Denver’s Populus Says It's the First Carbon Positive Hotel in the US

A new hotel, Populus, broke ground near downtown Denver's Civic Center Park. According to developer Urban Villages, the property will be the first carbon positive U.S. hotel.

The 13-story, 265-room hotel is designed by Studio Gang, an architecture and design practice founded and led by architect Jeanne Gang. She's the recipient of many honors: Gang was called the World's Most Influential Architect by Time, is a MacArthur Fellow, and has a Louis Kahn Memorial Award and the Chevalier de la Legion d'Honneur, among other honors. Perhaps her most famous building is the Aqua Tower in Chicago, described by critic Paul Goldberger as an "undulating landscape of bending, flowing concrete, as if the wind were blowing ripples across the surface of the building." I was rather less enthusiastic, calling it a thermal and environmental nightmare.

After the Aqua Tower, Gang and her studio seemed somewhat chastened by the criticism and got serious about environmental issues in its own idiosyncratic way, whether reinventing thermal breaks (noticeably missing in the Aqua Tower) or sculpting buildings to manage sunlight.

Populus has a grab bag of green, with photovoltaics on the roof, heat recovery, "high thermal mass" from the concrete structure, and a high-performance envelope with Studio Gang's trademark solar control using a self-shading glass-fiber reinforced concrete (GFRC) facade.

The shape of the window is apparently "informed by studying the characteristic patterns found on Aspen trees (Populus tremuloides)," according to Studio Gang. The firm adds: "As the trees grow, they shed their lower branches, leaving behind dark, eye-shaped marks on the papery bark of their trunks."

Urban Villages describes some of the environmental measures taken to reduce the embodied or upfront carbon in the building. It has eliminated parking, which is an excellent method of reducing upfront emissions; it takes a lot of concrete.

"Populus will minimize its carbon footprint in the development stage using low-carbon concrete mixes, high-recycled content materials, maximizing structural efficiency, using fewer finish materials, minimizing waste, and more. This considers every stage of Populus, beginning with the origin of materials, as well as the carbon footprint of creating and transporting them."

Grant McCargo, Urban Villages’ co-founder and CEO, explains why. “To truly impact our earth, carbon neutral developments are no longer enough. Populus will be entirely carbon positive starting with its construction and continuing through to its ongoing operations while acting as a vibrant social center for locals and visitors,” said McCargo. “Not only will Populus be the country’s first carbon positive hotel, but it will be a stunning architectural landmark by Studio Gang that will forever alter Denver’s skyline and contribute to the architectural legacy of the entire Mountain West.”

"Carbon positive" is not a common term. In our review of all the terms used to describe the nomenclature of carbon, I concluded it meant the same thing as "carbon negative," which is usually defined as removing more carbon dioxide (CO2) from the air than was generated in the upfront and operating emissions. I liked it because, well, it's positive!

It first popped up in Australia and then Architecture 2030 founder Edward Mazria picked it up, with the best definition I can find, saying it's "where buildings, developments and entire cities are constructed to use sustainable resources, generate surplus renewable energy, and convert atmospheric carbon into durable materials and products."

Others are not so enamored of the term. In "What is the difference between carbon-neutral, net-zero and climate positive?," the consultants at PlanA write, "Carbon positive is how organisations describe climate positive and carbon negative. It’s mainly a marketing term, and understandably confusing—we generally avoid it."

Urban Villages has its own definition:

"Urban Villages is developing Populus to be carbon positive thanks both to its sustainable design and construction features as well as a substantial ecological effort offsite, including an initial commitment to planting trees that represent over 5,000 acres of forest – offsetting an embodied carbon footprint equivalent to nearly 500,000 gallons of gas and removing additional carbon dioxide from the atmosphere."

The developer continues:

"Urban Villages has calculated the carbon footprint of Populus and made a long-term commitment to be carbon positive. Instead of purchasing untraceable carbon credits as many others do, Urban Villages is accomplishing Populus’ carbon positive status by proactively planting and growing trees to make a tangible impact."

The people at Urban Villages are not environmental dilettantes and are doing fascinating work with an associated company, Biological Capital. But their approach here is going to be controversial, to say the least. As noted in an earlier post—Are Carbon Offsets Still a Thing?—it is complicated and they should not be considered a "permission to pollute."

While it is true that planting trees is a wonderful way to absorb CO2, it takes time for them to grow and do their absorbing. But there is a reason we prefer to call embodied carbon "upfront carbon emissions"—they happen now. They count against the carbon budgets that we have to stay below to avoid heating over 1.5 or 2 degrees Celsius (2.7 or 3.6 degrees Fahrenheit). Planting 5,000 acres is wonderful, but how long will it take? Who is protecting them? Who is certifying this?

It is so much more complicated than just grabbing the undefined term carbon positive. It has to be more than creating permission to pollute with a concrete structure and a concrete facade.

And we shouldn't be inventing or reinventing new terms anyway. British architect and sustainability expert Andy Simmonds tells Treehugger: "I think it’s unreasonable to not agree on a standardized methodology, metrics, and standardized concepts—carbon negative and carbon positive, etc. There’s no point in having conversations where we can’t agree on the very basic vocabulary concepts and units."

It is wonderful they have eliminated the garage and are using the best mixes of concrete and keeping their embodied carbon emissions as low as they can. But given they are still building out of concrete, please don't call it carbon positive.

As Passive House designer Andrew Michler told Treehugger about his own project built out of straw and wood and covered in solar panels:

"There isn't a carbon negative building in the world today, you will never know until it has finished its useful life and you know where the wood went, was it reused or burned or landfilled? Solar panels only last 25 years, and have a huge amount of embodied carbon. We will all be dead before we know if it is carbon negative."

It is certainly too soon to tell about Populus.