Work has been completed on the 80 M office building in Washington DC. The project, which saw a three-story timber extension added atop an existing seven-story concrete building, is described by the design team as “the first commercial office building in Washington DC to feature a vertical extension constructed using mass timber.”

The 108,000-square-foot addition was designed by architects Hickok Cole with Arup providing mass timber and sustainable building engineering services. Opened in September, the scheme is also the “first high-rise overbuild timber structure in North America” according to the team.

Inside, the extension includes office and amenity spaces with 15-foot-high ceilings and 12-foot-high windows as well as 4,000 square feet of outdoor amenities including a rooftop terrace.

According to Arup, the scheme’s realization required engagement with “restrictive code requirements” in the United States pertaining to mass timber; restrictions which were recently loosened in the state of California. However, current IBC regulations adopted in DC cap the height of timber buildings at 85 feet.

As the proposed extension exceeded this height limit, the design team was required to demonstrate the scheme’s alignment with fire safety codes to the DC code authority. The process saw a particular focus on the extension’s structural connections, where a lack of fire-tested connections on the market led Arup to develop and test bespoke two-hour rated exposed timber connections to satisfy code authorities. The team also pointed to 2021 IBC standards that permit mass timber buildings of up to 12 stories.

“Mass timber is steadily gaining traction in the US market as more developers and designers recognize the cache and commercial potential of sustainably sourced and built projects, and more states and municipalities seek new ways to cut carbon emissions in the building sector,” ARUP said upon the scheme's completion. “As a renewable material, timber carries a significantly lower carbon footprint than conventional building materials, like concrete and steel. There is also a growing consumer demand for biophilic-inspired designs that take health and wellness into consideration by maximizing the occupant’s connection to nature.”

The scheme is one of several mass timber projects recently featured in our editorial. Last month, DLR Group and Hines unveiled details of Chicago’s first mass timber office building, while construction on SHoP’s 39-story hybrid timber tower commenced in Sydney, Australia.

In August, Herzog & de Meuron designed a mass timber mixed-use development in Austin, TX, while 3XN announced a mass timber campus expansion in Switzerland.