Washington's Middle Housing Law (HB 1110): What It Means for Seattle Homeowners
Washington's HB 1110, often called the middle housing law, changes what can be built on residential lots across the state's larger cities, including Seattle. For homeowners, the big question is simple: could your lot be worth more, and how might a fourplex or townhome project next door affect your street? TC Wu explains the basics and what to consider before you sell, rebuild, or buy. Zoning rules are detailed and still being implemented, so confirm specifics for your parcel with the City of Seattle.
What Homeowners Should Know
Four ways middle housing may touch your property or your next purchase.
What HB 1110 Actually Requires
HB 1110 directs Washington's larger cities to allow middle housing, meaning duplexes, triplexes, fourplexes, townhomes, and similar small-scale homes, in areas that were previously limited to single-family houses. In cities over 75,000 people, such as Seattle, the law calls for at least four units per lot, and up to six units on lots near major transit or when some units are affordable. Local governments set many details, including design review, so the rules on your block can differ from the headline numbers.
Your Lot May Be Worth More Than You Think
Where zoning allows more homes, some lots become more valuable to builders and investors than the existing house is to a typical owner-occupant, especially older, smaller homes on larger lots near transit. That does not mean every property will sell for a premium, and results vary by lot size, shape, slope, utilities, and location. A professional valuation that considers both the home as it stands and the lot's development potential is the best way to understand your options.
What New Neighbors Could Mean for Your Street
Middle housing tends to arrive gradually, one lot at a time, rather than overnight. Over time you may see more townhomes and small multiplexes, more people using local shops and transit, and changes to street parking. Cities generally apply design review, setbacks, and tree-canopy rules, and the law limits how much parking can be required near transit. Some owners welcome the added options and others worry about density, so setting expectations early helps.
Opportunities for Buyers and Investors
More small-scale housing can increase the variety of homes available, including townhomes that may be sold individually, which can open doors for first-time buyers. Investors and owner-builders may also find new ways to add units, such as building on a larger lot or converting an existing home. Costs for construction, financing, and permitting still matter a great deal, so any project needs careful numbers before purchase.
"I've watched Seattle neighborhoods change many times over the decades. Zoning changes create opportunity, but only for owners who understand their lot and their numbers. Look before you leap, and look again."— TC Wu, WPI Real Estate | Top Seattle Realtor
Middle Housing Rules by City Size
General framework under HB 1110. Local rules and later amendments may differ, so verify with your city.
| City Size | Baseline Requirement | Extra Allowance |
|---|---|---|
| Over 75,000 residents (e.g., Seattle) | At least 4 units per lot | Up to 6 near major transit or with affordable units |
| 25,000 – 75,000 residents | At least 2 units per lot | Up to 4 near major transit or with an affordable unit |
| Under 25,000 (inside a large city’s urban growth area) | At least 2 units per lot | Varies by city |
Your Middle Housing Action Checklist
Five steps for Seattle owners and buyers.
Confirm Your Zoning and Lot Details
Check zoning, lot size, slope, and any critical-area or tree rules with the City of Seattle.
Get a Dual-Value Opinion
Ask an experienced agent to compare your home’s value as-is with its potential as a development site.
Check Private Restrictions
Review deed covenants and any HOA rules, which may affect what you can build or sell.
Run the Full Numbers
If you are considering building, price permits, construction, financing, and timelines before deciding.
Talk to a Local Expert Before You List
A realtor who knows your neighborhood can help you decide whether to sell now, wait, or build.
Frequently Asked Questions
Common questions answered by TC Wu. Zoning rules change, so verify with the City of Seattle.
Find Out What Your Lot Could Be Worth
Let TC Wu help you understand how Washington's zoning changes may affect your Seattle property.
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