The office tower at One Post Office Square was built in 1980, across the street from a 950-car above-ground concrete parking garage that was generally considered to be an eyesore. The 41-story precast office tower was designed with some big ideas. An innovative structural system allowed for a floor plate with column-free corners, and the designers capitalized on that idea, creating extra jogs in the floor plan to define additional corner offices for executives. The heavy perimeter frame required for the scheme wasn’t conducive to full-height openings, but smaller windows were large enough for the private offices that lined the exterior.

Soon after the tower was built, Post Office Square itself was reimagined. The concrete parking garage was demolished and replaced with an underground parking facility, the site transformed into a park that has become one of the city’s most beloved green spaces.

The next step in the metamorphosis of the neighborhood is now underway. One Post Office Square stands with the lower half of its precast panels removed, structure exposed, and new curtainwall panels hung in their place. The building is in the midst of a massive transformation both inside and out, all to be completed while the tower remains partially occupied. The masonry façade is being removed, and in its place a custom high-performance glass wall will be installed. New, more efficient, and sustainable mechanical systems are being furnished. The building’s parking garage has been demolished, to be replaced with above-grade parking levels. These will feature a system capable of meeting current needs in half the volume through the use of automated sleds that slide the cars around each other, similar to the tiles of a child’s slide puzzle toy. This gain in efficiency will enable the building owner to repurpose more than 50,000 square feet of leasable area. Designed for future flexibility, the above-grade parking levels can be converted to conditioned interior space—which would be cooled or heated depending on the season—should parking demand continue to decline.

What precipitated this massive transformation?

In the 40 years since One Post Office Square’s construction, a lot has changed. Workplace planners have abandoned perimeter private offices in favor of open floor plans and flexible multifunctional spaces. New office towers are typically built with larger structural spans and taller floor-to-floor heights to accommodate this trend. Designers and developers understand that maximizing access to daylight, connection to the outdoors, and fresh air enhances wellness and productivity, and we try to design buildings accordingly. Floor-to-ceiling glass and expansive views are the norm in the new-build market.

How can older buildings compete in meeting the needs of a new generation of tenants?

Incremental updates to buildings as they age are always necessary. Components of mechanical systems are modernized; windows, replaced; and interior space, refreshed. One Post Office Square itself got a new glass lobby in 2008. This approach can be effective. But going all in on a deep retrofit can unlock value of a different magnitude. There is opportunity to provide a new life for an existing building, a new identity that can be experienced and understood from inside and out.

And then there’s the environment. With the climate crisis at a tipping point, it is imperative that we bring the best ideas in building technology to the construction industry, especially in cities, where, for the first time in history, more people live than not. But new construction can address only part of the problem. In fact, 50 percent of the buildings that will be in use in 2050 are already built.

It is crucial to the future of our planet that we reduce, immediately and drastically, our use of energy from nonrenewable sources. When we bring new life and value to an existing building, we are reinvesting energy expenditure in the form of embodied carbon. Reusing the existing steel and concrete superstructure of One Post Office Square is saving the equivalent of 14.5 metric tons of carbon dioxide compared to building a similar tower in its place. That’s the amount of carbon dioxide you’d produce if you drove to the moon and back 70 times.

It’s not easy to construct a tower today that defines a new benchmark in green technology, but it takes an even bolder vision to turn an underperforming existing tower into a sustainable building for the future. We argue that the next trend in urban headquarters should be investing in our aging buildings to give them a new identity and a greener life. It’s also the best move for the people who live and work in these cities. Metamorphoses such as these energize our downtown environments, both exterior and interior, and the experience of all who live, work, and play in our cities.

Perhaps in 40 years the deep retrofit of One Post Office Square will serve as a transformation paradigm in Boston and even beyond—one of many interventions that helps our cities thrive and our world stay healthy.