recent adu & dadu projects

In the greater Seattle area, the typical cost to build an ADU is approximately $350 to $450 per square foot. This price includes construction labor and rough materials — framing, structural work, and core building systems. It does not include finish materials like flooring, paint, kitchen and bathroom materials, fixtures, or appliances. The total cost depends on size, site conditions, permit requirements, and the level of finishes chosen.

An ADU (Accessory Dwelling Unit) is a secondary living unit on the same property as the main house — it can be attached, built inside the home (such as a basement unit), or detached. A DADU (Detached Accessory Dwelling Unit) is a specific type of ADU that is completely separate from the primary residence, typically built as a standalone backyard cottage or small independent structure with no shared walls.

In the Seattle area, building a backyard cottage typically takes about 8 to 14 months from start to finish. This includes permitting, site preparation, construction, and final inspections. For a standard DADU around 1,000−1,500 sq ft, the construction timeline is usually around 8 months. A larger project of around 3,000−3,500 square feet can take closer to 14 months, because it would need to be permitted not as a DADU, but more like a townhouse-type structure. The permitting process for that typically takes longer, and the construction itself also takes additional time, depending on design complexity, site conditions, and city permit review timelines.

Yes — in Seattle you can legally rent out your ADU (long-term or short-term), as long as it is properly permitted and registered. ADUs are allowed as rental units under Seattle zoning and building codes. There is no owner-occupancy requirement, meaning you do not need to live in the main house or the ADU in order to rent it out.

Yes — building an ADU typically increases property value because it adds additional livable square footage, creates a rental income stream, and makes the property more attractive to buyers looking for multi-generational housing or investment opportunities. In high-demand markets like Seattle, an ADU can significantly improve resale value by turning a single-family lot into a more flexible, income-producing property.

Yes — we manage the full permitting and city approval process for ADU, DADU, and extension projects. This includes preparing all required documentation, coordinating with architects and engineers, submitting plans to the City of Seattle, and guiding the project through plan review, inspections, and final approval to ensure full compliance with building codes and regulations.

There are several financing options commonly used for ADU and DADU projects in Seattle — including home equity loans (HELOC), cash-out refinancing, and construction loans. The right option depends on your current equity, credit profile, and how you plan to use the unit. We work with trusted local lenders who specialize in ADU and home improvement financing and can connect you with the right person based on your situation. Just bring it up during your free consultation and we'll point you in the right direction.

Yes — in many cases, you can legally convert an existing garage into an ADU in Seattle, as long as the structure meets current zoning, building code, and safety requirements. The garage must be permitted, upgraded for insulation, plumbing, electrical, and egress, and approved through the city's plan review and inspection process. Feasibility depends on property layout, utility access, and Seattle ADU regulations. We assess this during your free consultation.

Under Seattle's 2025 zoning updates (HB 1337 and HB 1110 compliance), you can build up to two ADUs per lot that contains a principal dwelling unit. Both can be detached (two DADUs), or any combination of attached and detached. Some lots near major transit stops can accommodate up to 6 total units. Two DADUs can even be located in the same structure. ADUs count toward overall density limits.

Standard: 5-foot setback from side and rear property lines. If your property borders a back alley, you can build with zero setback on the alley side. Front setbacks follow standard zoning rules. When a DADU exceeds 18 feet in height, Seattle requires increased setbacks from property lines. These requirements apply across all NR zones (NR1, NR2, NR3, and RSL zones).

No. Seattle eliminated off-street parking requirements for ADUs in both the 2019 reforms and 2025 updates. You can choose to include parking, but the code doesn't require it. This reduces construction costs, makes projects feasible on smaller lots, and promotes transit-oriented development.

Each ADU can be up to 1,000 sq ft of gross floor area in most NR zones. The actual buildable size also depends on your lot's Floor Area Ratio (FAR up to 1.2 depending on zone) and lot coverage limits. Conversions of existing structures (basements, garages) may exceed the 1,000 sq ft limit. Minimum lot sizes no longer apply for ADUs.

Yes. Under the 2025 rules, DADUs can be up to 32 feet tall in Neighborhood Residential zones and up to 40 feet in other areas. The ridge of a pitched roof can extend an additional 5 feet above the height limit within a 4:12 sloped envelope. This means two-story DADUs are now fully possible and increasingly popular for maximizing space on smaller lots.