HB 1110 Middle Housing on Seattle’s Eastside: A Licensed Architect’s Guide

*By David Meade, AIA, NCARB*

If you own a single-family lot in Kirkland, Bellevue, Redmond, Sammamish, or Issaquah, the rules around what you can build on it have changed permanently. Washington House Bill 1110, signed into law in 2023, ended single-family-only zoning across most of the state. As of 2026, 84 percent of Washington jurisdictions have adopted middle housing ordinances under the law — including nearly every city on the Eastside.

What does that mean for you in practice? It means your lot that previously allowed one house may now allow two, four, or even six homes. It means a duplex, triplex, fourplex, cottage cluster, or townhouse may be a legal path forward — without any rezoning, variance, or legislative act from your city council.

I’m a licensed architect who has worked on middle housing projects across the Eastside. In this guide, I’ll walk you through what HB 1110 actually requires, how your city implements it, and what you need to know before you start designing.

What Is HB 1110?

HB 1110 is a Washington state law that requires cities to allow “middle housing” on any residential lot that previously allowed only single-family homes. Middle housing is defined in the statute as:

• Duplexes
• Triplexes
• Fourplexes
• Fiveplexes
• Sixplexes
• Townhouses
• Stacked flats
• Courtyard apartments
• Cottage housing

The key point: HB 1110 does not rezone your property. It does not change your lot’s underlying residential designation. What it does is mandate that all of the housing types listed above must be *permitted outright* — meaning a city cannot deny a permit simply because you want to build a duplex in an area formerly zoned for single-family use only.

Cities still set the development standards: setbacks, height limits, lot coverage maximums, and design guidelines. What they cannot do is say “no” to the housing type itself.

The Two-Tier System: Who Must Allow What

HB 1110 creates a tiered compliance structure based on a city’s population within its Urban Growth Area.

Tier A cities (cities with populations of 75,000 or more, plus cities between 20,000 and 75,000 within a UGA of a county with 275,000 or more population) must allow at least four units per lot in all formerly single-family zones. On lots within a quarter-mile walking distance of a major transit stop, or where at least two of the units are deed-restricted affordable, six units per lot must be permitted. These cities had a compliance deadline of July 1, 2024 — and most Eastside cities fall here.

Tier 2 cities (smaller cities under the UGA threshold — populations generally under 20,000 and in smaller urban growth areas) must allow at least two units per lot. Their compliance deadline was July 1, 2025.

The housing types that must be allowed include all nine categories listed in the statute. Cities can impose reasonable design standards, but cannot effectively prohibit middle housing types through discriminatory standards (e.g., requiring middle housing to meet setback rules that would make building impossible on standard lots).

Eastside City-by-City Breakdown

The table below summarizes HB 1110 requirements for the Eastside cities most homeowners and developers ask about.

Important note on Issaquah and Mercer Island: Both cities completed their middle housing code amendments by the June 30, 2025 deadline applicable to their planning cycle. If you’re in one of these cities, the rules are now in effect — middle housing is a permitted use on your residential lot.

What HB 1110 Means in Practice: Design Requirements

Passing a state law and building a fourplex are two very different things. Here’s what a homeowner or developer actually needs to navigate on the Eastside.

Setbacks Still Apply

HB 1110 does not eliminate setback requirements. Each city maintains front, side, and rear setbacks for residential zones. On a standard Eastside lot (typically 7,200–10,000 sq ft in many residential neighborhoods), setbacks significantly constrain the buildable area. This is where architectural design matters: maximizing unit count within the allowed building envelope requires careful site analysis.

Lot Coverage Limits

Most Eastside cities cap lot coverage (the percentage of the lot area a structure can occupy) at 40–55 percent in residential zones. When you’re designing multiple units, this cap determines whether a fourplex fits or whether you’re better served by a cottage cluster or stacked configuration. See our detailed breakdown of lot coverage, setbacks & FAR explained for how these calculations work.

Parking — A Major Relief Valve

Under HB 1110, cities cannot require off-street parking for middle housing located within one-half mile of a transit stop. On the Eastside, this is significant. Kirkland, Redmond, and parts of Bellevue and Sammamish have substantial transit coverage. Eliminating the parking requirement on a 7,500-square-foot lot can be the difference between a feasible triplex and an infeasible one — because each parking stall you don’t have to build frees up roughly 300–400 square feet of buildable area.

Building Height

Middle housing is typically capped at the same height limits as single-family homes in the underlying zone — often 30–35 feet on the Eastside. Stacked configurations (e.g., four units in a two-story fourplex) can work within these limits, but it requires a licensed architect to confirm what’s achievable on your specific lot and in your specific city’s code.

Design Standards

Some Eastside cities have adopted design standards for middle housing — requirements around roof pitch, facade articulation, window placement, and material compatibility with adjacent homes. Bellevue, for example, requires that new middle housing in established residential neighborhoods maintain visual compatibility. These standards don’t prevent construction, but they do shape design. Kirkland went further than state minimums in its 2024 ordinance, expanding the range of housing types and adopting urban design guidelines.

Urban Design Considerations: Making Middle Housing Work

Building more units on a single lot introduces design challenges that don’t exist for a single-family home. Here are the ones I deal with most frequently on Eastside projects.

Privacy between units. When you stack or attach units, windows on adjacent facades can create uncomfortable sightlines. Good middle housing design addresses this through offset windows, opaque glazing at shared boundaries, and careful landscape screening.

