Maximize Value and Space with Winthorpe's ADU Solutions

At Winthorpe Design & Build, we believe that every inch of your property holds a world of potential. With our commitment to innovative design and superior craftsmanship, we can help you unlock that potential with our custom-built Accessory Dwelling Units (ADUs). Whether you’re looking to accommodate extended family or simply wish to expand your living space, our ADUs are the perfect solution. We take pride in our reputation for delivering high-quality, personalized spaces that reflect your needs and lifestyle.

What is an Accessory Dwelling Unit (ADU)?

An Accessory Dwelling Unit (ADU) refers to a secondary housing unit located on the same property as a primary single-family home.

There are three main types of ADUs:

  • Detached ADU: A detached ADU is a separate, free-standing structure that is located on the same lot as the primary residence. It can be built from scratch or converted from an existing structure, such as a shed or garage. Detached ADUs are often referred to as “backyard cottages” or “granny flats.”
  • Over Garage ADU: This is a type of detached ADU that is built above an existing garage. This type of ADU can be a great way to add extra living space without taking up any additional land. Over garage ADUs can be accessed from inside the garage or from the outside.
  • Attached ADU: This type of ADU is physically attached to the primary residence. It can be built as an addition to the side or rear of the house, or it can be converted from an existing space, such as a basement or attic. Attached ADUs are often used as in-law suites.

ADUs can be built from the ground up, converted from existing structures, or added as extensions to an existing home. They can be used for a variety of purposes, including housing family members or providing a place for guests to stay.

ADUs are becoming increasingly popular for the benefits they offer. In some jurisdictions, ADUs are exempt from certain zoning restrictions, which makes them an attractive option for homeowners.

Here are some of the benefits of ADUs:

  • They can provide additional housing for family members or guests.
  • They can increase the value of your home.
  • They can be used to house people with disabilities or other special needs.
  • ADUs allow for multi-generational living, where elderly parents or adult children can reside close to the main household.

Assisted Living Facility vs ADU

Assisted living facilities can be very costly, charging between $15,000 to $20,000 per month. However, constructing an ADU on your property can be a money-saving option. By having your parents live with you in the ADU, you avoid paying those expensive assisted living fees. Moreover, adding an ADU can boost the overall value of your property. Thus, with an ADU, you not only save money but also increase your home’s worth and enjoy the convenience of having your parents nearby.

ADU Rental Income in the DC Area

Maryland counties do not allow homeowners to make money from renting out their ADUs. However, the rules are different in the DC area. If you’re a homeowner in the DC area, you can list your property on AirBnb and have the opportunity to derive income from from your property.

However, you should be aware of the Airbnb 90-day rental policy. This means you can only rent out your ADU for a maximum of 90 days per year on Airbnb.

Benefits of Renting Out Your ADU in DC

Renting out your Accessory Dwelling Unit (ADU) in the Washington, D.C. area can bring several advantages. Let’s explore these benefits:

  1. Extra Income: By listing your ADU on Airbnb or other short-term rental platforms, you can generate additional income. It’s a great way to make the most of your property and increase your financial flexibility.
  2. Pay Off Your Investment: If you financed the construction of your ADU, renting it out can help you pay off the investment faster. The rental income can contribute to covering the construction costs.
  3. Flexibility: With short-term rentals, you have the flexibility to choose when to make your ADU available for guests. You can rent it out during peak seasons or special events while keeping it for personal use when needed.
  4. Tourism Demand: Being in the vibrant city of Washington, D.C., your ADU can attract tourists and business travelers throughout the year. The demand for short-term rentals in the area provides an opportunity for steady bookings.
  5. Meeting New People: Hosting travelers in your ADU allows you to connect with people from different backgrounds and cultures. It can be a rewarding experience to share your space with guests and create positive memories for them.
  6. Tax Benefits: Depending on your specific situation and local tax regulations, you may be eligible for certain tax benefits related to short-term rentals. It’s essential to consult with a tax professional to understand the potential advantages.
  7. Property Value: Renting out your ADU can add value to your property, as it demonstrates the versatility and income-generating potential of your home. This could be beneficial if you ever decide to sell your property in the future.
  8. Supporting Local Economy: By participating in short-term rentals, you contribute to the local economy by supporting tourism and other businesses in the area.

