A Tranquil, Court-side Guest Cottage: ADU Remodeling in Metro DC

Accessory Dwelling Units—known as ADUs—are gaining attention among homeowners in the Washington DC metro area for their ability to flex with evolving family needs. 

Whether it’s creating a peaceful place for an aging parent, giving adult children space to launch into independence, or designing a retreat for guests, ADUs offer a way to add highly functional, private living space within your existing property.

But what does an ADU really look like in practice? And how do zoning, design, and long-term planning shape the final result? Let’s take a closer look at one recently completed Gilday Renovations project—and what it reveals about building guest cottages and ADUs in our region.

A Tennis House Becomes a Thoughtful Guest Cottage in Olney

When our clients in Olney, Maryland first approached us, they had a unique structure on their property: a small tennis house tucked near the court. Their initial vision was to transform it into a private, one-bedroom cottage for a father-in-law who might eventually move in.

Though that need changed with time, the family recognized the value of having an independent living space steps from the main home. They reimagined the space as a multi-purpose guest cottage—one that could support adult children visiting with families and serve as a comfortable retreat for relatives.

What began as a modest outbuilding is now a fully self-contained living space featuring:

• A sitting area and bedroom
• Compact kitchenette
• Full bath and laundry closet
• Thoughtful layout that maximizes privacy and comfort

The entire design is tailored specifically to the family’s lifestyle.

What Makes It an ADU? (And What Doesn't)

Not every backyard structure qualifies as an ADU. Here in the DC area, an accessory dwelling unit must meet specific criteria, including:

• A separate entrance
• A kitchen with a stove
• A bathroom

This distinction matters. For example, a guest suite with a wet bar, microwave, and full bathroom may function like an apartment—but unless there’s a stove, it typically won’t trigger the same zoning or permitting requirements. Once you cross into “full kitchen” territory, strict local regulations kick in.

And those rules vary widely by jurisdiction.

Navigating Zoning Across the DC Metro Area

Montgomery County, DC, and Northern Virginia all have unique rules around ADUs—and even within each county, zoning requirements differ from neighborhood to neighborhood.

A few examples:

• Detached accessory buildings often benefit from smaller setbacks from the rear and side property lines
• However, many zones enforce lot coverage limits—meaning you can’t exceed a prescribed percentage of your lot with built structures
• DC’s higher-density neighborhoods may allow smaller setbacks but come with their own layers of permitting

Bottom line: Always check zoning and permitting requirements early in the planning phase. A qualified design firm will help guide that process so you can explore what’s feasible for your lot and goals.

Detached vs. Attached: What’s the Right Fit?

In the Olney project, the decision to remodel an existing detached structure was easy—the tennis house was already there, and the clients had the acreage and septic capacity to support it.

But not every homeowner has that luxury. Sometimes, an attached ADU (perhaps over a garage or off the back of the home) is a better fit, particularly if:

• You’re working within tighter setbacks
• You want to simplify utility tie-ins (water, electric, septic)
• You’re caring for an aging parent who benefits from closer proximity

A detached ADU, on the other hand, may be preferable when:

• You want more privacy or separation for guests or adult children
• You're working with an existing garage or outbuilding
• You’re planning for long-term uses that require true independence

Each option brings trade-offs. Design should always follow your family’s lifestyle, future plans, and the realities of your property.

Why Aren’t ADUs More Popular? A Reality Check on Cost and Code

Despite growing interest, ADUs remain relatively rare in the DC metro region—and cost is a major reason.

Building a detached guest cottage with a full kitchen, bathroom, and separate utilities is often more expensive than people expect, especially when:

• You need new septic systems or separate power lines (as in the Olney project)
• You have to extend water lines or install a generator
• You’re designing to meet accessibility requirements for aging-in-place

Adding to the challenge are strict regulations around how ADUs can be used:

• Many jurisdictions require an owner to live on-site
• Renting out the unit may be prohibited or require special covenants
• Certain design elements—like including a stove—can shift the classification entirely

With high interest rates and zoning restrictions, some homeowners put their ADU plans on hold. But for those who prioritize family, flexibility, and long-term value, the investment can be well worth it.

Designing with Purpose: Tips for a Smart, Adaptable ADU

If you’re considering an ADU project, here are a few strategies to keep in mind:

• Stack your utilities. In the Olney project, placing the kitchen, bathroom, and laundry along a shared wall saved space and streamlined plumbing.
• Plan for aging in place. Ground-level units, wide doorways, and accessible bathrooms make long-term living easier.
• Face for privacy. Orienting windows and entrances away from the main home creates separation—even when just a few feet apart.
• Design for now and later. Whether it starts as a guest suite or office, thoughtful design allows an ADU to flex as your family’s needs evolve.

Is an ADU Right for You? Key Questions to Ask

Before you begin designing, ask yourself:

• Do I have enough available space to build an ADU?
• Who will use it, and how might that change over time?
• Am I prepared for the zoning and permitting process?
• Do I want something detached for privacy, or attached for convenience?

Answering these questions upfront can help clarify your vision—and determine the right path forward.

Closing Thoughts: A Space That Grows with You

The Olney guest cottage started as a place for an aging parent. It became a flexible, beautiful retreat for guests or adult children—and a long-term investment in family connection.

At Gilday Renovations, we approach every ADU project as an opportunity to create custom, purposeful space that blends seamlessly into your property and your life. With the right design, you can build something that serves your family for years to come.

Want to learn more about how to explore the idea of building an ADU on your property, then please consider downloading the free eBook, "What Every Homeowner Needs to Know About Home Additions and Whole House Remodeling" or contact us for a discussion about your renovation project.