Basement / Junior ADU in Seattle, Washington
Verified basement / junior adu businesses in Seattle, WA
Frequently Asked Questions — ADU Builders in Seattle
How much does it cost to hire an ADU builder in Seattle?
ADU construction costs in Seattle, Washington vary widely depending on size, type, and site conditions. Detached ADUs typically range from $150,000–$400,000+, while garage conversions and attached ADUs can be more affordable. Contact multiple builders in Seattle to get accurate quotes for your specific project.
How long does it take to build an ADU in Seattle?
In Seattle, the ADU construction timeline typically ranges from 6 to 18 months from permit application to move-in. Permitting alone can take 2–6 months depending on Washington local regulations. Prefab and modular ADUs often have faster timelines than site-built units.
Do I need a permit to build an ADU in Seattle?
Yes, a building permit is required for ADU construction in Seattle, Washington. Your ADU builder will typically handle the permit application as part of their service. Washington has adopted streamlined ADU permitting laws in recent years, which may reduce wait times.
What types of ADUs can be built in Seattle?
Common ADU types in Seattle include detached ADUs (backyard cottages), attached ADUs, garage conversions, basement conversions, and prefab/modular ADUs. The best type for your property depends on lot size, zoning, and budget. A local Seattle ADU builder can advise on what's allowed on your specific parcel.