Sound transmission. Shared walls between attached units — duplexes, triplexes, townhouses — require careful acoustic detailing. Washington’s residential code sets minimum STC (sound transmission class) requirements, but exceeding minimums makes the units more livable and marketable. This is a design decision that needs to be made early, not at permit stage.

Separate utility access. Each unit needs its own utility connections — gas, electric, water, sewer. On a middle housing project, coordinating utility locations across multiple units, each with its own meter and service, is a significant engineering and architectural coordination task.

Visual character. One of the common concerns from neighbors about middle housing is that it will look out of place. The best-designed middle housing projects I’ve worked on take their massing cues from adjacent homes — they match eave heights, use compatible materials, and break up large building masses with articulation that reads as residential rather than institutional.

For a deeper dive into how we approach triplex and fourplex design under HB 1110, see that page.

How HB 1110 Intersects with ADUs

HB 1110 governs middle housing — it’s about adding primary dwelling units on a lot. It works alongside, not instead of, Washington’s ADU laws. A fourplex under HB 1110 and an ADU are separate uses, and the state’s ADU legislation (HB 1337, also passed in 2023) further expanded what’s allowed.

If you’re weighing whether middle housing or an ADU is the right path for your lot, those are different financial and design decisions. We’ve written about Washington ADU laws 2026 Eastside and the difference between ADU vs DADU in King County 2026 in detail if you want to compare.

Do You Need an Architect for an HB 1110 Project?

The short answer is yes — for anything beyond a simple duplex, and even then, probably yes.

Here’s why. HB 1110 establishes the legal right to build middle housing, but it doesn’t simplify the technical design work. A fourplex on a 9,000-square-foot lot in Sammamish with two ADUs and parking for four cars is a complex architectural and engineering problem. Getting the unit mix, setbacks, stair geometry, fire separation, utility routing, and facade design right requires someone with the training and licensure to stamp the drawings and take responsibility for the design.

Beyond compliance, an experienced architect adds value in feasibility analysis — telling you upfront whether your lot can actually support what you want to build before you spend money on a full set of drawings. On the Eastside, I regularly work with homeowners and small developers at the pre-design stage to establish what’s actually buildable given a lot’s dimensions, topography, tree canopy, and proximity to transit.

If cost is a concern, read our overview of how much does an architect cost in Seattle — it covers what drives fees on middle housing projects and how to budget appropriately.

Frequently Asked Questions

Does HB 1110 apply in Kirkland and Bellevue?

Yes. Both Kirkland and Bellevue are Tier A cities under HB 1110 and had a compliance deadline of July 1, 2024. Kirkland’s City Council approved middle housing code amendments on June 17, 2024, going beyond the state’s minimum requirements. Bellevue adopted Ordinances 6851 and 6852 in June 2024, allowing up to four units per lot in all formerly single-family zones, and up to six near major transit stops. Middle housing — including duplexes, triplexes, fourplexes, townhouses, cottage housing, courtyard apartments, and stacked flats — is now a permitted use in residential zones in both cities.

How many units can I build under HB 1110 on the Eastside?

It depends on your city’s tier and your lot’s proximity to transit. In Tier A cities (Bellevue, Kirkland, Redmond, Sammamish, Issaquah, Mercer Island), you can typically build up to four units per lot. If your lot is within a half-mile walking distance of a major transit stop, or if two of the units are deed-restricted affordable, you may be able to build up to six units. In Tier 2 cities (Clyde Hill, Medina), the minimum is two units per lot. Your actual unit count will also depend on your lot size, setbacks, height limits, and lot coverage maximums — which is why a feasibility review with an architect before committing to a design is essential.

Do I need an architect to build a duplex or fourplex under HB 1110?

Washington state requires stamped architectural drawings for new residential construction in most circumstances, and a licensed architect or engineer must prepare construction documents. Beyond the legal requirement, the design complexity of fitting multiple units on a typical Eastside lot — coordinating setbacks, shared walls, utility separation, parking, and fire egress — makes professional architectural services a practical necessity. An architect who specializes in middle housing on the Eastside will also help you determine what’s actually buildable on your lot before you invest in full construction documents. Contact us for a free consultation to discuss your project.

What is the difference between HB 1110 Tier A and Tier 2?

Tier A applies to larger cities — those with 75,000 or more residents, as well as cities with populations between 20,000 and 75,000 that fall within a county UGA of 275,000 or more. Tier A cities must allow a minimum of four units per lot, six near transit or with affordability conditions. Their compliance deadline was July 1, 2024. Tier 2 applies to smaller cities — those under the Tier A population thresholds — and requires a minimum of two units per lot. Their compliance deadline was July 1, 2025. On the Eastside, most cities with significant residential populations fall under Tier A, including Bellevue, Kirkland, Redmond, Sammamish, and Issaquah.

Can I build a triplex on my single-family lot in Bellevue?

Yes, in most cases. Bellevue adopted HB 1110 compliance ordinances in June 2024 that allow up to four units per lot in formerly single-family zones — and a triplex is three units, which is below that maximum. Bellevue’s ordinances specifically permit triplexes, fourplexes, townhouses, cottage housing, courtyard apartments, and stacked flats in residential zones. That said, whether a triplex is physically feasible on your specific lot depends on lot dimensions, setbacks, tree retention requirements, and slope. A pre-design consultation with an architect is the fastest way to get a reliable answer for your specific address.