Understanding the Statewide Push to Expand ADU Housing Opportunities
Washington faces a growing housing shortage, especially in cities like Seattle where developable land is limited. To address this, lawmakers passed House Bill 1337, a statewide reform that removes common barriers to building accessory dwelling units (ADUs), including detached units known as DADUs. The law empowers homeowners, real estate investors, and developers to make better use of existing residential lots.
This new legislation focuses on simplifying local permitting, increasing design flexibility, and removing restrictions that have historically slowed small-scale housing development. As a result, it creates new opportunities for families to add living space and for property owners to develop long-term rental income.
What Changed Under House Bill 1337
- Owner-occupancy requirements were eliminated. Now, property owners no longer need to live on-site to build or rent an ADU.
- Two ADUs are now allowed per lot. Property owners can build both an attached and detached ADU on the same residential lot.
- Design and permitting standards were simplified. These changes reduce review times and lower the barrier to entry for small-scale development.
Together, these changes make it easier to add housing in tight urban areas without needing to rezone or demolish existing structures. Therefore, the law aligns well with Seattle’s existing push for infill development and greater housing diversity in single-family neighborhoods.
We help clients across the Seattle area take full advantage of these updates. By working directly with the Seattle Department of Construction & Inspections (SDCI), our team ensures every project follows current code while maximizing design and placement flexibility. This guidance makes a significant difference—especially as city rules evolve to match state policy.
Key Takeaways
- House Bill 1337 removes major legal barriers to ADU and DADU construction across Washington.
- Seattle homeowners benefit directly from new state rules that support additional units and faster permitting.
- Working with a qualified contractor helps ensure compliance while taking full advantage of zoning and design opportunities.
If you’re planning a DADU project under Washington’s updated housing law, we’re here to help. Contact our team to schedule a consultation or explore your options.
Key Provisions of House Bill 1337
House Bill 1337 introduces specific changes that reshape how Washington residents can add accessory dwelling units to their properties. These provisions reduce red tape, create more design flexibility, and give homeowners greater control over how they use residential land. Understanding the core updates in this legislation is essential if you plan to build a DADU in Seattle or anywhere in Washington.
Owner-Occupancy Requirements Removed
Previously, Washington law required property owners to live on-site if they wanted to build or rent out an ADU. This restriction discouraged many potential investors and homeowners from moving forward with DADU projects. House Bill 1337 removes that requirement entirely. Now, both resident and non-resident property owners can build or rent ADUs without needing to occupy the main home. This change opens the door to more flexible ownership models and supports long-term rental strategies.
Two ADUs Now Allowed Per Lot
The new law also allows two accessory dwelling units on a single residential lot. Homeowners can now build both an attached ADU—often located in a basement or converted garage—and a detached DADU in the backyard. This provision increases the housing capacity of each property while maintaining the character of existing neighborhoods. It also supports multigenerational living and small-scale rental income on a broader scale.
Design and Permitting Standards Simplified
House Bill 1337 requires cities to ease permitting constraints and remove unnecessary delays. For example, many jurisdictions, including Seattle, have streamlined their review process for projects that follow pre-approved plans or comply with relaxed zoning standards. Design limitations around setbacks, unit size, and lot coverage have also been reduced. This makes it easier for homeowners to choose layouts that work with their lot without facing costly revisions or long delays.
Together, these three provisions form the foundation of the state’s effort to increase housing supply through small-scale residential development. By lowering the threshold to build, the law encourages more participation from homeowners and builders alike.
What This Means for Seattle Property Owners
Seattle has already taken steps in recent years to expand housing options and support infill development. House Bill 1337 strengthens that direction by aligning state law with the city’s goals. For local homeowners and developers, these updates offer new flexibility, faster approvals, and greater potential for investment.
Improved Design Flexibility for DADUs
The law gives property owners more freedom to design DADUs that meet their needs without being overly restricted by outdated building limitations. In Seattle, this means more opportunities to build larger backyard cottages or add detached units to narrow or irregular lots. Updates to the city’s zoning code—such as increased Floor Area Ratio (FAR) allowances and more generous setback rules—make it easier to design a DADU that fits both the lot and the lifestyle of the homeowner.
Expanded Opportunities for Rental Income
By allowing two ADUs per lot and removing the owner-occupancy rule, House Bill 1337 creates new pathways for rental income and long-term investment. Homeowners who previously hesitated to build now have the freedom to develop detached units for passive income. Real estate investors also gain new opportunities to add legal rental housing in high-demand neighborhoods like Queen Anne, Ballard, and Columbia City—without needing to pursue large-scale development.
