Story

Annex on 12th is an adaptive-reuse and new addition luxury apartment building at the site of the U.S. Department of Agriculture’s former Cotton Annex Building. Constructed in 1936, the historic Cotton Annex Building was used for the classification and standardization of cotton and tobacco until 2007. Construction on the project began in August of 2022 with the most complex activities taking place below grade and in the historic building. Situated over the orange/blue/silver line that runs between the Smithsonian and Le Enfant metro stops, the Annex on 12th building foundation had to be designed and constructed in close coordination with WMATA to ensure the building’s foundation was not applying pressure to the tunnel system. The team designed and installed rigid inclusion piles to transfer load away from the tunnel system. Additionally, 2 sets of chilled water lines ran through the site, between the GSA central plant adjacent to the project and all the Smithsonian buildings. A complex and coordinated plan to relocate the larger set of lines below the foundation commenced in October, while the smaller set was left in place and built into the foundation of the project. This work was executed with little margin for error as it had a dropdead completion date in late spring of 2023 to ensure it would not impact the Smithsonian’s ability to provide air conditioning to its spaces. Above grade, the new design required extensive work to historic building to transition it from an office space to 92 residential apartments. Chief among the primary challenges to reposition the building were all the window cut outs that were now required on the façade. The exterior skin of the existing building was a 3 wythe thick brick load bearing system which would require extensive steel support to install the new windows. Where the old windows were maintained due to historic preservation requirements, every functional window sash was removed, tweaked back to a plumb/true condition and reinstalled. Every pane of glass in the historic windows to remain was removed and upgraded with a more energy efficient substitute. Inside the building, the elevated decks were a waffle slab design, which new waffle supports and beams overhead where new shafts were required or the existing concrete was deemed to be too degraded due to age. On the new construction portion of the project, work was more straightforward, but closely coordinated. Due to differing floor heights between the new and old building, pedestrian access between the 2 occurs on only a few floors. While most of the amenities are located in the historic structure, the new building rooftop pool deck and the upper floor units facing north provide stunning views of downtown DC and the mall. The project achieved its TCO in November of 2024 and began leasing in December. In totality, Annex on 12th has more than 24,000 square feet of combined indoor and outdoor amenity space and 562 units.