Remember, before renting out your ADU, it’s important to familiarize yourself with local regulations and zoning laws in Washington, D.C. Ensuring compliance with these rules will help you have a smooth and successful experience as a host.

How Much Does It Cost to Build an ADU in Maryland?

The actual cost of an ADU will vary depending on a number of factors. Here are some of the factors that can affect the cost of an ADU:

  • ADU Size: The larger the ADU, the higher the cost.
  • ADU Location: Building ADUs in rural areas is cheaper than in urban areas.
  • Materials Used: The cost of building an ADU with high-quality materials will be higher than the cost of building an ADU with less expensive materials.
  • Local Labor Costs: Labor expenses differ across jurisdictions, with some areas having higher costs.
  • Build Complexity: Complex builds, like those on slopes or with custom features, cost more than simpler ones on flat lots with standard features.
  • Permit and Inspection Costs: The expense of permits and inspections varies by jurisdiction, sometimes proving to be substantial.

Examples of Actual Costs of Building ADUs in Maryland

Note: These are just examples. As stated above, the cost of building an ADU may be affected by several factors.

Type of ADU Cost Square Footage Cost per Square Foot
Detached ADU $150,000 1,200 sq ft $125/sq ft
Over Garage ADU $100,000 800 sq ft $125/ sq ft
Attached ADU $75,000 800 sq ft $94/ sq ft

In addition to these costs, homeowners usually need to budget approximately $100,000 for driveway installation and site development, which are essential components of the project.

A Real-Life Example of an ADU Project

In Rockville, Maryland, Winthorpe Design & Build constructed an ADU above a garage. The client sought a separate living space for his mother while maintaining a connection to the main house. Challenges included achieving autonomy with accessibility. The ADU features a main sitting area, kitchen with laundry, and bedroom. The team added an elevator setup for future use. Renovations were done in the basement, bookshelves were customized, and window placements and roof lines were modified. Radon mitigation and heating and cooling systems were incorporated. Unexpected issues were tackled creatively. The project met the client’s expectations, resulting in a transformed and cohesive living space. To read more about this space, click here.

Projects like the one described above typically cost $200,000 to $300,000. Here are some factors which influenced the total cost of the project:

  1. Design Complexity: The client’s specific requirements, such as creating a separate living area with a bedroom, bathroom, kitchen, and laundry facilities while maintaining a connection to the main house added to the design complexity, which affected the overall cost.
  2. Additional Features: Incorporating features like an elevator setup for future use, larger windows, clerestory windows for more natural light, and a pocket door to save floor space contributed to additional costs.
  3. Radon Mitigation: As part of our commitment to building a safe environment, we incorporated radon mitigation into the project design. Choosing an active system, which is more effective than a passive system, was another cost factor.
  4. Renovations and Modifications: Apart from building the ADU, we also renovated the client’s basement, building custom bookshelves, installing a new laundry room, and modifying window placements and roof lines.
  5. Heating and Cooling System: Installing a mini-split system for the ADU to allow independent temperature control was an extra expense.
  6. Unexpected Issues: The unrepaired leak that caused water damage in the bathroom led to a complete renovation of that area. Addressing unforeseen issues like this add unexpected costs to the project.
  7. Client Preferences: Incorporating specific features requested by the client, such as preferred floor tiles, larger windows in the office, and a preferred kitchen cabinet color, contributed to the overall cost.
  8. Aesthetic Compatibility: Ensuring the ADU’s appearance matches the existing house and neighborhood required additional design considerations and materials that aligned with the overall aesthetic, influencing the cost.

General Rules and Requirements for ADUs in Maryland

Before you begin constructing your ADU in Maryland, it’s essential to understand the rules and requirements. They serve as critical guides to ensure safety, maintain community aesthetics, and guarantee that ADUs benefit all involved. The rules determine the size of your ADU, its location, and more. Failing to know or follow these could result in setbacks, like having to redo parts of the construction, or even face penalties.

