Understanding Accessory Dwelling Units in Washington DC

If you're a DC homeowner who’s ever typed "Can I build an ADU in DC?" into Google, you’ve probably run into a mess of government sites, legal jargon, and confusing acronyms. As someone who’s built an ADU herself (before it was trendy!), I can tell you firsthand: it shouldn’t be this complicated.

But the good news? It’s not impossible. In fact, DC’s zoning rules were updated in 2016 to explicitly allow accessory apartments (aka ADUs) in almost every residential zone — as long as you meet certain conditions.

After a great roundtable discussion with leaders from the DC Office of Planning, Office of Zoning, and Department of Buildings (DOB), here’s a clear breakdown of what’s allowed and how to get started. Let's dive in!

As the housing landscape in Washington DC continues to evolve, Accessory Dwelling Units (ADUs) have emerged as a popular and innovative solution to address the city's growing housing needs. Understanding the regulations, benefits, and challenges of building ADUs in the nation's capital is essential for homeowners, developers, and policymakers alike. In this blog post, we will explore the ins and outs of ADUs in Washington DC, including the regulations governing their construction, the potential benefits they offer, and the steps involved in building these secondary units on residential properties. Join us as we delve into the world of ADUs and uncover how these unique living spaces are shaping the future of housing in DC.

Introduction to Accessory Dwelling Units (ADUs)

First, let’s clarify some terms.

• Accessory Dwelling Unit (ADU): Common, universal term used to describe a backyard cottage, basement apartment, garage apartment, or tiny home.
• Accessory Apartment: The technical term used in DC’s zoning code — same idea, different label. This is the term you'll want to use when speaking with any from the local planning or zoning department in DC
• Affordable Dwelling Unit (ADU): A completely different thing. This is part of DC’s affordable housing program — not what we’re talking about here.

Accessory Dwelling Units, commonly referred to as ADUs, are self-contained living spaces that are secondary to the primary residence on a property. These units can take various forms, such as a separate apartment, a basement suite, or a converted garage. ADUs are designed to provide additional housing options within existing residential properties, offering flexibility for homeowners and potential rental opportunities.

ADUs have gained popularity in recent years as a response to the increasing demand for affordable housing and the need for more sustainable urban development. They provide a means for homeowners to maximize the use of their property while simultaneously addressing the housing shortage in cities like Washington DC.

The concept of ADUs is not new, as they have been present in many communities for decades. However, their recognition and acceptance as a viable housing solution have grown significantly in recent years. With the changing demographics and evolving housing preferences, ADUs have become a practical and desirable option for homeowners to expand their living space or generate additional income.

In the next sections of this blog post, we will delve into the regulations for building ADUs in Washington DC, the benefits they offer, the challenges they may present, and the step-by-step process involved in constructing an ADU in the city. By the end of this comprehensive guide, you will have a thorough understanding of ADUs in Washington DC and be well-equipped to navigate the opportunities and considerations associated with these additional dwelling units.

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Regulations for ADUs in Washington, DC

Building an Accessory Dwelling Unit (ADU) — referred to as an "Accessory Apartment" in DC’s zoning code — is allowed in most residential areas of Washington, DC. However, it’s governed by specific regulations around zoning, size, location, and permits. Understanding these requirements is key to moving forward confidently and legally.

In this section, we’ll walk through the size and structure limitations, permit requirements, and zoning regulations that apply to ADUs in DC.

Size and Structure Limitations

DC allows ADUs in two main forms: attached units (like basement conversions) and detached units (like backyard cottages). Depending on your zoning district and the type of ADU, size and structure rules apply:

• Maximum Size:
  • Attached ADUs are limited to 35% of the gross floor area of the principal residence.
  • Detached ADUs must meet lot occupancy limits and other dimensional restrictions based on your zone.
• Minimum Lot Size: Your lot must include at least 1,200 square feet of gross land area to qualify for a detached ADU.
• Height Limits:
  • Detached ADUs may be up to 22 feet tall or two stories, depending on the zone and location on the lot.
• Yard and Setback Requirements: Detached ADUs must meet rear yard and side setback requirements, typically ensuring enough distance from property lines and neighbors.
• Number of Units: Only one accessory apartment is allowed per lot.

Building Permit Requirements

Before you start construction, you’ll need permits from the Department of Buildings (DOB). The process includes plan review and inspections to ensure your ADU complies with DC’s building code.

