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An Accessory Dwelling Unit (ADU) is a separate complete dwelling unit that is either attached to the existing single- family residence, wholly contained within the basement or attic, or in a separate stand-alone structure that is accessory to the primary use on the premises.

HB 1337: Prohibits a maximum ADU height of less than 24 feet, or no less the height limit that applies to the main house, if that limit is less than 24 feet (ensures that detached ADUs won't be taller than the main house). A height limit of 24 feet allows for a two-story detached ADU with a peaked roof.

An ADU costs approximately $150 to $300 per square foot on average, but some ADUs cost over $600 per square foot. The average-sized ADU is between 600 and 1,200 square feet, but your building's size may vary depending on personal preferences. ADU Size (sq.

1. Approval Process & Permitting Fees. One of the biggest challenges that homeowners face with building ADUs is government approval and permitting. Overall, 50% of homeowners found it difficult to build their ADUs to their city/county's development standards.

In Washington, you can build separate living spaces in single-family and lowrise zones, and in some cases, neighborhood or commercial zones. Requirements to construct an accessory dwelling unit in Washington include: You may construct up to two ADU's in SF5000, SF7200, and SF9600 zones.

You will need a few permits to construct your ADU in Washington. Whether you're building a unit attached to your home or a detached unit, you'll need a construction addition/alteration permit.

An ADU costs approximately $150 to $300 per square foot on average, but some ADUs cost over $600 per square foot. The average-sized ADU is between 600 and 1,200 square feet, but your building's size may vary depending on personal preferences. ADU Size (sq.

(1) "Accessory dwelling unit" means a dwelling unit located on the same lot as a single-family housing unit, duplex, triplex, townhome, or other housing unit.