Here are the general rules:

  • Each type of ADU must not exceed the maximum size allowed.  Below are the maximum sizes for each type:
    • Detached ADU – 1,200 sq ft
    • Over Garage ADU – 800 sq ft
    • Attached ADU – 800 sq ft
  • Every ADU must have its own entrance.
  • A detached ADU must be located on the same lot as the primary residence.
  • An over garage ADU must be located above an existing garage.
  • An attached ADU must be attached to the primary residence.
  • All ADUs must meet all applicable zoning and building codes.

It’s important to note that there may be additional rules or requirements that vary depending on the jurisdiction. For instance, some jurisdictions may require that ADUs have a minimum size, or that they be located a certain distance from the primary residence. Another noteworthy example is that Howard County only lets you attach an ADU to the house while other counties let you build in the backyard.

Codes are likely to become more and more universal so that each local county doesn’t have to enforce different restrictions on how you can build your ADU. But until then, each county will abide by different codes.

If you are considering building an ADU in Maryland, it’s best to consult with professionals at Winthorpe Design & Build to make sure that the structure is code-compliant.

Why Choose Winthorpe Design & Build?

Choosing a partner for your ADU project is a significant decision. Here’s why you should entrust this task to Winthorpe Design & Build:

  1. Customized Designs: We believe in creating spaces that resonate with your unique style and functional requirements. Our designers work closely with you, turning your vision into a meticulously planned design. Whether you prefer a traditional aesthetic, a sleek modern look, or anything in between, we are equipped to bring your dream ADU to life.
  2. Comprehensive Services: Our team offers a complete suite of design and build services. From initial consultation, planning, and design to construction, finishing, and clean-up, we handle every aspect of the project. This holistic approach not only ensures consistency and quality at each stage but also simplifies the process for you.
  3. Expert Team: Our team is our strength. Winthorpe professionals bring years of industry experience and a wealth of knowledge. We’re dedicated to precision, attention to detail, and adherence to the highest industry standards, ensuring a finished product you’ll be proud of.
  4. Regulatory Knowledge: Navigating local zoning laws and construction regulations can be complex. Our team has a deep understanding of these requirements. This regulatory knowledge, combined with our strong relationships with local authorities, allows us to navigate the approval process smoothly, ensuring your project stays on time and within budget.
  5. Quality Materials: The durability and finish of your ADU depend largely on the materials used. We source only the highest quality materials and equipment, ensuring longevity and durability in our builds. We strike a perfect balance between aesthetics and practicality, creating spaces that are not only beautiful but also built to last.
  6. Transparent Communication: We believe in open, honest communication. At every stage of your project, we keep you informed about the progress, any challenges encountered, and the steps we’re taking to address them. Our team is always accessible to answer your questions and address any concerns you may have.
  7. Exceptional Customer Service: We measure our success by your satisfaction. From our first meeting to the final walk-through and beyond, we strive to exceed your expectations. Our goal is to not just complete a project, but to build a lasting relationship with you.
  8. Privacy: At Winthorpe, we understand the importance of giving you space during our work on your ADU. You can count on us to stay out of your way and respect your home while delivering top-notch results.

With Winthorpe Design & Build, you’re not just getting a service – you’re becoming a part of a family that values trust, quality, and customer satisfaction above all else.

Your Dream ADU Is Just a Call Away

By choosing Winthorpe Design & Build, you’re not just investing in an Accessory Dwelling Unit; you’re investing in a stress-free construction experience, exceptional craftsmanship, and a home addition that will bring value and joy for years to come.

Reach out to us today to discuss your project. Let us show you how we can transform your property with our unique, tailor-made Accessory Dwelling Units. We look forward to creating with you!


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ADUs offer a combination of financial and social benefits. It allows you to live together with your family in the home you’ve always loved while letting everyone maintain some independence.

If you currently live in Maryland, Washington DC, or the surrounding areas, we invite you to schedule a free in-home consultation. We look forward to meeting with you!