By Luke Carothers
It is no surprise that there is a massive push in the AEC industry to build more sustainable projects. To facilitate this push towards sustainability, engineers and researchers are turning to new, alternative materials. One of the most promising amongst these new materials has been in the engineers’ repertoire for thousands of years: wood. Today’s engineers are not using our ancestor’s wood, however; they are using mass timber products.
Mass timber products are created when layers of wood are glued, nailed, or doweled together. This process results in strong and versatile structural panels, beams, and posts. In addition to strength and versatility, mass timber products carry a significantly lower carbon footprint compared to building materials such as steel and concrete.
One firm leading the way in mass timber projects is Arup who is currently serving as Project Engineer for Washington DC’s first mass timber overbuild project: 80 M Street SE. This commercial office building is the first in Washington DC to feature additional floors entirely constructed using mass timber. Additionally, 80 M Street SE is currently on pace to be the first high rise overbuild timber structure in North America.
The property is owned by Columbia Property Trust; who were looking to add rentable square footage to maximize the allowable height limit for the site without having to reinforce the existing structure or foundations. Working with the project architect Hickok Cole, Arup proposed using mass timber to reduce the weight on the existing structure. Not only would using mass timber achieve the goals of reduced weight and sustainability, it would also create a distinctive facade.
There are several advantages to using mass timber, from both a sustainability and building perspective. As a renewable resource, mass timber products inherently carry a significantly lower carbon footprint compared to steel and concrete. According to Matt Larson, Arup’s Buildings Practice Leader and Associate Principal in Washington DC, many developers “shy away” from using mass timber on their projects due to cost, building code restrictions, and lack of policy incentives. However, Larson believes that mass timber’s sustainable, low carbon benefits can outweigh these issues.
One of the biggest challenges for firms looking to build using mass timber in North America is contending with current building codes. In most of the United States, the adopted version of the International Building Code (IBC) limits the height of timber buildings to 85 feet. The team at Arup was prepared to overcome these challenges. Larson believes they were well equipped to handle coding modifications based on previous joint-research completed with the project’s architect, Hickok Cole. According to Larson, this research, “[allowed] the teams to align closely on the project’s vision and serve as the basis for the design concept proposed to Columbia Property Trust.”
After Columbia Property Trust accepted the design concept, the project then had to be submitted to Washington D.C. Code Authority for approval and vetting. To prepare for and maneuver through this process, the team at Arup leveraged its extensive knowledge of code consulting and timber structures, working closely with the Department of Consumer and Regulatory Affairs to receive a code modification for the use of mass timber on a high rise building. The code modifications required for the project required taking a multidisciplinary approach. After early meetings with the chief building official, the code consulting team determined that this multidisciplinary approach must demonstrate that redundant systems would be put in place to achieve a high level of life safety. Additionally, these modifications were site specific and included fire department access on all four sides as well as a secondary fire pump.
Also included in this multidisciplinary approach was a critical focus on the structure’s connections. With a lack of mass timber projects in the works, there is currently a lack of fire-tested connections on the market. To solve this problem, Larson says Arup turned to their structural and fire engineers who developed new concepts for the project’s two-hour rated exposed timber connections. These concepts were then further designed and tested by Katerra, the project’s timber design-assist partner and supplier/erector, alongside Arup’s team. This testing partnership ensured that the connections and redundant systems would work, demonstrating the design’s viability and safety to the code authority.
Teams were further able to save capital as a result of mass timber’s light weight. During a typical vertical building expansion, existing foundations usually need to be strengthened to support the weight of the new section. This result is usually some form of building closure. However, 80 M’s mass timber design means that no changes need to be made to the foundations or support columns. The added benefit of this lack of change is that the building does not have to shut down while renovations are made.
When finished, 80 M will not only be unique in terms of material, but also in terms of its holistic design. 80 M’s design is biophilic-inspired, taking occupant health and wellness into consideration by maximizing their connection to nature. The project, which provides an additional 100,000 square feet to the building in the form of two additional floors, also features a rooftop terrace.
This project is indicative of a movement towards newer, sustainable building materials. As more projects of this nature as undertaken, approved, and completed, the feasibility and benefits of building in mass timber become more clear. 80 M will not only be a beautiful addition to the Navy Yard neighborhood, but also a symbol of our progress towards sustainability.
Luke Carothers is the Editor for Civil + Structural Engineer Media. If you want us to cover your project or want to feature your own article, he can be reached at firstname.lastname@example.org.