Duplex connected only at the garage  

Since the new HB 1110 act addressing middle housing across different cities in Washington State was enacted last year, we have initiated several residential projects on the Eastside. While these projects are classified as duplexes under code, they are designed with only the garages connected, with all other portions of the structures remaining independent.

In this project, the two units are connected solely at the garage, while the primary living spaces are separated by approximately 10 feet. Living areas, primary bedrooms, and rooftop decks are all oriented toward the side yards, allowing each unit to feel more like a detached single-family home. Additionally, through elevation changes and horizontal offsets, direct window-to-window alignment is avoided, enhancing privacy between the two homes.

Under middle housing zoning regulations, duplex developments are allowed a higher floor area ratio, benefit from more flexible setback requirements, and exclude partial garage areas from FAR calculations, providing greater overall design flexibility. For example, if this site were developed as a single-family home, the maximum buildable area would be approximately 4,000 square feet, while a duplex development allows for up to approximately 3,000 square feet per unit (this project is approximately 2,600 square feet per unit, in addition to a two-car garage and rooftop deck, with a four-bedroom, three-bathroom layout).

We believe this “garage-connected duplex” typology will become one of the emerging trends for low- to moderate-density housing on the Eastside. On one hand, recent policy changes encourage increased housing density within traditionally low-density residential zones. In areas such as Bellevue, where DADUs were previously not permitted, most residential lots are now allowed to accommodate two to six units. Within this context, the duplex represents a balanced approach between increased density and neighborhood acceptance.

On the other hand, compared to conventional duplexes, this configuration, where units are connected only at the garage and otherwise function independently, not only improves land use efficiency but also maintains the spatial quality and privacy of detached homes. It essentially enables the development of two independent houses without the need for subdivision, and aligns more closely with the expectations of the Eastside’s low-density housing market than smaller-scale cottage housing.