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May 5, 2023


Photo by Moris Moreno
Onni South Lake Union encompasses two 42-story residential towers and a 13-story midrise, making it the largest residential project in Seattle’s history.

Onni South Lake Union

Location: Seattle

Contractor: KHS&S Contractors

Architect: Chris Dikeakos

Team: Laborers International Union of North America; Northwest Carpenters Union; CWallA; Foundation Building Materials; GTS Interior Supply; L&W Supply; Spears Construction Supply; Hilti; Plexxis Software; Steeler

Onni South Lake Union encompasses two 42-story residential towers and a 13-story midrise, making it the largest residential project in Seattle’s history. As the Canadian Onni Group’s first project in Washington, the developer turned to KHS&S for its expertise in interior metal framing, drywall and finishing.

The KHS&S team constantly analyzed building design, systems, equipment and materials to meet the required performance levels, quality and safety while remaining within budget. KHS&S tested and selected a more efficient ceiling system, moving away from the original spec drawings.

After reviewing multiple options, a short span ceiling system was chosen as the pre-engineered solution fell within the width of each unit and eliminated a support brace. This system was quicker to install, had fewer components and was much stronger.

With 632 miles of steel framing, the QML automated laser layout system was used. When framing CAD drawings are plugged into the software, two laser beams make a visible “X” at the correct point on the floor and ceiling, eliminating any miscalculations and increasing speed through automation.

Prefabrication and repetition efficiencies were achieved by the use of the PanelMax machine to prefabricate drywall assemblies off site, which greatly contributed to project success by increasing productivity. The machine also cut more than 5 miles of plywood rips and 15 miles of gypsum shapes. Each of the 1,179 residences required multiple three-dimensional corner pieces, which the machine could repeatedly produce. An on-site panel saw was continuously operated to cut plywood to the exact width of units. As efficiencies with the PanelMax machine and panel saw were perfected, a one- or two-second improvement saved substantial time over four years. Precut studs to specified size were then ready to install, reducing the need to cut thousands of studs for each floor.

Connecting with the community, KHS&S engaged local talent for office and project personnel. While attending a career fair with the University of Washington, KHS&S met with students completing their construction management degree and seeking employment after college. Long-term relationships with trades in the Seattle market ensured an additional workforce was available from local labor.

A project of this scale, spanning more than four years, by its nature, is challenging. The KHS&S craft workers pushed the limits of innovation by managing multiple design challenges and changes. Despite the enormous difficulties of managing a project of this scale, amidst the pandemic’s relentless obstacles, the quality of the finished product illustrates how KHS&S demonstrated excellence in all work scopes.

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