitting, and construction stay with one team.
Planning ahead? See our ADU cost guide for Northern Virginia and our Fairfax County ADU zoning guide.
Cost & return
How much does an ADU cost, and what can it earn?
Illustrative 600 sq ft detached ADU in the Annandale / Fairfax area.
600 sq ft detached ADU · Annandale / Fairfax
A snapshot of typical economics, your numbers depend on lot, design, and finishes.
Estimate your ADU
Ballpark your build cost and rental income.
Slide your ADU size and pick your area for a quick estimate. When you’re ready, answer 4 quick questions and our team will review your property and follow up.
Illustrative estimate only, not a quote or financing offer. Actual cost depends on design, site conditions, and finishes. Rent: Apartment List, Annandale rent report, October 2026, overall median for all apartment sizes, not an estimate for your unit.
Get your property reviewed →Transparent pricing
No surprises, just the home you signed up for.
- Transparent, upfront pricing, no surprise change orders.
- Design, permits, materials, and build in a single contract.
- A dedicated project manager from first drawing to final inspection.
- Industry-leading warranty on labor and materials.
Prefer to pay over time? Financing is available →
Across the DC metro
We design and build ADUs in DC, Maryland, and Northern Virginia.
Regulations last verified: September 2026
We are headquartered in Gaithersburg, Maryland, and we build across the DC metro. Over 20+ years we have completed 2,500+ projects across Washington DC, Maryland, and Northern Virginia, including extensive remodeling work throughout Montgomery County. We design and build accessory dwelling units across all three, and we handle the zoning research and permitting for you.
One advantage worth knowing: in Maryland we handle design in-house, so drawings, permits, and construction stay under one roof and one contract. In Virginia and DC we work with a licensed architect partner for the design drawings, then manage permitting and construction the same way.
Montgomery County, Maryland
In unincorporated Montgomery County (Bethesda, Chevy Chase and more; the cities of Rockville and Gaithersburg set their own ADU rules), an ADU runs through two departments: a Class 3 Accessory Dwelling Unit license through DHCA, plus building permits through the Department of Permitting Services (DPS). Since October 5, 2026, an attached or detached ADU must be “not greater than 75% of the size of” the primary single-family detached dwelling unit. Under DHCA’s license rules, the ADU must be in the owner's primary residence, and every owner must show proof of residency; the zoning code allows one ADU per lot, with no more than two occupants aged 18 or older, and an ADU cannot be on a lot where a short-term residential rental exists or is licensed.
Fairfax County, Virginia
In Fairfax County, ADUs are officially Accessory Living Units (ALUs), permitted on single-family lots, one per property, capped at two bedrooms and two occupants, with owner-occupancy of either the home or the ALU. An interior or attached ALU is limited to 800 square feet or 40% of the principal dwelling's gross floor area, whichever is less, and can be approved by administrative permit; a detached ALU is 1,200 sq ft, permitted only on lots of at least two acres, and requires a special permit with a Board of Zoning Appeals public hearing. Properties on well or septic need Health Department approval first. The administrative permit fee is $285 application, $75 renewal, and the county estimates approximately 30 calendar days to process. Full details are in our Fairfax County ADU zoning guide.
Northern Virginia (Fairfax, Arlington, Alexandria) and Washington DC each have their own rules. For a full jurisdiction-by-jurisdiction breakdown, see our guide to ADU rules in DC, Maryland, and Virginia.
Free property review
Find out if your property qualifies.
Answer 4 quick questions. Our ADU team reviews your property and follows up with your options.
What's your main goal for an ADU?
Reviews
Rated 5.0 by local homeowners.
Hands down the best contractor experience I've had. They completely transformed my bathroom, the craftsmanship, attention to detail, and professionalism were exceptional throughout.
After a flood hit my home, Excell took all the pressure off, drywall, flooring, painting, plumbing, electrical. My home looks better than it did before the flood.
Excell did an amazing job remodeling my kitchen. Professional, communicative, and paid attention to every detail, the quality exceeded my expectations.
Excell Homes is very professional. I couldn't be happier with my new farmhouse sink, their work completely transformed my kitchen. Highly recommend.
Extremely satisfied with my experience. My project manager, Luis Bonilla, was superb, I credit him with the success of my two bathrooms.
A great company that does its due diligence on every job, commercial or residential. They go above and beyond, excellent service start to finish.
Excellent service from Excell Homes! They gave my bathroom the modern look it needed. I highly recommend them and will use them again.
ADU FAQ
Questions homeowners ask us.
Can I build an ADU in Fairfax County, Arlington, or Alexandria?
In most cases, yes, each jurisdiction has its own rules on lot size, setbacks, and owner-occupancy. We assess your property up front and handle the zoning and permitting for you.
How much does an ADU cost to build in Northern Virginia?
A turnkey 600 sq ft detached ADU typically runs about $150K–$200K, depending on size, finishes, and site conditions. We give you a clear, upfront price before you commit.
How long does an ADU take from start to move-in?
About 5–8 months in total: 2–4 weeks of design, 1–3 months of permitting and review, 12–16 weeks of construction, then 1–2 weeks of final inspections.
How much rent can an ADU earn?
In Annandale the overall median rent, across all apartment sizes, is $2,184/mo, down 5.0% year over year (Apartment List, Annandale rent report, October 2026). The report does not break rent down by bedroom count, and what an ADU earns depends on its size, finish and location.
Are there rules on short-term rentals or owner-occupancy?
Short-term lodging, stays under 30 days like Airbnb, is not permitted in an ADU in Fairfax County, so an ADU is a long-term rental (leases of 30 days or more). Owner-occupancy rules also vary by jurisdiction. We walk you through what applies to your property during design.
Can I finance an ADU?
Yes. Through our RenoFi partnership you can finance your ADU based on your home's after-renovation value. See our financing page for details.
This guide is for general informational purposes only and does not constitute legal, zoning, or professional advice. Accessory dwelling unit rules vary by property, zone, and lot size, and they are actively changing. Several jurisdictions in the DC metro are currently reviewing or revising their ADU regulations, including Fairfax County. The information here reflects our understanding at the time of writing and may become outdated. Nothing here is a guarantee that a given project is permittable. Always confirm current requirements for your specific property directly with the relevant authority (the DC Office of Zoning and Department of Buildings, the Montgomery County Department of Housing and Community Affairs and Department of Permitting Services, or Fairfax County Planning and Development) before making decisions or beginning a project. Excell Homes is not responsible for actions taken based on this information.
Ready to unlock your backyard?
Tell us about your property and goals. We'll come back with a detailed ADU plan and upfront pricing.