Reaching New Heights in Sustainable Design: Winthrop Center

Winthrop Center, located in Boston’s financial district, is a striking 691-foot mixed-use tower comprising 812,000 square feet of office space and 321 luxury condominiums. Completed in 2022, the tower became the largest Passive House Institute–certified office building in the world.

Designed by Handel Architects for Millennium Partners Boston, Winthrop Center was envisioned to set a new standard in energy-efficient skyscraper design. Passive House certification recognizes buildings that achieve exceptional performance through airtight construction, insulation, and advanced ventilation systems. The office portion of Winthrop Center is expected to use significantly less energy and deliver more fresh air compared to similarly sized projects in the region.

The project has been recognized with multiple honors, including LEED Platinum as well as targeting WELL Gold, underscoring its innovative contribution to sustainable architecture.

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A Complete Silicone System

To support its ambitious design goals, the project required a high-performance facade system that could deliver strength, durability, and long-term weatherproofing. The fabricator, Harmon (formerly Sotawall), selected a full suite of silicone sealants and weatherproofing solutions.

• ‍UltraGlaze™ SSG4650 structural silicone glazing sealant – Provided 30 psi design strength. This strength enabled slimmer mullions, wider sight lines, aluminum savings, and higher facade performance. (UltraGlaze SSG4600 sealant is also available with the same capability.)
• ‍SilPruf™ SCS9000 NB sealant, SilPruf SCS2000 sealant, and SCS2350 sealant – Delivered flexible, long-lasting weatherseal performance across the facade.
• ‍UltraSpan™ UST Weatherstrip – Added further durability and weatherproofing, contributing to the complete system.

Together, these products help to create a robust, flexible, and weather-resistant facade designed to perform for decades in Boston’s challenging climate.

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Cutting-Edge Silicone Sealants

These high-performance silicones help enable more sustainable, high-performing projects like Winthrop Center by combining structural stability, weather resistance, and long-term durability. They are designed to expand architectural possibilities while helping maintain building performance and integrity over time.

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Project Partners

• ‍Developer: Millennium Partners Boston
• ‍Architect: Handel Architects
• ‍Collaborating Architect: DREAM Collaborative
• ‍Facade Fabricator: Harmon (formerly Sotawall)
• ‍Construction Manager: Suffolk Construction

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Note: Performance results are those of reported accounts, and are not to be relied upon as typical or expected under any other circumstances. Performance results will vary depending upon a number of factors. Prospective customers should rely solely upon their own evaluative techniques to determine what results are attainable and optimal to their specific needs. Further note that MPM is not endorsed by or affiliated with the owner(s) of Winthrop Center.