English basement accessory apartment in DC by Daniel Warwick.

“Where do I even start?!” is the first question I hear from people when it comes to building accessory apartments, also known as Additional Dwelling Units or ADUs. Here's a step-by-step list outlining how to bring your accessory apartment from dream to reality.

Step 1: Is an accessory apartment right for you?

If you build an accessory apartment, that most likely means you will share your property with another family. You will also lose some of the space you already have, maybe the basement or a portion of the back yard. It also means a financial commitment that you should evaluate.

Of course, an accessory apartment also adds value to your hou se and will provide you with supplemental income. Some online tools allow you to find how much your house is worth now and calculate how much rent you may obtain if you lease an accessory apartment.

If you live in the District, another useful tool is DC Zoning’s website. It allows you to verify if your property is in a zone that allows additional dwelling units, among other details.

Step 2: Call an expert

Once you've decided to move forward, architects, builders, and designers will be ready to discuss the following:

  • What project do you want? Is it an accessory apartment or an addition?
  • Where in the lot will the accessory apartment be located? Is it ideal? Is that location the right decision for existing structural/financial/infrastructure conditions?
  • Who is the accessory apartment for? Will it be for rent, for a relative, or for the homeowner? Will the user need assistance due to age or disability? Will the user change over time?
  • How will this affect the existing conditions of the building? What are you losing or gaining by implementing an accessory apartment?
  • How much will the project cost? How much is the building now? How can we make the project a better financial decision?
  • When will this process be complete? From design to construction, can it be phased?

During the call, the architect will be able to share their experience with accessory apartments, provide you with resources to investigate, and offer other suggestions. The architect may also have some initial thoughts on how to address problematic areas.

During the early discussions with the architect, you can ask for a sample of work submitted and approved by the local building agency. This should give you an idea of the scope of work you should expect at this point. You can also check the architect’s license in the American Institute of Architects (AIA) website, as well as their portfolio and references of previous clients.

Step 3: Have an expert visit your house

Architects and general contractors (GCs) are experienced professionals to look at a structure and note the benefits and impediments of a certain ideas. They will notice existing structural and infrastructure conditions, potential alterations, and cost implications of each decision. During this meeting, you will be able to discuss the three big answers of any design project: the scope, timeline, and budget. You will also explore design options and your original concept.

The architect or GC will also suggest changes that could add to the value of your own home, but aren't about building the accessory apartment. For example, if you are closing a stair to accommodate an accessory apartment in the basement, adding a powder room in the main floor may be an improvement to the main residence. The same goes for relocation of mechanical, plumbing, and laundry equipment.

During the interview process, ask your architect how the different steps of the project will be coordinated. Make sure the architect describes the design process and shows samples of what to expect after each phase has been completed.

Step 4: Have a plan to document the design

Once you have met with a professional, discuss their capacity to develop design and permit drawings that must be filed for a building permit. Architects hold professional licenses that allow them to complete both processes, while other designers just complete one portion of the work. Whoever you hire to do this portion of the work, design, and documentation, make sure they commit to the whole process as detailed below:

  • Design
  • Permit documents
  • Addressing Department of Consumer and Regulatory Affairs (DCRA) comments
  • Permit assistance

You can also hire the architect to assist during construction. They should be able to provide a descriptive proposal detailing the scope of work, fee, and services included.

Because of the complexity of accessory apartments in an urban setting, the project requires a multi-disciplinary approach. As small as they are, they contain a complex system of structural, mechanical and electrical items, among many others. Whoever you hire to design and document your accessory apartment, make sure the professional has a team in place to develop the following sheets:

  • Architectural
  • Plumbing
  • Electrical
  • Mechanical
  • Structure
  • Fire protection

Step 5: File for permits

Once you have the complete design, you will need the following drawings and documents to file with DCRA. Because of the complexity of an additional dwelling unit, you will need to use DCRA’s ProjectDox system (other jurisdictions will have their own requirements). Accessory apartment are not accepted via the Homeowner Center.

To file for permit, you will need the following documents:

Step 6: Wait for comments and address them

DCRA will have questions about construction details, performance, and code compliance issues. The building code alone is 1,700 pages that cover the six disciplines listed above. Because every additional dwelling unit is the result of a series of design decisions, the potential for clarification is very long. (Granted, the more experienced the architect, the fewer comments you tend to get.)

So how does DCRA issue comments?

DCRA permitting reviews are by discipline. Each discipline reviews the set independently and you can follow their progress by clicking on the ProjectDox website and the Q-tracker application. You can only provide answers after all disciplines have been approved and you will need to supply the answers in drawing and written form.

Based on experience in my own firm, the average approval time for an additional dwelling unit ranges from four to six months.

Step 7: Bids and contractors

During the time it takes to approve the building set you may want use this period to interview general contractors, compare bids and refine aesthetic choice. The permit set will be fundamental at comparing apples-to-apples.

All the GCs will be looking at the same building, the same materials and choices. A portion of the project will be estimated in bulk (for example, drywall) and others by unit (such as cost per square footage of tile). General Contractors in DC must have insurance and bond. You can check the status of their license on the DCRA website.

Step 8: Permit and building

Once the permit has been approved and you have a signed contract with the GC, GREAT! … you can start construction. The construction time varies greatly depending on the complexity of the project. The GC should be able to estimate a reasonable period of construction during the bidding process.

In my experience, the approval time has been between four and six months. During the construction there will be series of inspections by DCRA personnel to make sure that the building is being completed by the building application. Depending on the agreement you have with the architect, they may be able to assist on the construction process as well.

More resources:

There are a variety of groups and associations that are assist homeowners with creating accessory apartments. Here are more resources, listservs, and professional associations:

Argentina-born Ileana Schinder is a licensed architect. She holds a B.Arch in Architecture from Universidad Nacional de Córdoba (Argentina) and an MA in Public Communication from American University (Washington, DC). Ileana has nurtured her passion for architecture since first hearing the click of LEGO bricks at the age of four. She lives in Washington, DC with her family and Cecilia, the dog.