Key steps include:

• Preliminary Design Review Meeting (PDRM): This optional but highly recommended one-on-one meeting helps clarify requirements and feasibility based on your site. There are two types:
  • Zoning PDRM – to confirm zoning compliance (e.g. use, lot coverage)
  • Plan Review PDRM – to review construction documents
• Building Plan Submission: Submit detailed drawings showing floor plans, elevations, structural design, and utilities.
• Permit Fees: Fees are based on project size and complexity and are typically assessed during the application process.
• Required Inspections: Your project will go through multiple inspections during construction, including foundation, framing, electrical, plumbing, and final.

Zoning Regulations

Zoning determines whether you’re allowed to build an ADU on your property and under what conditions. Most residential zones (R-1, R-2, R-3, etc.) allow ADUs — but the details vary by zone type.

Important zoning factors:

• Zoning District: Use DC’s Zoning Map or PropertyQuest to find your zone. ADUs are allowed in most residential zones, with differing standards.
• Occupancy Requirement: In some zones (like R-1), the property owner must live on-site — either in the main dwelling or the ADU.
• Lot Occupancy Limits: Detached ADUs count toward lot occupancy. Each zone has its own max percentage — typically 40–60% — so your plans must fall within that.
• Parking Requirements: In many zones, parking requirements have been reduced or waived for ADUs, especially near transit corridors. Always confirm with DOB during your PDRM.
• Rental Restrictions: ADUs may be rented long-term in most cases. Short-term rental rules (e.g. Airbnb) are governed separately under DC’s short-term rental regulations and may have additional requirements.

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Benefits and Challenges of Building ADUs (or Accessory Apartments) in DC

Building an Accessory Dwelling Unit (ADU) in Washington DC comes with a range of benefits and challenges. Understanding these factors is essential for homeowners and developers considering the construction of ADUs. In this section, we will explore the potential benefits ADUs offer, as well as the challenges that may arise during the process.

Benefits of ADUs

Increased Housing Options: ADUs provide additional housing options within existing residential properties, helping to address the growing demand for affordable housing in Washington DC.
Rental Income Potential: Homeowners can generate supplemental income by renting out the ADU, which can contribute to mortgage payments, property maintenance, or other expenses.
Multi-Generational Living: ADUs offer a solution for multi-generational living arrangements, allowing families to accommodate elderly parents or adult children while maintaining privacy and independence.
Aging in Place: ADUs can provide a suitable living space for aging homeowners, allowing them to downsize while remaining in their familiar neighborhoods.
Sustainable Development: ADUs promote sustainable development by utilizing existing infrastructure and reducing the need for new construction and urban sprawl.
Increased Property Value: Adding an ADU can enhance the value of a property, making it more attractive to potential buyers and increasing the overall marketability.

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Potential Challenges and Solutions

Cost of Construction: Building an ADU can involve significant upfront costs, including design and construction expenses. However, homeowners can explore financing options, such as loans or grants, to help offset these costs.
Regulatory Hurdles: Navigating the regulations, permits, and zoning requirements can be complex and time-consuming. Seeking guidance from professionals and consulting with local authorities can help homeowners overcome these challenges.
Neighborhood Resistance: Some communities may have concerns about the impact of ADUs on neighborhood aesthetics, parking, or density. Engaging in open communication with neighbors and addressing their concerns can help alleviate resistance.
Maintenance and Management: Renting out an ADU involves responsibilities such as property maintenance, finding tenants, and managing rental agreements. Homeowners may choose to hire property management services to handle these tasks.
Design and Space Constraints: Designing an ADU that meets the needs of occupants while adhering to size limitations and zoning regulations can be challenging. Engaging an experienced architect or designer can help optimize the use of space and ensure compliance with regulations.

By carefully considering the benefits and challenges associated with building ADUs in Washington DC, homeowners and developers can make informed decisions and maximize the potential of these additional dwelling units. With proper planning, communication, and adherence to regulations, ADUs can be a valuable addition to the housing landscape of the city.

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How to Build an ADU in Washington, DC

Building an Accessory Dwelling Unit (ADU) — or “Accessory Apartment,” as DC officially calls it — is a multi-step process that includes feasibility, permitting, and construction. Here's a breakdown of what to expect and how to get started the right way.

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Step 1: Check Feasibility

Before hiring anyone or drafting plans, assess whether your lot qualifies:

• Know your zoning – Use DC’s PropertyQuest to confirm your property’s zone. ADUs are allowed in most residential zones, but the rules differ.
• Confirm your lot size – You’ll need at least 1,200 sq ft of land area for a detached ADU.
• Check for overlays – Historic districts or special zones may have additional restrictions.

💡 Tip: Want help assessing your property? Gather ADU can run a feasibility check and zoning summary for you. Talk to our ADU experts

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Step 2: Schedule a PDRM (Preliminary Design Review Meeting)

The Department of Buildings offers two types of Preliminary Design Review Meetings (PDRMs):

• Zoning PDRM – Confirm use, location, and dimensional standards like setbacks and height.
• Plan Review PDRM – Review building plans and talk through code or structural requirements.

