Washington Duplex Builders
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A New Era for Duplexes in Washington: Understanding HB 1110
At HiLine Homes, we keep homeowners and real estate investors informed on housing laws that can help unlock the full potential of their lot. One such law, Washington State’s newly enacted HB 1110, creates exciting opportunities to expand living space or grow their rental portfolio through increased housing flexibility.
HB 1110 is Washington State’s “middle housing” law that was passed to address the housing shortage and affordability crisis. This law overrides local zoning restrictions that previously limited many neighborhoods to single-family homes only. Now, in most urban and suburban areas, you can build a duplex in Washington.
What Does HB 1110 Allow You to Build?
Cities in Washington must now allow more multi-family homes in neighborhoods previously restricted to detached houses. Under HB 1110, tiered permissions are based on city population and transit proximity:
- Small cities (under 25k): typically 2–4 units
- Medium cities (25k–75k): up to 4 units
- Larger cities and areas near transit: up to 6 units
This change unlocks real opportunities for homeowners to add value, create income-generating properties, or design homes for multi-generational families.
Why This Matters to Homeowners
HB 1110 creates a pathway for homeowners towards more affordable housing through efficient land use. The following property owners now have new rights and opportunities to develop duplexes and other middle housing types without rezoning:
- First-time homebuyers wanting to offset their mortgage with a rental unit
- Investors and families looking to build equity through custom stick-built duplexes
- Generational households or those planning for long-term care
Many homeowners may feel overwhelmed by the legal details that HB 1110 entails. Here is where HiLine Homes comes in. We simplify the process and help you navigate and apply the benefits HB 1110 provides to your unique lot. Below is what the law allows for homeowners in each city and region.
Washington "Middle Housing" Density Guide (HB 1110)
If Your City’s Population Is… | In All Residential Zones, You Can Build… | Within 1/4 Mile of Major Transit, You Can Build… |
|---|---|---|
Over 75,000 (e.g., Seattle, Spokane, Tacoma, Vancouver, Bellevue) | At least 4 units (e.g., a fourplex) | At least 6 units (e.g., a sixplex) |
25,000 – 75,000 (e.g., Olympia, Walla Walla, Lynnwood, Woodinville) | At least 2 units (e.g., a duplex) | At least 4 units |
< 25,000 (in a large county's UGA) (e.g., Ellensburg, Sumner, Grandview) | At least 2 units (e.g., a duplex) | (Same as base zoning) |
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Why Build a Duplex in Washington?
Now that you know how many units you can build in your lot, here are the many advantages your lot can provide you when you build a duplex or more:
Strong Rental Income Potential
Duplexes offer steady, long-term rental income, especially in high-demand cities like Seattle, Tacoma, and Vancouver. With rental demand outpacing supply in many Washington housing markets, duplex owners can command competitive rates and experience low vacancy.
House Hacking for Mortgage Relief
House hacking is a popular strategy for savvy homeowners where you live in one unit and rent the other. Rental income from the second unit can cover part or all of the mortgage, significantly reducing monthly expenses. Duplexes are also a solution for multigenerational families with adult children or aging parents.
Cost Efficiency of Duplex Construction
Building a duplex in Washington is far more cost-effective than constructing two individual single-family homes, only costing approximately 63% of the total. Since duplexes share components like the foundation, central wall, plumbing, and roof, this reduces both material and labor costs.
Zoning and Permitting Support for Your Duplex Project
Many buyers are uncertain about what they can build after HB 1110, with first-time homeowners and investors being overwhelmed by zoning and permitting alone, as every jurisdiction has its own unique regulations.
With our preconstruction expertise on Washington’s zoning and permitting process, we can help you navigate your permitting requirements, whether it’s in Everett, Puyallup, or any of the communities we serve across the state. Through our guidance, you can move from duplex design to construction faster, more confidently, and in compliance.
Plan 3322: A Smart, Profitable Layout
Plan 3322 is a flagship option in HiLine’s duplex series, designed to serve owner-occupants and rental investors alike. Each unit has features that make it easier for residents to enjoy independent lifestyles while living side-by-side.
- 3 bedrooms and 2.5 bathrooms
- A private single-car garage
- An open-concept dining and living area
- Walk-in closets in each primary suite for ample storage
The mirrored layout ensures equality in amenities, appealing to both renters and homeowners with separate entrances and private outdoor spaces.
The Cost to Build a Duplex in Washington State
At HiLine Homes, our streamlined construction process and bulk material purchasing help reduce costs without sacrificing quality. As an experienced duplex builder in Washington, we offer transparent pricing and a full breakdown of cost estimates during our consultation.
Factors that impact duplex construction costs include the following:
- Land acquisition: prices vary drastically by region and zoning potential
- Permits and fees: e.g., Everett’s permitting schedule includes impact fees, utility connections, and more
- Site prep and foundation work
- Framing and roofing
- Interior finishes, including flooring, cabinets, and fixtures
- Exterior finishes such as concrete, paint, and landscaping
Start Your Duplex Project With Us
At HiLine Homes, we help you build an affordable duplex to unlock the potential of your lot, provided by the newly enacted HB 1110. With a duplex on your lot, you can obtain homeownership, the ability to house a loved one close to you, and long-term investment.
Ready to build a duplex on your lot through a proven, streamlined process? Consult with a Home Consultant today near you.