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Home Additions in Seattle, WA

When you need a reliable source for home additions in Seattle, WA, turn to the experts at ACS Seattle. Attached or detached accessory dwelling units (ADU/DADU) dramatically increase the property value of a home while also adding ample space for you to live and work. ADUs also offer potential tax advantages compared to bedroom or basement home offices. Some clients even transform their former garages into profitable apartment rental units, vacation rental spaces, yoga studios, recording studios, production or repair workshops, and more.

Our remodeling contractors would be happy to provide a free verbal estimate and honest assessment on-site. We can give you great home addition ideas so you don't feel like you're wasting your money. Come to us to provide you with the best solution possible while still protecting your investment. Contact us today to discuss how we can help you with your home additions!

Accessory Dwelling Unit

An accessory dwelling unit is described as a legally permitted dwelling unit that is attached to a single-family house but has a separate entrance. These units typically have their own kitchens, bathrooms, and living areas. ADUs can be renovated from an existing part of the home or built onto an existing part of the home. They might also serve a special purpose as a commercial yoga or fitness studio, recording studio, or rehearsal space.

Our experienced team would be happy to create such a dwelling or building an addition to the house for you. In Seattle, ADUs are limited to 1000 square feet when attached to a single-family home — or 650 square feet when attached to a townhome or row-house. Off-the-street parking is required for ADUs except in certain low-rise zones or urban villages. Call today to put us to work!

Detached Accessory Dwelling Unit

Often referred to as a backyard cottage, these home addition units can be placed anywhere on the property that is legally permitted. In most cases, additional dwelling units are built from a renovated garage or are built in the former location of a detached garage. They're perfect for a wide range of uses, and we can't wait to get to work on yours.


  • Minimum lot size for a DADU is 4000 square feet.
  • Gross floor area for a DADU is 800 square feet for single-family homes and 650 square feet for townhomes and row-houses.
  • Off-the-street parking is required for DADUs, except in certain low-rise zones or urban villages.


Permits can be confusing, but you don't have to let them stress you out. Our remodeling contractors at ACS Seattle will happily manage the permitting process, allowing you to determine which type of unit makes the most sense for you.

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