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Zena Heywood
Bellevue, WA · Attached ADU
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HB 1337 explained, in plain English
The 2023 Washington state law that rewrote ADU rules in Seattle, Bellevue, Kirkland, Redmond, Mercer Island, Sammamish, Issaquah, and Newcastle. What it changed, where it applies, and what your lot now allows. Written by MNBE founder Aharon Ben Elisha.
Signed May 2023
RCW 36.70A.681
2 ADUs per lot mandated
The Bill
What HB 1337 actually is.
HB 1337 is a Washington state law passed during the 2023 legislative session and signed by the Governor in May 2023. It removes local government barriers to building Accessory Dwelling Units across the state. The enforceable text lives in RCW 36.70A.681, a section of the Growth Management Act that binds every city of 25,000 people or more, including Seattle, Bellevue, Kirkland, Redmond, Mercer Island, Sammamish, Issaquah, and Newcastle.
It is a preemption statute. The state legislature explicitly overrode any conflicting city or county code. Before HB 1337, ADU rules were almost entirely local. After HB 1337, the floor is the same statewide: a city can be more permissive, but no city can be more restrictive than the statutory minimums on the items the law covers. The practical effect is that thousands of Seattle and Eastside lots that were unbuildable under prior codes are now permittable. Confirming what it allows on your land is the first step in a feasibility study.
Run my lot through HB 1337
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HB 1337 · 2023 WA Law
The six changes, by the numbers.
A 2023 state preemption statute that reset the floor on ADU rules across Seattle and the Eastside. Confirm it on your lot with a feasibility study →
2
ADUs per lot
Cities of 25,000+ must permit at least two ADUs on every residential lot.
25,000population floor
Who it binds
Every WA city of 25,000 people or more under the Growth Management Act.
½mile of transit
No added parking
No off street parking can be required within half a mile of major transit.
No
Owner occupancy
Cities can no longer force the owner to live on the property.
What HB 1337 does not change.
A zoning law, not a build code.
HB 1337 expanded zoning rights, not construction or environmental rules. The Washington State Energy Code, fire, plumbing, mechanical, and the International Residential Code all still apply in full, and an ADU must meet the same standards as any habitable structure. Knowing which of these still bind your lot is exactly what a feasibility study and a zoning and setback analysis are for.
Still in force after HB 1337
- Building, energy, fire, and plumbing codes
- Critical area review for slopes, wetlands, and streams
- Reasonable height and lot coverage caps
- Design review in landmark and overlay districts
- Water, sewer, and stormwater capacity standards
Your Lot
How we run your specific lot through HB 1337.
The state floor is the same everywhere. Your buildable footprint is not. Here is how we translate the law into a written answer for your address.
01
Confirm jurisdiction
We confirm your lot sits in a city of 25,000 or more inside an Urban Growth Area, so HB 1337 applies.
State floor
02
Apply the six changes
We measure your zone against the mandates: two ADUs, no owner occupancy, no parking near transit, capped setbacks and lot minimums.
Zoning rights
03
Layer the limits
We add back height, lot coverage, setbacks, critical areas, and utility capacity to find your real footprint.
Constraints
04
Review covenants
If an HOA covenant exists, we test its old ADU ban against amended RCW 64.38 to see whether it still holds.
HOA check
05
Written feasibility
You get a written feasibility study stating, in plain language, exactly what your lot allows.
In writing
Reviews
What Seattle homeowners say about building with MNBE.
Verified five star reviews from owners we guided through ADU feasibility, permitting, and construction.
"We hired MNBE for a full renovation of our 100 year old home and the results exceeded expectations, structural upgrades, new insulation, a luxury bathroom, a high end kitchen, a new roof and mini split AC."
Dave Gierok
Sammamish, WA · Whole home renovation
"We hired MNBE for a major exterior renovation: a 900 sq ft custom deck with metal railings, full exterior painting and new siding. From start to finish the experience was exceptional, responsive, meticulous and patient."
Santosh S.
Redmond, WA · Deck & exterior
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FAQs · HB 1337
HB 1337 questions Seattle homeowners ask before they call us.
The legal text is dense. The practical answers are not. If yours is not here, call us. Two minutes on the phone usually clears it up.
HB 1337 is a 2023 Washington state law, codified as RCW 36.70A.681, that overrides local zoning to expand ADU rights. In cities of 25,000 or more, every residential lot must allow at least two ADUs, owner occupancy can't be required, parking minimums near transit are eliminated, and minimum lot sizes are capped. Thousands of previously unbuildable Seattle and Eastside lots are now permittable.
HB 1337 was signed in May 2023, and cities had until July 1, 2025, or six months after their next required Comprehensive Plan update, whichever was later, to comply. Seattle, Bellevue, Kirkland, Redmond, Mercer Island, Sammamish, and Issaquah have all updated their codes. Cities that missed the deadline must apply state default rules directly, so the law is enforceable today.
If your lot is zoned residential and sits inside an Urban Growth Area of a county with a city of 25,000 or more, HB 1337 applies. That covers virtually all of King County, most of Snohomish County, and urbanized Pierce County. It does not apply to rural residential or resource land zoning, tribal land, or cities under 25,000 with no qualifying neighbor.
Yes, in nearly every Seattle and Eastside city. HB 1337 mandates at least two ADUs per residential lot in any combination: detached plus attached, two detached, or basement plus detached. Seattle and Bellevue already allowed two; Mercer Island and Issaquah expanded from one. Floor area, height, and lot coverage caps still apply, so the legal allowance isn't always a buildable allowance.
Largely yes. Cities under HB 1337 cannot require off street parking for an ADU within one half mile of a major transit stop, and farther out they can require at most one space per ADU, only if justified. Most residential zones in Seattle, Bellevue, Kirkland, and Redmond fall within transit walking distance, so most MNBE projects need zero parking spaces.
From here, the natural next steps are a feasibility study, a zoning and setback analysis, or a faster path with pre-approved DADU plans. Start at the permits and design hub.
View all FAQs
Contact Us · Free Estimate
Tell us about your project.
We'll run your address through HB 1337 and get back to you within one business day with a clear next step.
Contact information
Thank you for considering MNBE. Tell us your address and we will tell you, in writing, what HB 1337 allows on your lot. We respond within one business day, Monday through Saturday.
(206) 637 0044
info@mnbe-wa.com
2014 Fairview Ave Unit 2308, Seattle, WA 98121