ADU Construction Services in Seattle
Harjo Construction is a Seattle-based contractor specializing in the design and construction of accessory dwelling units (ADUs). With over 300 projects completed since 2010, they bring hands-on experience to attached accessory dwelling units (AADUs) and detached accessory dwelling units (DADUs) across the Seattle area.
Many Seattle homeowners are exploring ADU options in response to updated city housing rules. The City of Seattle has approved legislation making it easier for homeowners to build an attached or detached accessory dwelling unit on their property. These changes were introduced to increase housing density and improve the availability of affordable housing, opening up new possibilities for property owners.
Types of ADUs Harjo Construction Builds
Attached Accessory Dwelling Units (AADUs) are self-contained living spaces connected to the main home. These are often built within a basement or as an added story. Sometimes referred to as mother-in-law suites or in-law suites, they typically include a private bathroom, kitchen, and separate entrance. An AADU can be a practical solution for multigenerational households, allowing family members to live nearby while maintaining their own independence.
Detached Accessory Dwelling Units (DADUs) — also known as backyard cottages or granny flats — are standalone structures separate from the main house. A typical DADU in Seattle ranges from 800 to 1,000 square feet and can include a kitchen, bathroom, bedroom, and laundry. As an ADU builder, Harjo Construction handles these projects from planning through completion.
In addition to providing housing for family members, both AADUs and DADUs can generate rental income, either through long-term leasing or short-term rental platforms. The return on investment will vary depending on the Seattle neighborhood and the specifics of the project.
Common Questions About Seattle ADUs
For homeowners considering an ADU, here are some practical details relevant to Seattle properties:
- Lot size requirement: A minimum lot size of 3,200 square feet is needed to add a DADU.
- Maximum size: Both AADUs and DADUs are limited to 1,000 square feet in Seattle.
- Permitting timeline: The permitting process typically takes four to six months.
- Construction timeline: Building an AADU or DADU generally takes four to six months, depending on factors such as weather and material availability.
- Cost of a basement AADU: Average costs range from $275,000 to $475,000, with potential increases based on design and material choices.
- Cost of a DADU: Average costs range from $350,000 to $650,000, again depending on design and materials.
- Owner-occupancy: The City of Seattle has removed the owner-occupancy requirement, allowing non-resident owners to build ADUs for rental purposes.
- Off-street parking: No additional parking is required, but existing required spaces cannot be removed unless replaced on the lot.
Harjo Construction works with both their in-house design team and with homeowners' chosen architects or designers. They offer virtual consultations as well as on-site property visits to help assess feasibility and guide preconstruction planning. Whether the project involves a garage conversion, a basement AADU, or a new detached ADU builder engagement, they aim to walk clients through the full process from start to finish.
Homeowners interested in checking lot eligibility can use the ADUniverse tool, which allows address-based searches to determine what can be built on a given Seattle property.
