11 E Lenox: Mass Timber & Passive House Multi-Family

Boston's first ground-up mass timber building.
11 E Lenox, a 7-story multifamily housing project, is the first ground-up mass timber structure in the City of Boston and Passive House Certified. The project combines the multiple benefits of mass timber and Passive House design (PHIUS+ 2018 Full Certification) to create an incredibly energy-efficient and low embodied carbon building. In a typology typically constrained by economy and a low appetite for risk, the project serves as a proof of concept for low-carbon market-rate housing, the result of synthesizing novel technologies and systems through a committed and rigorous integrated development & design approach.

The mass timber is sustainably & regionally sourced and is a carbon sink while also being a less carbon-intensive material to produce than concrete or steel alternatives. Working in tandem with mass timber's excellent thermal insulating properties, the building is Passive House designed and Certified with a robust thermal envelope and novel active building systems designed to be 81% more efficient than a conventional baseline equivalent.

The project’s combination of embodied and operational carbon reduction design mutually serves both stakeholders and end-users, providing a robust, comfortable, and healthy living environment for its occupants while drastically reducing operating costs for both user and operator. The embodied and operational savings reduce the building’s overall carbon impact, benefitting the local community and beyond.

The project precedes the BPDA/BSA Mass Timber Accelerator Pilot program and the City of Boston’s upcoming Passive House requirement for multifamily buildings, providing a built reference for the next wave of Boston housing. The project serves as precedent and as an advocacy tool by the City of Boston’s Planning Department, presented as a Boston Resilient Building Case Study to illustrate emerging and exemplary mitigation and climate change adaptation.

Additional Info:
Phius Full Certification: Phius Database Link
Recipient of a Boston Society of Architects 2023 Design Award: BSA Link
WoodWorks - Wood in Architecture 2024 Design Award: WoodWorks Link
mass timber installation

Location

Boston, MA

Type

Mass Timber, Multi-Family Residential

Status

Completed 2022

Details

  •     • 43,000 sq. ft
  •     • 7 stories under 70ft
  •     • 34 market rate rental units
  •     • Passive House PHIUS + 2018 Design Certified

Team:

  • • Haycon
  • • BLW Engineers
  • • H+O Structrural Engineering
  • • Passive to Positive
  • • Code Red Consultants
  • • Charlotte Nakhoul

Photography:

  • • Jane Messinger

Awards:

  • • BSA - Design Award Recipient, 2023
  • • WoodWorks - Wood in Architecture, 2024
A Boston first: Mass Timber Proof-Of-Concept
As the first ground-up mass timber building in Boston, its realization from concept to built structure was the culmination of proactive and collaborative efforts from the entire development team. Through precedent study, research, and visiting mass timber projects in the northeast region; the team connected with industry experts and liaisons to guide our initial fact-finding efforts through a rigorous feasibility phase, eventually leading to the final mass timber design that is implemented in the diagram below. 

A Practical Hybrid Approach

While the majority of the structure is mass timber, a hybrid approach was utilized to meet the specific conditions of this project. A parking garage at grade, with its vehicular design and clearance restrictions, necessitated the use of 7 steel posts for structural transfer and clearance height, for which a mass timber solution would have pushed the building over the high-rise threshold and its more onerous code requirements.
A New Archetype for Boston Housing
As a mass timber Passive House building, the project serves as a proof of concept and a model for the next generation of housing under Boston’s low-carbon building initiative. As the first ground-up mass timber project in the City of Boston, it precedes both the City’s Mass Timber Accelerator pilot program and the current Passive House requirement for multifamily buildings over 12,000sf.

From a developer’s viewpoint, mass timber design presented a unique opportunity to deliver vertical density in an urban infill site – the highly efficient mass timber structure affords vertical efficiency and increased density in enabling 7 stories under 70 feet to roof, a critical high-rise height threshold exclusive to Massachusetts building code that usually sets a soft cap of 6 story construction for midrise housing using conventional construction (steel, concrete). The mass timber design allows an additional story over conventional construction while staying below the high-rise threshold and its associated costly building code and life safety requirements.

In our research and feasibility phase, we realized the potential embodied carbon benefits of the mass timber structure and pursued a path to incorporate low operational carbon Passive House design. The development team recognized the overall impact that a mass timber Passive House housing project could have, benefitting development stakeholders with market differentiation while also providing occupants with comfortable, healthy, energy-efficient housing and the overall community with a synthesized proof of concept for the City of Boston’s goals of overall carbon reduction.

It is net zero ready with its all-electric design, equipped for the switch to a clean power grid, and uses high-performance but relatively conventional systems for ease of future maintenance and replacement. The mass timber structure ensures a long building life, with a robust envelope design providing a durable shell to complement its strong bones.

The project’s biggest impact may be that it can serve as a model for sustainable housing development in Boston – the result of a committed and rigorous integrated development and design process, synthesizing a team-wide sustainability ethos with a pragmatic, cost-conscious approach. 11 E Lenox is used as an advocacy tool by the City of Boston’s Planning Department, presented as a Boston Resilient Building Case Study to illustrate emerging and exemplary mitigation and climate change adaptation.

Additional Info:
Boston Planning Department Case Study: Case Study Link
Boston Climate Resiliency Case Study: Case Study Link
A winning combo: Mass Timber + Passive House Sustainable Design
Passive House design seeks to lower the overall consumption of operational energy with a combination of passive and active systems, while also encouraging the use of eco-friendly materials and products that are less carbon-intensive to produce. Mass timber is the ideal structural system choice in reducing a building's overall embodied carbon, and with its excellent thermal properties it also contributes in creating a robust passive building envelope that reduces thermal bridging and heat loss.
A vast reduction: Embodied Carbon & Operational Carbon
The building utilizes several strategies and systems that work to decrease its overall carbon impact, holistically designed to lower both its embodied carbon footprint and its operational consumption.

12.8 kBTU/sf pEUI

81% energy reduction

The passive house building projects to use 81% less energy than a baseline building EUI of 65, according to the 2030 Challenge baseline metric

844 tons of CO2 stored

327 tons of CO2 offset

The mass timber superstructure stores 844 metric tons of CO2 during its building lifecycle, while saveing 327 tons over conventional steel or concrete alternatives
2030 Challenge score, created with ZeroTool
PHIUS+ 2018 building metrics
Holistic & Integrated Design: Enabling Density Feasibility with System Efficiency
Utilizing a novel structural system for its vertical space utilization benefits requires proactive coordination and management of systems integration. MFDS led the design team in vetting and coordinating the various systems approaches to maximize space utilization and mitigate unknown factors and potential pitfalls/pain points, designing efficient vertical stacks and ensuring that horizontal MEP systems ran high and tight within the structural plenum.

For this particular project, MFDS realized that a double glulam beam system provided both structural and MEP systems benefits. In addition to its architectural flexibility, the double beam system provides a 6” clear gap at gridlines, allowing for vertical MEP stacks to run in walls located along the gridlines. In more conventional steel and concrete construction, MEP verticals are typically avoided along these structural gridlines.