Megan Hall: Welcome to Possibly, where we take on huge problems like the future of our planet and break them down into small questions with unexpected answers. I’m Megan Hall.
Can you imagine going up to the top of your apartment building and enjoying a walk through some trees or doing yoga among some plants? These green roofs are popping up across many American cities. But, what are they exactly? And do they offer more than just some nice greenery?
We had Hamid Torabzadeh and Andrea Li from our Possibly Team look into this question.
Hamid Torabzadeh: Hi, Megan!
Andrea Li: Hello!
Megan Hall: So, what exactly is a green roof?
Hamid Torabzadeh: Basically, wherever we can grow plants such as vegetables, herbs, flowers, and fruits on top of a roof, that’s a green roof.
Andrea Li: There are many different types of green roofs – for example, you could build a vegetable garden or a small park.
Megan Hall: Sounds cool! And how are they actually built?
Hamid Torabzadeh: It can get complicated pretty quickly. But here’s the basic gist: a green roof needs a waterproof membrane, soil, and vegetation.
Megan Hall: A membrane?
Andrea Li: Yeah, the waterproof membrane is basically a layer of material under all the dirt that protects the actual roof from getting wet.
Hamid Torabzadeh: Above it, there’s soil, to help the plants grow and retain just the right amount of moisture.
Andrea Li: And then above this, of course, are all the plants!
Hamid Torabzadeh: To learn more, we went straight to the source and spoke to Mark Winterer, co-founder and owner of Recover Green Roofs.
Andrea Li: Recover is a company focused on the design, installation, and maintenance of green roofs.
Hamid Torabzadeh: Mark says there’s a range of options for green roofs, depending on how much weight your roof can hold.
Mark Winterer: Extensive is the lightweight, shallow system. Intensive is the heavier system that can support trees. And then semi-intensive, I call it the goldilocks. It’s not too heavy, it’s not too light, it’s the sweet spot.
Megan Hall: Got it. And why would we want these green roofs in the first place?
Hamid Torabzadeh: Good question. There are a lot of reasons. These roofs are part of a bigger strategy to make cities more green and livable.
Andrea Li: For one, they can make our cities cooler.
Hamid Torabzadeh: Research shows that green roofs can reduce air temperatures on the roof by up to 20°F.
Andrea Li: They can also potentially save costs by being more energy efficient.
Hamid Torabzadeh: This is because plants can act as natural insulators, reducing the need for AC in the summer and heating in the winter.
Megan Hall: So this could cut down on heating and cooling costs?
Andrea Li: Yes, but the amount of savings can vary depending on the type of roof.
Hamid Torabzadeh: One study found that a building with a green roof with smaller plants and no trees uses approximately 2 to 17% less energy than the typical roof during summer time.
Andrea Li: But, the building with the green roof was colder in the winter and cost more because the typical roof had better insulation materials.
Megan Hall: Got it. So it can get a little complicated.
Andrea Li: It absolutely can.
Megan Hall: But it seems like there are some serious benefits to these roofs, especially in the summer. Why don’t I see more of them?
Hamid Torabzadeh: The main challenge is the cost of installing a roof- they can be pretty expensive.
Andrea Li: And while these roofs offer benefits, they aren’t necessarily financial.
Hamid Torabzadeh: For example, Boston Medical Center has two rooftop farms installed by Recover on their hospital roofs.
Andrea Li: In 2024, the farms produced almost 10,000 pounds of produce, which they use to feed patients.
Hamid Torabzadeh: But, Mark says, the food Boston Medical Center grows isn’t saving them any money.
Mark Winterer: Profit wasn’t the driver on that one, there is data points on how much yield the rooftop farms are generating. It’s basically equivalent to the cost of what it would cost to to buy the that produce in the first place.
Andrea Li: In other words, green roofs can accomplish plenty of goals- cooling buildings, growing vegetables, and increasing green space. But, saving money usually isn’t one of them.
Megan Hall: Got it! Thanks, Hamid and Andrea!
That’s it for today. You can find more information or ask a question about the way your choices affect our planet, at askpossibly.org. You can also subscribe to Possibly wherever you get your podcasts or follow us on Instagram, Facebook, LinkedIn, or Bluesky at “askpossibly”
Possibly is a co-production of Brown University’s Institute for Environment and Society, Brown’s Climate Solutions Initiative, and Ocean State Media.
