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Types of ADUS

Several options exist when adding an accessory dwelling unit (ADU) to your property. In this post, we'll explore the three main types of ADUs: Attached, Detached, and Conversion. Then, we'll outline the benefits and disadvantages of each type to help you make an informed decision.

Attached unit over the garage


Attaching a new addition to the home can be an effective way to create an ADU that is separate from the primary living areas of the home. This type of ADU can add square footage to the home, maximize outdoor space and provide a separate entrance for the occupants.


  • It can create a natural extension to the home, blending in with the existing design and maximizing outdoor space - especially if the outdoor space is limited.

  • It can be a good option if you're looking to add square footage creatively and separate the new living area from the existing one.

  • It can add value to your home and increase its resale value.

  • If your existing home is a 2-story home, you can build a 2-story addition, matching the existing height of the main home


  • Depending on the condition of the home and where the addition is taking place, it may require some reconfiguration of the interior space (moving existing windows, doors or creating a new roofline), which can add additional costs to the project. There will be some additional costs for "as-built" drawings to show the existing structure too.

  • Less privacy sometimes, especially if the new living area extends from your home.

  • Greater disruption to the owner while construction is taking place in the main home

  • If you're adding an addition that connects to an existing room, it could disrupt the flow of the house and affect its overall design.

New detached unit in the rear yard


Constructing a new, free-standing ADU can provide the most flexibility regarding size, configuration, and amenities. This type of ADU can be designed to blend seamlessly with the primary home or as a standalone structure with its own unique look and entrance.


  • You have the most design freedom since you're starting from scratch.

  • You can create a larger living space with more amenities, such as a full kitchen, separate bedrooms, or a private outdoor area.

  • It’s a great option if you're looking to create a separate living area that's not connected to your existing house.

  • It allows for different building approaches - such as prefab or modular units and pre-approved designs (if jurisdictions have these available)


  • It is more expensive than homeowners may think since you're building a new structure from the ground up.

  • It could encroach on outdoor space and affect the overall aesthetic of your property if your yard is small.

  • Depending on your area's location and zoning laws, you may face additional permitting and approval processes.

Conversion of an old carriage house


Converting an existing space, such as a garage, a basement or underused room in the home, into an ADU can be a cost-effective way to add living space to your property. This type of ADU can be designed to blend seamlessly with the existing home and often requires less construction than the other two types.


  • The existing structure provides a head start, making it less expensive than starting from scratch.

  • It can be a great way to repurpose an underused space and add value to your property.

  • It can help keep the backyard size intact and preserve the outdoor space.


  • Depending on the condition of the home or garage, it could trigger additional construction projects to bring the structure up to code or make it suitable for habitation.

  • Less privacy if you are sharing interior walls/ceilings.

  • Greater disruption to the owner while construction is taking place in the main home.


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