Green roofs come in many forms, depending on the site, climate and owner intent. So what are those differences, and which is right for you?
Expecting green roofs to solve climate change single-handedly is like expecting any one football player to win the Super Bowl for his team. It’s a severe burden, and probably an unfair one.
However, neither would you dismiss a good player’s role in his team’s chances that year. We need all the tools we can get to find success.
(We’re not calling football players tools, by the way. Just FYI.)
But while we wouldn’t want to send them off on their own to do all the work, green roofs really are one of the best ways to address climate change. They:
- Insulate buildings so they use less energy
- Reflect sunlight, raising the planet’s albedo and keeping it cooler overall
- Help to fight the urban heat island effect, a phenomenon increases the temperatures of cities, which puts more demand on the energy grid and impacts human health
- Capture stormwater runoff and keep it out of streets at peak runoff times
- Give birds, pollinators and other critters a place to live
- Increase the number of native plants in our world
We could go on and on. (And on.) Instead, let’s assume we’ve convinced you of their amazingness and move right along to the question of which one is right for you?
Choosing between extensive and intensive green roofs is an important question in the decision-making process, so let’s take a look at the definitions and benefits of each.
Extensive Green Roofs
Think of your basic green roof, the one you might see on a government building across the way, six or seven stories in the air. With a multicolored carpet of creeping plants and little adornment, this is an extensive green roof.
Extensive green roofs utilize between 4 and 6 inches of growing media, or even less. Believe it or not, some green roof professionals can grow plants in as little as 2 inches of media successfully. (Ahem. We’re not bragging or anything.)
Because the media is shallow, plants usually top out at 16 inches tall. Any taller than that and the roots can’t support the height, so they tend to fall over. Of course, many plants – think sedums, those fleshy succulents with tiny leaves – are much closer to the ground.
The expectation for extensive green roofs is that they will be low-growing and low-maintenance. Note that we said LOW-maintenance, not NO-maintenance. Adopting the latter approach is the reason so many people end up needing green roof first aid down the road.
Like any other garden or living system, a green roof does need regular stewardship to protect plants, add nutrition and keep the environment balanced.
Typically, extensive green roofs strive for environmental benefits – cooling and stormwater management prime among them – over human amenity space. If you increase that planting depth by a foot or two, though, a whole new realm of possibility opens up.
Intensive Green Roofs
Green roofs with more than 6 inches of media are considered intensive. Their depth can range up to 2 feet or more, depending on the weight constraints of the roof.
Because they can accommodate much taller plants, and even shrubs and trees, intensive green roofs often become rooftop gardens, true amenity spaces indistinguishable from gardens on the ground – except for the view, that is.
Herbs, grasses, flowering plants and more abound on intensive green roofs, lending perennial beauty to formerly bare roofs and decks. (If you’re interested, you can read more about whether or not to get a rooftop garden here.)
Note you may see some green roof systems referred to as semi-intensive, which describes those with media profiles between 6 and 12 inches.
That extra 6 inches compared to extensive roofs may not seem like a lot, but you’d be surprised; it can significantly expand the water-holding capacity of the roof as well as the range of species that can grow there. If you want an amenity space, you will need at least a semi-intensive environment.
Want to talk extensive or intensive green roofs? That’s funny – so do we! We invite you to reach out to us today, and our friendly team will speed you on your way to realizing your dreams.