Accessory Dwelling Unit (ADU) Additions in Bethesda and Rockville
Flexible Living for Family and Income
An accessory dwelling unit gives Bethesda homeowners a private, self-contained space for aging parents, adult children, guests, or rental tenants. With Montgomery County's ADU-friendly rules and the DMV's strong rental market, a well-built ADU is one of the most versatile and valuable additions you can make to your property. Among our home additions, an ADU offers the most independent living space; when zoning or budget favors building within your existing structure, a second story addition or a finished basement remodel can be a strong alternative.
The right ADU type depends heavily on your lot. The mid-century homes around Bethesda and Chevy Chase frequently have detached garages or full basements that convert into code-compliant units economically, while their compact lots and Montgomery County setbacks shape what a detached cottage can be. The newer homes and townhomes in Rockville and the Pike District often suit attached in-law suites or above-garage units, and the larger estate lots of Potomac easily accommodate full custom detached ADUs with private utilities. If a backyard unit isn't the right fit, a light-filled sunroom addition can add flexible living space instead.
Planning the kitchen, bath, and finishes for your ADU? Our iDesign Interior Solutions showroom is in North Bethesda's Pike District, just a 5-minute drive from Rockville Town Center, making it an easy stop for homeowners across Bethesda, Rockville, Chevy Chase, and Potomac. Plan a visit to the showroom to explore materials in person.
ADU Options We Build:
- Detached backyard cottages
- Garage conversions and above-garage units
- Basement apartment ADUs with private entry
- Attached in-law suites
- Full kitchens, baths, and accessible design
Our ADU Process
- 1
Feasibility & Zoning Review
We confirm your lot's ADU eligibility under Montgomery County rules.
- 2
Design & Layout
We design an efficient, comfortable unit tailored to its use.
- 3
Permitting & Utilities
We handle ADU permits, utility connections, and approvals.
- 4
Construction
We build the unit to code with quality, durable materials.
- 5
Finishing & Handover
We complete finishes and final inspections so it is ready to live in.
Ready to Add an ADU?
Contact our team to explore an accessory dwelling unit for your Bethesda property.
Request a Consultation25+ Years Building Multigenerational Spaces in the DMV
iDesign Interior Solutions has spent more than two decades helping Bethesda and DMV families create flexible living arrangements — long before ADUs became popular. We have tracked Montgomery County's evolving accessory dwelling unit regulations closely and built independent suites and cottages that satisfy both inspectors and the families who live in them. That combination of long local tenure and current regulatory knowledge is why homeowners trust us with these uniquely sensitive projects.
25+
Years Serving the DMV
2,700+
Completed Projects
ADU
Zoning & Permit Specialists
Frequently Asked Questions About ADU Additions
Are accessory dwelling units allowed in Bethesda and Montgomery County?
Yes. Montgomery County permits accessory dwelling units in most residential zones, subject to size, parking, and owner-occupancy rules. We stay current on the county ADU regulations that apply to Bethesda properties and guide you through eligibility and approvals.
What types of ADUs can you build?
We design and build detached backyard cottages, garage conversions, basement apartment ADUs, and attached additions with a private entrance. Each is a fully independent living unit with its own kitchen and bath.
Can an ADU generate rental income in the DMV?
Yes. With strong rental demand near Bethesda, NIH, downtown DC, and the Metro, a legal, permitted ADU can produce meaningful monthly income or house extended family while adding long-term value to your property.
How long does it take to build an ADU?
Detached ADUs typically take 4-7 months including design and permitting, while garage or basement conversions may be faster. We provide a project-specific timeline at consultation.
Estimated Cost of an ADU in the Bethesda Area in 2026
| Project Scope | Estimated 2026 Cost* |
|---|---|
| Garage or basement conversionConverting existing space into a code-compliant accessory dwelling. | $60,000 – $120,000 |
| Small detached ADUA new standalone unit with kitchen, bath, and living area. | $120,000 – $200,000 |
| Full custom detached ADULarger guest house with premium finishes and full utilities. | $200,000 – $350,000+ |
*These figures are rough planning estimates only. Your actual quote will depend on in-home measurements and the current cost of materials and labor at the time of your project, as well as the specific finishes and scope you choose. For an accurate price, schedule a free in-home consultation with our team.
ADU Construction Services in the DMV Area
We design and build accessory dwelling units throughout Maryland, DC, and Northern Virginia, including:
Bethesda, MD
North Bethesda, MD
Rockville, MD
Potomac, MD
Chevy Chase, MD
Silver Spring, MD
Washington, DC
McLean, VA
Explore More Addition Services
What Our Clients Say
Five-star reviews from homeowners across the DMV area.
Kitchen Remodel & Custom Addition
This was our fourth project with iDesign in the past couple of years, and they impress us every time — the office responds quickly and the crews show up when promised. For our full kitchen renovation and custom addition, the showroom team explained every phase and worked in everything on our list. They even matched the paint and style of the addition to the rest of the house, something other contractors had told us was impossible.
Roger
Multi-Room Home Remodel
iDesign made our dream home happen. Coordinating separate contractors for a multi-room remodel had been a struggle, but working with one design team and their own crews took all of that stress away. Communication was excellent from start to finish across nearly 2,400 square feet of renovation — including the kitchen, which had felt overwhelming before. We are grateful to the whole team.
Man J.
Full Condo Remodel
Our condo received a stunning top-to-bottom remodel: a flawless kitchen transformation, a bathtub-to-shower conversion, popcorn ceiling encapsulation, and new recessed lighting that brightens the whole space. The craftsmanship is exceptional, and the customer service made a major renovation completely stress-free.
Elena D.
Second-Story Addition & Rental Prep
We were on a hectic timeline preparing our house as a rental before moving out of the DMV, and we could not have navigated it without iDesign. They built a custom second-story addition, replaced the kitchen backsplash, installed a new bathroom vanity, and repainted several rooms — and they connected us with a licensed architect for the DC permits, which saved us a huge headache. Their attentiveness and input were invaluable.
Rami B.
Emergency Repair & Bathroom Remodel
When water started leaking through our ceiling one morning, the iDesign team and their plumber were at our house within hours and quickly traced it to a pipe under the bathroom floor. The price they offered was so good that we ended up redoing the entire bathroom. The work was wonderful, finished quickly, and barely disrupted our routine — we would call them again without hesitation.
Claudia F.
Visit Our Showroom
Visit our showroom to discuss your ADU or accessory dwelling unit project with our design team.
iDesign Interior Solutions · North Bethesda, MD
(301) 881-1115 · Mon–Fri 9am–6pm · Sat 9am–6pm · Sun 10am–3pm