Seattle Middle Housing: A Technical Guide to the Adopted HB 1110 Middle Housing Code Changes
May 20, 2026
Key updates and opportunities Seattle Multi-Family Residential Developers need to know.
Seattle’s response to Washington State House Bill 1110 has now moved from interim compliance to adopted code. Through the One Seattle Plan and permanent legislation approved under Ordinance Nos. 127375 and 127376 late last year, the City has established a new Middle Housing framework intended to expand residential capacity in zones that historically allowed predominantly detached homes.
For Seattle and Pacific Northwest multi-family residential developers, the significance of these changes is not simply regulatory; the practical implications are architectural, financial, and site-specific. Revised standards for density, FAR, lot coverage, setbacks, height, amenity area, parking, stacked units, ADUs, low-income housing, and limited ground-floor commercial uses all influence what can be designed, entitled, financed, and built on a given parcel.
To help developers and project teams understand these changes, AXIS Architecture + Design has prepared a concise technical summary of Seattle’s updated Middle Housing standards. The summary includes code highlights and yield studies illustrating how the new framework may affect typical Neighborhood Residential lots, including detached, attached, semi-detached, and stacked-unit configurations.
As Seattle’s housing policy continues to evolve, early technical analysis will be essential to identifying development opportunities and minimizing planning risk. As an experienced Seattle-based multi-family residential architectural design firm, AXIS’ summary is intended as a practical starting point for owners, developers, and project teams evaluating sites under the City’s adopted HB 1110 implementation framework.
Download AXIS Architecture + Design’s Seattle Middle Housing white paper below.
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Have a multi-family residential project proposed in Seattle, Washington State, or along the West Coast? Connect with AXIS Architecture + Design’s Multi-Family Residential design practice to see how we can help. As an award-winning architecture firm with extensive experience designing multi-family residential housing, workforce housing, affordable housing, and mixed-use projects across the Pacific Northwest and along the West Coast, AXIS Architecture + Design has the planning, design, and feasibility expertise to help ensure your project’s success.