Two Washington State laws — House Bill 1110 and House Bill 1337 — are reshaping what homeowners can build on their own lots. Together they expand the right to add middle housing and accessory dwelling units (ADUs) in neighborhoods that were previously limited to single detached homes, unlocking new housing opportunities across the state.
HB 1110 requires many cities to allow middle housing — duplexes, triplexes, and similar building types — on lots traditionally zoned for single-family use. HB 1337 expands the right to build accessory dwelling units (ADUs) and detached accessory dwelling units (DADUs), easing the path for homeowners to add a second home on their property.
Where Civil Engineering Comes In
New zoning rights are only the first step. Adding a unit or splitting a lot still means meeting your jurisdiction's requirements for stormwater, drainage, grading, access, and utilities — and on built-out residential lots, those requirements are often the deciding factor in whether a project pencils out.
AXE helps homeowners and small developers turn these new opportunities into permitted, buildable projects: confirming what your lot can support, designing the site civil and drainage, and carrying the plan through review.
Thinking about an ADU, a DADU, or a middle-housing project on your property? Reach out and we'll walk you through what it takes.