154 Broadway

154 Broadway shows how hybrid wood construction can meet the stringent energy efficiency requirements of Passive House certification for multi-family housing. The five-story building blends affordable light-frame wood walls with efficient mass timber floor and roof panels, leaving the panels exposed to create an aesthetic that differentiates this development from others in the region. The net zero-ready project, with all-electric mechanical systems, gave the developer a zoning density bonus because it reduced demand on the electrical grid while increasing the City’s housing supply. 
 
The 38,250-square-foot structure—four stories of wood-frame residential units over a composite steel podium with commercial and retail space—contains 40 studios plus five one- and three-bedroom apartments. Nine units are reserved for income-restricted residents. 
 
To meet rigorous Phius CORE 2021 Design Certification requirements, the project team took advantage of prefabrication to ensure an airtight fit between the cross-laminated timber (CLT) panels and other structural wood members. They wrapped continuous exterior insulation around the building envelope for increased thermal comfort and energy efficiency and maximized the value of the airtight envelope by adding high-performance windows, efficient heat pumps, and strategically placed sunshades. An added benefit is that the thermal mass of the CLT and gypcrete topping slab mitigate indoor temperature fluctuations and enhance comfort while reducing utility costs for residents. 
 
The hybrid structure combines bearing and non-bearing light-frame wood stud walls with CLT floor and ceiling panels, which are left exposed in units and common areas to highlight the natural beauty of wood. Steel columns and beams provide structural capacity where needed, although CLT easily spanned most studio units without need for additional beams or columns, allowing residents to utilize every square foot of their space. 
 
The tight envelope and increased heating and cooling efficiency helped reduce duct sizes. This supported the decision to expose CLT in unit living areas, since the smaller ducts could be more easily concealed. To minimize visual clutter, the team mounted light fixtures on the walls, avoiding the need for electrical conduit on ceilings.  
 
As part of a pilot project promoting CLT made from trees native to the northeastern U.S., the team incorporated panels made from eastern hemlock and tamarack for exposed applications in select common areas. This allows interested building professionals and academics to view the panels in situ while minimizing disruption for tenants. 
 
The design team worked closely with building officials to show how the natural fire resistance of CLT could be combined with load-bearing light-frame wood walls to meet Type V-A requirements. To manage acoustics, they upgraded their assembly with a mat specifically designed for use with CLT. The mat was topped with gypcrete and a special flooring product which helped further reduce noise. 
 
154 Broadway’s structure and envelope assemblies are highly replicable, using readily available wood materials in ways that are both cost effective and energy efficient.