Streamlined Permitting with Pre-Approved Plans
Seattle’s Department of Construction & Inspections (SDCI) has already responded to the legislative shift by expanding its use of pre-approved plans. These plans comply with local and state guidelines, allowing faster review and fewer revisions. Using a plan from our collection of pre-designed DADUs—such as the Anita or Schooner—can save weeks of back-and-forth with the city. For many homeowners, this is the fastest and most efficient path to getting started.
Overall, House Bill 1337 makes it easier to design, permit, and build DADUs that align with Seattle’s evolving zoning standards. These changes support the city’s broader effort to increase housing supply while giving property owners more control and financial flexibility.
Alignment with Seattle Zoning and Housing Goals
Seattle’s long-term housing strategy aims to increase density while preserving neighborhood character. House Bill 1337 complements that goal by making it easier to add housing units on existing lots without the need for major rezoning. In many ways, the bill reinforces the work Seattle has already done through local legislation and zoning code revisions.
Supports the Urban Residential Zoning Model
Seattle’s shift from Neighborhood Residential (NR) to Urban Residential (UR) zoning allows for greater flexibility in housing types. This includes DADUs, townhomes, and other middle housing forms. House Bill 1337 aligns with these changes by removing regulatory constraints at the state level. Together, state and local policies create a more consistent and supportive framework for small-scale residential development.
Encourages Middle Housing and Infill Development
Infill development—such as DADUs, ADUs, and duplexes—helps address Seattle’s housing shortage without relying on large multifamily projects. The new law encourages this type of growth by simplifying the process to add units on underutilized lots. For homeowners, this means they can contribute to citywide housing goals while benefiting from increased property value and potential rental income.
Enhances Seattle’s Permit Efficiency Goals
Seattle has made significant improvements to the permitting process through digital applications, consolidated plan reviews, and pre-approved floorplans. House Bill 1337 reinforces this momentum by requiring cities across the state to adopt similar streamlining practices. As a result, Seattle property owners will likely see even faster timelines and more predictable outcomes when applying for DADU permits.
By aligning state policy with Seattle’s housing vision, House Bill 1337 helps accelerate progress toward more equitable, diverse, and sustainable neighborhoods. Property owners now have more tools and flexibility to contribute meaningfully to this transformation.
Why Professional Guidance Still Matters
House Bill 1337 simplifies many aspects of DADU construction, but it doesn’t eliminate the need for expert guidance. Even with clearer rules and fewer restrictions, every property comes with its own zoning overlays, site limitations, and utility requirements. Working with a professional who understands these nuances helps ensure your project stays compliant—and on schedule.
Local Zoning Still Requires Detailed Review
While the new law overrides some local restrictions, it doesn’t eliminate all of them. Seattle still enforces detailed zoning rules related to setbacks, lot coverage, critical areas, and parking. Failing to account for these site-specific regulations can lead to delays, redesigns, and additional fees. A builder familiar with Seattle’s permitting landscape can help identify issues before they become obstacles.
Design-Build Teams Streamline the Process
At New Image Construction Management, we provide integrated design-build services that cover every phase of the project—from site review and drafting to permit approval and final construction. Our team stays current with both Seattle’s zoning code and Washington’s statewide housing laws, including recent updates related to House Bill 1337. This experience helps our clients avoid delays, reduce costs, and build with confidence.
Customized DADUs Require Expert Coordination
While pre-approved plans offer a fast path to approval, some homeowners need customized solutions to fit unique lot conditions or personal needs. We help adapt designs to meet those goals while still following city and state code. Whether you’re building a DADU in Madison Park, Green Lake, or West Seattle, our team ensures the layout works with your site—and gets approved the first time.
Legislation like House Bill 1337 creates exciting new possibilities for DADU development, but navigating those opportunities still requires local expertise. By partnering with professionals who know the system, you can take full advantage of the law without unnecessary risk.
Next Steps for Seattle Homeowners
House Bill 1337 marks a significant shift in Washington’s approach to residential development. By removing outdated restrictions and simplifying the path to approval, the state has opened new opportunities for homeowners, investors, and developers to create flexible housing on single-family lots. These changes are especially beneficial in cities like Seattle, where housing demand is high and buildable space is limited.
With the removal of owner-occupancy rules, the allowance for two ADUs per lot, and more streamlined permitting standards, property owners can now take full advantage of their land’s potential. Seattle’s updated zoning code complements this progress, offering more flexible design options and a smoother path from planning to construction.
Even with these new advantages, navigating local regulations and site-specific conditions still requires expert guidance. Our team at New Image Construction Management is here to help you move confidently through each step. From pre-permit site evaluations to full-service DADU builds, we work to ensure your project meets code and stays on schedule.
To begin planning your DADU project, browse our collection of pre-approved DADU floorplans, view our recent work, or reach out to schedule a consultation. Let’s create a smart, compliant, and lasting solution for your property.