Many years ago, I was in a design meeting for a tall building we were working on and I brought up the idea of planting greenery all the way up the tower. You know, something like the Bosco Verticale in Milan.

But after I said this, our landscape architect looked at me and simply said, "No, it doesn't work, not in our climate." And that was it.

Of all the people in the room, I thought I could get the landscape architect excited about this suggestion, but nope. It got immediately shot down, and for good reason.

The greenery would be dead here in Toronto for not an insignificant part of the year, and the additional dead loads created by water-saturated soil and structural planters raise questions about whether it's the most sustainable way to build tall buildings.

But there are climates where green towers make a lot more sense, namely in places like Brazil. In fact, São Paulo rewards developers for integrating features such as green facades.

Here's a specific project example: The Rosewood Hotel in São Paulo, designed by Jean Nouvel. The 25-storey tower features an extensive lattice system on its exterior that, over time, is expected to fill in with greenery from adjacent roof gardens.

The hotel opened in 2022, and street view images from 2024 reveal that it still has some growing to do, but clearly it's a popular idea. I was just in the wrong city.

Photos via Rosewood São Paulo

A residential community in China's Shanxi province has been in the news recently for a cooling system that sprays mist from its rooftops to lower the surrounding surface temperatures. Here's a video in case you missed it.

As I understand it, this evaporative cooling technique can lower nearby surface temperatures by 5°C to 8°C within minutes, and it uses significantly less electricity than air conditioning.

This, by the way, is the same scientific principle behind how sweat cools human skin. We sweat, the sweat then evaporates, and in the process it helps to lower our body temperature.

But the obvious question here is: Doesn't this waste a bunch of water?

Generally, these systems tend to rely on (1) very fine mists of water (so as little water as is necessary) and (2) collected rainwater and/or recycled greywater. The general idea is to just lower surface temperatures so that less air conditioning is needed.

Next, it becomes a question of electricity saved vs. water consumed. A study done on a 5-storey apartment building in Osaka found that outdoor misting reduced the building's cooling loads by an average of 36%, and from a financial standpoint, the value of the electricity saved was greater than the cost of the water consumed.

Importantly, it also helped reduce the overall urban heat island effect in the area. The amount of waste heat trapped in the nearby city streets decreased by over 60%.

Hotter streets are a byproduct of air conditioning because the cooling process effectively sucks heat out of interior spaces and transfers it outside. Misting counteracts that and also reduces peak AC loads.

So, as wild as these sweating towers may appear online, there is some logic behind them.

Cover photo via this Twitter post

In recent years, a new housing typology has emerged in London that involves the practice of building penthouses on top of existing buildings. Here's a post I wrote back in 2021. This is not the simplest way to build new housing, but there are clear benefits. New housing does get created (however incremental it may be), existing buildings are preserved (which is positive from a sustainability perspective), and housing complexes with maintenance and repair needs have a new way to raise money.

Here's a penthouse example completed in 2023 that was designed by David Kohn Architects for Baylight Properties.

What I think I glean from the plans is that the building's existing elevator and exit stair were extended up into the new penthouse space, and a new internal stair was added within the penthouse. This would have required a great deal of coordination to minimize disruption to the existing building. Presumably, they built the new shaft extension, got everything ready, and then shut down the elevator for the shortest possible period of time to switch everything over. The existing building is only 4 floors, so it's not the end of the world.

As an aside, Baylight Properties has other rooftop projects underway, including the Sky Houses at Ransome's Dock. I also very much appreciate the ethos of the firm. On their website, they clearly state: "Our overwhelming interest has been to combine the harsh realities of business with all the benefits good architecture bring." It sounds a lot like how we think about our approach at Globizen. Maybe it's time we also start looking at some rooftops.

Project photograph by Will Pryce via David Kohn Architects

Plans from David Kohn Architects