Accessory Dwelling Unit (ADU)

An Accessory Dwelling Unit (ADU) is a secondary housing unit constructed on the same property as the primary home. The unit can be attached to the main house or detached. ADUs can also be referred to as mother-in-law suites, garden suites, backyard cottages, granny flats, laneway houses and carriage houses.


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Following the adoption of new zoning regulations in 2016, ADUs have become more popular in the Washington, DC area. However, homeowners should not confuse zoning regulations for building codes. While codes provide guidelines on how to build your structure, zoning regulations tell you how large you can build and what part of your property you can use for your unit.

Types of Accessory Dwelling Units

ADUs can be classified into three categories:

  • Detached: Detached structures are standalone units constructed in your backyard or side yard. They resemble carriage houses, and they have a separate entrance from the main house. The main benefit of this type of ADU is that tenants may come and leave as they please without interrupting occupants of the main house.
  • Attached internal apartment: An attached internal apartment is part of the primary structure. This ADU is usually a finished basement or attic that the homeowner has remodeled into an apartment.
  • Attached external apartment: An attached external apartment shares at least one wall with the primary unit. It has a separate entrance, and the unit does not share an internal connection with the primary house.

Why Should I Build an Accessory Dwelling Unit?

Whether you need more space to accommodate your senior loved ones, or you want to create additional income from short-term rentals, building an ADU is a smart option to consider. Reasons why you should build an accessory dwelling unit on your property include:

  • Flexibility: ADUs provide extra space that can help address your lifestyle changes and the growing needs of your family. You can use the newly designed space to accommodate older kids or elderly loved ones, ensuring more privacy for everyone.
  • Sustainability: Building a new home from scratch requires plenty of resources. ADUs do not require as many resources. In most cases, ADUs draw utilities from the main house, saving on energy consumption and new installations.
  • Rental income: If you want to make a little extra income, building an ADU is the way to go. These units can provide long-term or short-term rental income, depending on your preferences.

The cost of building an accessory dwelling unit depends on several factors, such as the type of unit, size of the structure, location, plumbing work and mechanical connections. In addition, the accessory dwelling unit contractor you hire will determine whether you’ll get real value for your money.

Contact Ideal Construction & Remodeling for ADUs in McLean and DC

At Ideal Construction & Remodeling, we’re the experts when it comes to building high-quality accessory dwelling units. We have vast experience in constructing all types of homes and structures. Trust our team to take care of the entire process. Get started today by contacting us for your free in-home consultation.

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2017 through 2021 Best of Houzz Service Award

2019 through 2021 Best of Houzz Design Award

Arlington County Green Home Choice Award

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