Commercial Mass Timber Passive House Case Study

ZH set out to take the knowledge gained from their residential work which successfully combines mass timber and passive house construction into a highly sustainable product and apply it to a typical office building in an urban context.

Our analysis shows that these combined strategies result in an incredibly sustainable building with a life cycle carbon footprint 93% less than a conventional office building. These strategies are not only energy efficient, they can also help the bottom line. Lowered energy usage reduces operational costs over the life of the structure, and mass timber allows for decreased construction time and costs. Improved air quality and comfort from a passive house has also been shown to increase employee productivity and reduce absenteeism.

It is a highly appropriate time to be investigating the use of mass timber in construction because changes to model codes have been approved to allow mass timber high rise buildings up to 18 stories across the US. Currently, structural mass timber has only been approved in more forward thinking jurisdictions in limited scope with either the rewriting of local codes or through variances. These pioneering buildings have helped pave the way for the acceptance and impending wide use of mass timber in the United States.

Open Floor Plan

Applying a mass timber structural solution to a typical urban site we found that a simple system of Glulam beams and Cross Laminated Timber floor slabs can easily provide structural bays equal to or larger than a conventional cast in place concrete or steel structural system. This allows for efficient leasing spans and bays that match industry norms for office construction. 

This layout shown for a single tenant floor plan shows the adaptability for a range of typical office layouts. This plan includes perimeter offices, open office style flexible seating areas, cubicle working areas, and flexible partitioned meeting rooms.

Typical Section

Mass timber and passive house are a perfect combination because they address all of the major life cycle energy uses of a building. Operational energy use is the largest life cycle GHG (greenhouse gas) contributor in a building, and Passive House design reduces this by over 70%. The embodied energy from the materials in the building also contribute to the building’s energy and carbon footprint, and using mass timber effectively addresses this. Mass timber reduces the embodied energy of a building in two ways. First, mass timber has lower embodied energy because it requires much less energy to produce than materials like concrete or steel. Second, carbon is stored in the fibers of the wood, so it effectively sequesters CO2 for the life of the building and beyond when properly managed. Together these strategies can result in a minimum life cycle carbon footprint. In our study the mass timber Passive House reduced the life cycle GHG footprint by 77%, and if the building is designed as a Passive House Plus with renewable energy systems this increases to a 93% reduction! 

Construction Sequence

Mass timber construction has a wide range of benefits beyond its sustainability. One of the most impressive is its precision and speed of erection. Because of this precision and its panelized nature, mass timber high rises can be constructed in a fraction the amount of time required for concrete or steel buildings. In this case we determined that reduce the superstructure construction time by 66%. This not only impacts construction costs, but also can reduce interest costs on a large project. 

This building analysis also looked at the unique requirements of office occupancy. With the internal loads like equipment and servers combined with the typically large glazing ratio of office buildings, commercial office buildings tend to be more cooling dominated than residential usages, and overheating is a issue to consider. In this project we analyzed the site shading and solar radiation levels on the facade to better understand the building performance. Because this site is open on its western face, it is impacted by strong direct sun in the late afternoon that causes comfort issues from too much solar gain. To address this and provide a unique identity to the building, we designed a perforated metal screen with the scale of the perforations scaled to react to the shading on the site. 

Solar Heat Gain Study

Section Detail of Structure