The Sustainability Case for Cross Laminated Timber

James Woods, mechanical engineer with Tetra Tech’s High Performance Buildings Group, discusses how timber is a change agent in sustainable design within the built environment.

The timber trend is beginning to gain traction as a potential change agent in sustainable design within the built environment—particularly in forest-heavy areas of the United States, such as the Pacific Northwest. The trend is due in large part to the increasing availability of cross laminated timber (CLT). CLT is a prefabricated material consisting of sustainably-sourced lumber layered in opposing directions and held together with low volatile organic compound (low-VOC) adhesives. The result is a powerful load-bearing material that is proving its mettle as a competitor to steel and concrete.

The timber trend is causing many building design professionals to come around to the idea that wood structures are a sustainable approach. But what are the environmental benefits? According to The Architect’s Newspaper, using timber as a structural material reduces the associated carbon emissions of a building in three ways:

  • Renewability: Wood is a renewable resource with a lower extraction and processing impact than steel and concrete
  • Abundancy: Because trees are a profoundly available domestic resource, the embodied carbon in timber is significantly lower than that of steel or concrete— especially when steel and concrete require importing materials from other parts of the world
  • Increased sequestration: The more wood we harvest, the more we can replant, increasing the land’s carbon sequestration capacity

This final point may seem a little counter-intuitive, but substantial research is being done on the subject of a monitored increase in timber harvesting. It begins to make more sense when we learn that much of the wood harvested to make CLT are the trees that are decaying due to the infestation of mountain pine beetles—releasing more carbon into the air, rather than absorbing it.

Coupled with the emerging trend of mass timber structures is the interior design concept of exposing all building services such as ductwork, chilled sails, fire protection piping, and more. This idea has branched out of the tech office space into a mainstream approach of designing a more industrial and functional indoor experience. By removing dropped ceilings, interiors feel more spacious. Additionally, exposing wood structures creates an aesthetically pleasing and natural environment, as opposed to the more traditional concrete or steel.

Healthy Building Design

There are several ways these trends promote sustainability in modern work spaces. We are continuing to investigate and learn about the benefits of different design approaches that value the health and well-being of the occupant. Pulling from the knowledge found in the WELL Building Standard, there are three relevant concepts that can contribute to the overall performance of a building:

  • Beauty and design
  • Biophilia
  • Material transparency

According to the WELL Standard, “integrating aesthetically pleasing elements into a space can help building occupants derive a measure of comfort or joy from their surroundings.” Presenteeism—the idea that while staff are present, they are often disengaged from work—is a major issue in office spaces. Thoughtful design and the use of natural materials can help mitigate this.

Biophilia addresses our affinity to the natural world, and through incorporating environmental elements and natural patterns, interior spaces can “help to speed up healing and recovery time, boost positive feelings, and reduce negative ones,” according to the Well Standard. This is of particular use in healthcare facilities, where biophilic design has demonstrated improved speed of patient recovery, leading to more availability for new patient intake, and office environments, where it has shown a reduction in lost time from staff fatigue.

People should have transparency in the materials used for the construction of the building they occupy, including the myriad of chemicals that are constituents of seemingly harmless components. With wood, the only component we need to be aware of are the adhesives used to create cross laminated timber and glulam products. There are environmentally sound products for this application.

Sustainable sourcing combined with thoughtful interior design can lead to gains in productivity and energy efficiency. We are continuing to investigate the benefits of timber design and are already integrating it into commercial projects. As we move closer to a future of net-zero and net-positive design, the inclusion and demand of natural material will prove critical.

James Woods, PE, WELL AP, Mechanical Engineer

Image courtesy of the Oregon Department of Forestry