By Holly Lennihan, RA, LEED AP and Thomas Corrado, LEED AP
It’s no secret that buildings are a major contributor to carbon dioxide emissions. For years now, architects, engineers, and the design community as a whole have taken measures to reduce the industry’s impact on climate change, fervently pursuing innovative solutions that could help remedy – if not reverse – the damage. Enter: the resurgence of wood construction, now in the form of mass timber.
Mass timber is a readily renewable construction material that sequesters carbon from the atmosphere for the lifetime of its usage. Its sustainable qualities combined with its aesthetic appeal and structural capabilities have captured the attention of American architects such that over 220 projects in the country currently feature mass timber – and the number of opportunities is expected to rise. Heightened awareness of climate issues, government mandates, and a consumer demand for environmentally conscious options have driven an increased exploration of materials like mass timber that will not only address sustainability concerns, but help aesthetically differentiate properties as well.
At Hickok Cole, we’ve spent the past three years working internally and alongside industry partners, including Arup, DPR Construction, and Davis Construction, to learn as much as we can about the opportunities, challenges, and capabilities of building with mass timber. To help prepare for the inevitable mainstreaming of mass timber, we’ve pulled together a primer to share a few things you should know:
Currently, much of mass timber is manufactured in Europe, Canada, or the West Coast which can translate to longer lead times for projects in the United States, specifically those on the East Coast. Fortunately, these lead times can be offset by the speed of mass timber construction. Unlike with concrete or steel, mass timber can be assembled with a much smaller team in much less time – sometimes within the course of a few weeks.
Another challenge that comes with importing mass timber is the subsequent increase in cost, making the decision to use mass timber over its more competitively priced counterparts a difficult one. Positioning mass timber as a differentiator within a competitive marketplace has been a successful strategy for increasing its use. In Washington, D.C., for example, the material is perceived by buyers as a unique aesthetic advantage, allowing for owners to offset the material cost by charging a premium on rent.
Addressing Codes & Safety Precautions
Stick built systems fell out of fashion following the industrial era when fires ravaged much of Chicago and San Francisco. Even with the technological advances of today, a cautionary approach remains surrounding the construction of large, commercial buildings out of wood. As with many forms of technology in their infancy, there is a limited amount of tested product available from which to base findings from, identify challenges, or point to solutions. In order to address these kinds of barriers to entry, it’s crucial to get to know the local officials and open a dialogue well in advance around the regulations and restrictions that surround mass timber construction.
In addition to local officials, there are several resources available online that have proved helpful for our design teams. From advocacy groups like Wood Works and the American Wood Council to mass timber suppliers themselves, these organizations provide helpful guidelines for getting started.
Connecting with like-minded firms within the industry can also prove very helpful for sourcing supplemental information. Consider reaching out to past partners or clients to ensure that all aspects of design and construction have been thoughtfully considered. Assembling a strategic team that includes engineers, builders, and designers is not only efficient but cost effective. It allows each team member to investigate their own area of expertise, strengthening the group’s collective knowledge and creating a web of mass timber advocates within the industry.
Finally, and of utmost importance, is the sustainability component of this story. In cities like Washington, D.C., buildings can contribute over 70 percent of the greenhouse gas emissions produced. Identifying innovative solutions to decrease the built environment’s carbon footprint is of paramount importance and it is crucial that the design community leverage their knowledge of mass timber to propel the movement forward.
Case Study: CLT Goes to Washington
Washington, DC-based architecture firm, Hickok Cole anticipated the mass timber trend and sought to mainstream the material within the local marketplace. Focusing on Cross Laminated Timber (CLT) – a type of mass timber consisting of several boards stacked and glued together in alternating directions – the team partnered with Arup and DPR Construction to conduct an extensive study of the material, reviewing case studies and reaching out to local code officials to start a dialogue about the material’s use in DC. After a thorough analysis of cost and the coordination between the structure and building system’s infrastructure that proved feasibility for commercial development, the team set out to put their knowledge to the test.
Columbia Property Trust felt it could create incremental value for its investors by adding floors to 80 M Street SE, an existing DC office building with unused floor area ratio (FAR) square footage. In partnership with Davis Construction and Arup, Hickok Cole pitched a three-story CLT addition reasoning that the incremental increase in construction costs could be offset by a higher per-square-foot lease rate. The concept design – which features an all wood interior visible from the street through a glass curtain wall – differentiated the space so effectively within the competitive DC market that a tenant expressed interest before design development even began.
The Contextual Challenges
In Washington, DC, adding floors to an existing building is common, especially when the zoning regulations translate to underutilized leasable area. One of the key issues is the capacity of the existing building to accommodate the additional weight. In the case of 80 M Street, one of the advantages of the CLT structure was its light weight which minimized existing column reinforcement and resulted in no foundation reinforcement.
Another consideration was the code regulation which allows for mass timber structures to reach 85’-0” feet in height. The 2021 code will allow mass timber structures to reach 270’-0” feet, but will require additional fire protection measures to reach these heights, which has prompted some code officials to accommodate CLT through code modifications. In the case of 80 M Street, the design team sought to build wood over 85’-0” in height as the proposed addition would add a 3 story Type IV wood structure on top a seven story Type 1A concrete building. One of the aesthetic goals for these floors was to showcase the wood by leaving it exposed which was made possible by the building having access to all four sides for fighting access and additional fire safety measures including increased fire resistance ratings, an improved fire water supply, addition of a redundant fire pump and an upgraded sprinkler system, to mitigate most of the concerns regarding fire suppression.
The 3 additional stories of CLT structure are comprised of CLT slabs supported on Glulam columns and beams. The column grid in the addition matches the existing column grid of 30’-0”x30’-0” below. Because timber is lightweight, larger grids can result in vibration performance issues. To improve the floor vibration performance of the timber structure, stiffer, deeper beams were used, which were accommodated by additional floor height. This design challenge led to taller floor to floor heights that provide unparalleled open space in the DC market. The additional height also allowed the design team to wrap the building in floor to ceiling glazing, enhancing its biophilic nature and provide increased access to natural light for its prospective tenants.
Construction of the mass timber vertical expansion at 80 M Street is expected began in 2020.
Holly Lennihan, RA, LEED AP is a Director of Sustainable Design and Senior Associate at Hickok Cole with over two decades of industry experience working on a variety of project types including, historic preservation and adaptive reuse, corporate interiors, multifamily housing, and master planning studies. Currently, Holly spearheads Hickok Cole’s High Performance Building practice and is the project manager for the American Geophysical Union’s headquarters renovation to net zero energy. Under Holly’s leadership, Hickok Cole has won a series of state and federal grants focused on sustainability, resilience and urban ecological systems. Her team was awarded a United States Forest Service Wood Innovation Grant to design the Kingman Island Ranger Station out of cross laminated timber, resulting in a more comprehensive understanding of how to incorporate mass timber into the firm’s holistic design offerings.
Thomas Corrado, LEED AP is a Senior Associate and architect at Hickok Cole, where he works for the firm’s Commercial Architecture practice. His expertise in urban studies, place making, digital fabrication, and sustainable design has been applied to projects ranging from large scale commercial interiors to build to suit. Of late, Tom has been an integral member of the design team for 80 M Street, Washington, DC’s first mass timber commercial office renovation. His noteworthy projects include the Center for Strategic and International Studies headquarters and Anthem Row.