If you’ve ever considered building a backyard cottage or adding a small rental unit to your property, the door just opened a little wider. A new Seattle ordinance will allow all homeowners to build not just one, but two accessory dwelling units on a single-family lot. That means more flexibility for homeowners, more options for renters, and a big shift in how neighborhoods might grow.
What Changed?
Before, homeowners could add one detached unit, often called a DADU or backyard cottage, and one attached unit, such as a basement apartment. Now, you’re allowed two in total, and they can both be detached.
Picture this: a main house in front, with two compact, livable units tucked into the backyard. Whether used for family, rental income, or a private studio, it’s a significant increase in what’s possible on a standard residential lot.
Along with the change in number, the ordinance loosens some of the old restrictions. Here’s what’s now allowed:
- Up to 1,000 square feet per ADU
- Heights up to 32 feet in many zones, enough for two-story structures
- Reduced setbacks that match what’s already allowed for main houses
- No more requirements for extra parking or minimum lot sizes
In short, it’s easier to build, and there’s more room to design something that actually works.
Why it Happened
This update comes from a new state law, HB 1337, that required cities to expand access to ADUs. The goal was to create more housing in existing neighborhoods, without requiring full-scale redevelopment.
Seattle responded with Ordinance 127211, which officially went into effect on July 15, 2025. It also aligns with broader efforts across the city to support “middle housing,” like duplexes and courtyard clusters.
The idea is simple: give homeowners more flexibility, and create more places to live in neighborhoods that have been zoned for single-family use for decades.
What is means for your neighborhood
Most lots won’t see major changes overnight. Building an ADU still takes time, planning, and money. But over the next few years, you may start to see more backyard homes popping up. Think compact cottages, alley-facing lofts, or studio apartments above garages. For some homeowners, this opens the door to multi-generational living. For others, it’s a chance to generate rental income or downsize while staying put. And for renters, it could mean more housing options in quieter, residential areas.
Wondering if it’s a fit?
We’re already hearing from people who are curious – people with growing families, aging parents, or a strong interest in creating long-term flexibility on their property. Every lot is different, and permitting still requires a thoughtful approach. But these new rules make it easier to get creative and use your land well. If you’re thinking about building, we’re happy to help you explore what’s possible.
To see how this fits into the city’s broader housing goals, you can explore the One Seattle Plan, which outlines where and how zoning is evolving across Seattle.