Washington Passes Law to Boost Affordable 'Kit Homes'

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Washington Governor Bob Ferguson has signed a new law that will make it easier to build small 'kit homes' and backyard units across the state. The measure directs the state Building Code Council to develop rules specifically for kit homes 800 square feet or smaller, with the goal of reducing costs and simplifying the construction process for these types of affordable housing options.

Why it matters

Washington is facing a severe housing shortage, with state officials estimating the need for over 1 million additional homes by 2044. This new law is intended to provide a more affordable and accessible path for homeowners to build smaller prefab homes and accessory dwelling units on their property, helping to address the state's affordable housing crisis.

The details

The new law, Engrossed Substitute Senate Bill 5552, was championed by Sen. Jeff Wilson of the 19th Legislative District. It directs the Washington State Building Code Council to develop standardized building code rules for kit homes 800 square feet or smaller by March 31, 2027. This is expected to allow kit home plans to be approved once at the state level, rather than requiring separate design reviews for each individual project. Kit homes typically include precut lumber and other materials delivered as a package that can be assembled on site, often using prefabricated wall and roof panels to speed up construction. Some basic kit home models can cost less than $10,000.

• Gov. Bob Ferguson signed the bill into law over the weekend.
• The state Building Code Council must complete rulemaking for kit-home construction by March 31, 2027.

What they’re saying

What’s next

The Washington State Building Code Council has until March 31, 2027 to complete the rulemaking process for the new kit home construction standards.