Sadie Denson, Programs & Services, GBI
Located at 1909 K Street NW in the heart of Washington, D.C., the Millennium Building, a 12-story, 235,000-square-foot commercial office space, has become a cornerstone of the Tower Companies’ long-standing commitment to high-performance buildings and environmental leadership. As the first Journey to Net Zero™ certified building in Washington, D.C., and with a distinguished history of ENERGY STAR certifications and cutting-edge sustainability upgrades, the highly acclaimed structure stands at the forefront of Tower Companies’ strategic portfolio-wide effort to achieve net zero carbon and energy by 2047.
The Millennium Building, Washington, D.C.
Originally built in the 1960s and modernized in 1999, the Millennium Building has undergone continuous upgrades to match, and often exceed, the sustainability benchmarks of the time. Its transformation has been both technical and cultural, embedding efficiency into day-to-day operations. The building includes amenities such as a rooftop terrace with an herb garden, a fitness center, and an 80,000-square-foot parking garage, but its true value lies in its high-performing infrastructure and operational efficiency.
With an Energy Use Intensity (EUI) of just 43.5, well below the national median for buildings of its size, and over 15 consecutive years of ENERGY STAR certification, the property showcases how investments and upgrades in legacy assets have measurable results.
The Tower Companies enrolled the Millennium Building, certified in 2023 and 2025, along with 15 other buildings in their portfolio, in the Journey to Net Zero program. Unlike one-time certifications, the JNZ program emphasizes portfolio-wide decarbonization as an iterative process with updates and progress made between assessment periods. This allows Tower to plan strategically for equipment lifecycles, optimize ongoing operations, and track emissions reductions.
The JNZ framework evaluates carbon emissions and energy performance, benchmarking buildings against science-based targets while supporting owners through a third-party assessment. The third-party assessment model ensures integrity and transparency, providing a credible pathway for achieving net zero outcomes.
The Millennium Building’s path to net zero has been marked by strategic upgrades and operational best practices. Over the past decade, Tower has replaced major mechanical systems, including HVAC, with electric alternatives, laying the foundation for a fully electrified future. In 2014, the building became one of the first commercial properties in D.C. to install rooftop solar panels, starting with a 35 kW array. In 2024, the system was expanded to 125 kW using a racking system that maximizes rooftop coverage, providing daytime offsets to grid energy use and supporting peak load reduction.
125 kW rooftop solar, using a racking system that maximizes rooftop coverage, providing daytime offsets to grid energy use and supporting peak load reduction.
Monthly engineering meetings paired with real-time energy data empower the building team to fine-tune performance, manage HVAC loads, and participate in demand response programs that reduce strain on the grid. The building’s electric demand is met entirely through renewable energy purchases. Additionally, Tower offsets 100% of its carbon footprint with carbon offsets and renewable energy certificates (RECs), demonstrating a commitment to both reduction and accountability. Continuous improvement projects have targeted building controls, aligning energy consumption with occupancy patterns, and supply-side dynamics, to ensure the building always operates as efficiently as possible.
The Tower Companies’ commitment to sustainable operations is bolstered by their participation in the U.S. Department of Energy’s Better Buildings Program and collaboration with experts from Lawrence Berkeley National Laboratory. These relationships have provided insights into national best practices and allowed Tower to benchmark its efforts against peer organizations. The ENERGY STAR Portfolio Manager tool is another cornerstone of Tower’s decarbonization work, serving as a consistent metric for evaluating energy performance across its portfolio.
Tower offsets 100% of its carbon footprint with carbon offsets and renewable energy certificates (RECs)
The Millennium Building serves as a proof point within the broader strategy of the 16 Tower properties now engaged in the JNZ program. Seven additional buildings have achieved Recognition status, and eight are currently in the program’s Onramp stage. Together, they reflect Tower’s portfolio-wide approach to decarbonization.
Illustrating what’s possible when long-term ownership, smart planning, and third-party assessment intersect, the property stands as both a technical success and a leadership story. It serves as a primary example to the commercial real estate sector on how to leverage building performance to meet climate goals while delivering returns through efficiency, resilience, and enhanced asset value.
As the commercial sector confronts the urgent challenge of reducing emissions from the built environment, responsible for nearly 40% of global carbon emissions, the Millennium Building offers a real-world example of how strategic retrofits and data-informed operations can transform aging infrastructure into climate assets.
Learn more about The Tower Companies efforts to decarbonize it’s building portfolio