What Is HB 1337?
House Bill 1337 is Washington State legislation that fundamentally changed the rules around accessory dwelling units — including DADUs. Passed to address the state’s housing shortage, HB 1337 removed many of the barriers that previously made building a DADU difficult, expensive, or impossible in many jurisdictions.
If you looked into building a DADU a few years ago and hit a wall of restrictions, it’s time to look again. The landscape has changed dramatically.
Key Changes Under HB 1337
Two ADUs Per Lot
Before HB 1337, most King County jurisdictions limited properties to a single ADU. The new law requires cities to allow at least two ADUs per single-family lot — in any combination of attached and detached units.
This means you could build:
- One attached ADU + one DADU
- Two DADUs (in one or two structures)
- Two attached ADUs
For homeowners, this doubles the income and flexibility potential of their property.
No Owner-Occupancy Requirement
One of the most significant changes: cities can no longer require that the property owner live on-site. Previously, many jurisdictions required the homeowner to live in either the primary home or the ADU — which meant you couldn’t rent both units or move away while keeping them rented.
Under HB 1337, you can build a DADU, rent it out, and not be required to live on the property. This makes DADUs viable investment properties, not just owner-occupied perks.
Reduced Parking Requirements
HB 1337 prohibits cities from requiring additional off-street parking for ADUs located within:
- A half-mile of a major transit stop
- A quarter-mile of a bus stop with frequent service
Even outside these zones, parking requirements have been relaxed. This is particularly impactful in Seattle and Eastside cities where lot space is limited — parking requirements previously made many DADUs impractical or impossible.
Streamlined Permitting
The law pushes cities to process ADU permits more quickly and with fewer barriers:
- Reduced impact fees for smaller ADUs
- Simplified design review requirements
- Limits on cities’ ability to impose additional conditions beyond state and building code requirements
- Encouragement of pre-approved ADU plans that can be permitted faster
Relaxed Design Standards
Previously, some cities imposed strict design compatibility requirements that effectively made DADUs prohibitively expensive. HB 1337 limits cities’ ability to impose:
- Excessive architectural compatibility standards
- Overly restrictive material or style requirements
- Design review processes that add months to the timeline
Your DADU still needs to meet building code and basic zoning standards, but the era of design review committees rejecting ADUs for aesthetic reasons is largely over.
What HB 1337 Means for King County Specifically
King County and its incorporated cities have been updating their codes to comply with HB 1337. Here’s what that looks like on the ground:
Unincorporated King County
King County already allowed ADUs before HB 1337, but the new law expanded what’s possible:
- Two ADUs per lot (previously one)
- Relaxed owner-occupancy requirements
- Clearer size and setback standards
Seattle
Seattle was ahead of the curve on ADU policy, but HB 1337 solidified protections against future restrictions and expanded allowances in zones that previously limited ADUs.
Eastside Cities
Bellevue, Kirkland, Redmond, and other Eastside cities have been updating their codes. Some cities that previously only allowed attached ADUs are now required to permit detached units as well.
South King County
Cities like Renton, Auburn, and Federal Way — which historically had more restrictive ADU policies — are now required to comply with HB 1337’s minimum standards, opening up significant new DADU opportunities.
What HB 1337 Does NOT Change
While HB 1337 removed many barriers, some rules remain:
- Building permits are still required. The law streamlines the process but doesn’t eliminate it.
- Building code compliance is still mandatory. Structural, electrical, plumbing, and energy code requirements remain in full effect.
- Size and setback limits still apply. HB 1337 doesn’t override local zoning for maximum unit size or minimum setbacks.
- Utility connections are still your responsibility. Sewer, water, and electrical connections must meet local requirements.
- Critical areas protections remain. Wetlands, steep slopes, and other environmentally sensitive areas retain their protections.
How to Take Advantage of HB 1337
If you’ve been thinking about a DADU, HB 1337 has likely made it more feasible than you realized. Here’s how to move forward:
- Check your lot: Verify that your property meets minimum size requirements for a DADU in your jurisdiction.
- Understand your local rules: While HB 1337 sets minimums, your city may have adopted even more permissive standards. Check your local code.
- Skip the parking worry: If you’re near transit, parking requirements may not apply to your DADU.
- Plan for two: If your lot and budget allow, consider building two ADUs to maximize the opportunity.
- Get expert help: A builder experienced with current regulations can navigate the updated landscape efficiently.
APEX DADU Knows the Current Rules
HB 1337 changed the game, but the rules continue to evolve as cities update their codes. APEX DADU stays current on every jurisdiction in King County — so your project is designed and permitted under the rules that apply today, not the rules from two years ago.
Contact APEX DADU to find out what HB 1337 means for your property
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