Granny Flat Prices in Seattle

Granny flat prices in Seattle start from $4,500/job. A 1-bedroom granny flat costs $99,000 on average. Prices do not include sales tax. ADU regulations vary significantly by state and city. California, Oregon, and Washington have the most permissive ADU laws. Allow 4–9 months from permit to completion.

The best granny flat type depends on your budget, lot size, and intended use. Kit/prefab options in Seattle start from $45,000 for a 1-bedroom. For rental income, a 1-bedroom or 2-bedroom with standard finishes offers the best return on investment. For family use, consider accessibility features and a more generous layout.

A standard granny flat in Seattle takes 12–20 weeks from slab to handover. A 2-bedroom build averages $144,000 and takes 16–20 weeks. Kit/prefab builds can be completed in 8–12 weeks. Council approval adds 2–24 weeks depending on the pathway.

Yes — all granny flats in Seattle require building or planning approval. Your builder or certifier will advise on whether you can use a fast-track approval pathway or need a full development application. The approval process, costs, and timeline vary by council area.