These one-on-one sessions are optional but highly recommended. They can save you time, money, and rework later.

Schedule directly via the DC DOB PDRM portal.

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Step 3: Design & Permitting

Once your feasibility is confirmed:

• Hire a design team – Work with a designer, architect, or ADU consultant to create site plans, floor plans, and elevations.
• Submit for permits – Apply for a building permit and include all construction documents. You may also need plumbing, electrical, and mechanical permits.
• Expect reviews – The Department of Buildings will review your application and may request revisions. This step includes zoning and code compliance checks.

Permit timing in DC can vary — sometimes weeks, sometimes months. Starting with a clean submittal helps.

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Step 4: Build Your ADU

Once you have permits in hand:

• Hire licensed contractors – Vet teams with DC experience. Make sure they’re bonded and familiar with city inspections.
• Track your timeline – ADUs can take 4–8 months to complete, depending on complexity and weather.
• Schedule inspections – You’ll need to pass inspections for foundation, framing, electrical, plumbing, and final occupancy.

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Step 5: Final Approvals

• Final Inspection – Once construction wraps, schedule a final walkthrough with DOB.
• Certificate of Occupancy (CO) – After passing your final inspection, you’ll receive your CO, which allows you to rent or occupy the space.
• Utility Setup & Landscaping – Set up electric/water service (if separate), and complete any remaining exterior work.

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Quick Tips for Homeowners

• Start early – The entire process, from zoning checks to final inspection, can take 6–12 months.
• You may only be allowed one ADU – and you might be required to live on-site, depending on your zone.
• Ask about pre-reviewed designs – If you’re in a rowhouse-heavy area, a repeatable plan might save time and reduce costs.

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Case Studies of Successful ADUs in Washington DC

Exploring case studies of successful Accessory Dwelling Units (ADUs) in Washington DC can provide valuable insights into the possibilities and impact of these additional dwelling units in the city. In this section, we will highlight a few notable examples of innovative ADU designs and how they are enhancing communities in Washington DC.

Innovative ADU Designs in DC

1. The Alley Flat: Located in the Shaw neighborhood, The Alley Flat is a unique ADU that was created by converting an existing garage into a modern and sustainable living space. It showcases how underutilized spaces, such as alleys and garages, can be transformed into functional and attractive ADUs.

2. The Basement Suite: In the Capitol Hill neighborhood, a property owner converted the basement of their rowhouse into a stylish and independent ADU. By utilizing the existing space, this ADU provides a separate and comfortable living area without altering the exterior aesthetics of the primary residence.

3. The Backyard Cottage: In the Brookland neighborhood, a homeowner constructed a detached backyard cottage as an ADU. This cottage features a compact yet well-designed layout, with a small kitchen, bathroom, and bedroom. It demonstrates how ADUs can be built in limited backyard spaces to provide additional housing options.

How ADUs are Enhancing Communities in DC

1. Increased Housing Density: ADUs contribute to increased housing density in neighborhoods without compromising the character and charm of existing residential areas. This allows more people to live in desirable neighborhoods, fostering diverse and vibrant communities.

2. Multi-Generational Living: ADUs provide an opportunity for multi-generational living, allowing families to stay together while maintaining privacy and independence. This promotes stronger family bonds and a sense of community within neighborhoods.

3. Support for Aging in Place: ADUs offer aging homeowners the ability to downsize while staying in their familiar neighborhoods. This allows them to maintain connections with their community and access necessary support systems.

4. Affordable Housing Solutions: ADUs can serve as affordable housing options, both for renters and homeowners seeking additional income. By providing more affordable choices, ADUs contribute to a more inclusive and diverse housing market.

5. Community Integration: ADUs can help foster community integration by adding new residents who can contribute to the local economy, support local businesses, and engage in neighborhood activities.

By studying successful case studies and understanding the positive impact of ADUs in Washington DC, homeowners, developers, and policymakers can gain inspiration and insights to further promote the construction and integration of ADUs in the city. These examples demonstrate the potential for ADUs to enhance housing options, create sustainable communities, and improve the overall livability of Washington DC.

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We get it — navigating the ADU process can feel overwhelming. Our mission at Gather is to simplify the process for homeowners who want to create flexible housing, care for family, or generate rental income responsibly.

If you're based in DC and considering an ADU, start by understanding your zone, your lot, and what you want to build. Then book a free ADU Chat with us — we’ll walk you through it all.

This isn’t just possible — it’s happening. And with the right guidance, your dream ADU can happen too.

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Talk to our ADU experts