Green Roof Design

Green roofs will be a big part of our sustainable city, our city of the future. In fact just about all buildings will have some green roof design elements incorporated in them. There are many positives and no negatives. It’s like comparing a little slice of forest or meadow with a parking lot. You won’t get much of an argument for the benefits or the latter.

What exactly is a green roof?

City Hall - Chicago

The overall idea is not a complex one, a green roof is simply a rooftop that have been covered in three layers: a) a membrane to keep a separation between the moist organic material from the underlying roof, b) a soil component, typically a mixture of organic and inorganic compounds, c) vegetation and amenities including everything from a simple grass meadow to a lush forest with ponds and pathways.

There are two distinctive types of green roof design, extensive and intensive. An extensive roof is one that will lean to the lighter side and meant to be home to bugs, not people. This type of green roof would have a lower profile soil level, anywhere from eight inches to as little as an inch or two. The vegetation might resemble a mountain grassland or plateau with a mixture of shrubs and grasses. An intensive design is one that is created for human usage. The soil level will be deeper to accommodate a greater variety of vegetation. Anything from grasses and mosses up to full grown trees and hedges. The soil level in this type of green roof design will have less non-organic material, at least 50% organic and the depth will be much greater, anywhere from eight inches all the way up to fifteen feet (to accommodate trees and ponds). This type of area will often be well traffic by people and incorporate features such as gazebos, walking paths, benches and more.

The big picture benefits of a green roof include the following:

  • Reduced heating of the surrounding area
  • Improved humidity levels
  • Air Purity
  • A home to a thriving community of insects and birds
  • Economic gains
  • Psychological gains

As anybody who has walked across a hot paved surface in the summertime knows that the grass across the street feels nice and cool. Surfaces like concrete and asphalt give off a ton of heat. A typical city may run anywhere from 2 to 10 degrees hotter than a surrounding area. A nice meadow or grass rooftop helps to cool down the immediate area. A whole city of green roofs would be much more comfortable in the summer.

Airborne dust particles and toxins are absorbed by the vegetation on a green roof. It’s acts like a giant filter. Even a small patch has an effect on air quality.

There are many economic gains to be had with a green roof project. There are immediate gains in that a roof will generally last much longer due to it not being directly bombarded by the sun’s harsh rays. A heavy, moist surface will protract the lifespan, reducing the costs of roofing materials. There can be immeasurable indirect benefits as well. Everything from lower A/C costs due to the thermal mass effect (lower heating in winter as well), new jobs created to maintain and manage the areas, and a general improvement in the state of the building thus increasing its value.

By far the greatest impact to a city that incorporates green roof design is its effect on moral. Humans feel better when surrounded by life/nature. Be it an aquarium, plants in the living room or a rooftop meadow, people will be in a better mood when removed from a cold, concrete, lifeless environment. More and more modern city buildings are incorporating vivariums and green spaces; adding a green roof on an otherwise unused space takes this to the extreme. You only need to look at the joyful expression on the face of anyone that experiences a lush garden ten stories in the air for the first time. The often have an incredulous look about them and even the stoutest will have a smile on.

Is a green roof expensive?

Not terrible but it depends on a few variables, namely what type of roof and how large. A small extensive type may cost as little as $10 to $20 per square foot while an intensive roof may be closer to $20 to $40 per square foot. The price will lower (at times quite a bit) when you start talking about much larger projects.

I feel it is fitting to end with remarks from an architect that will be feature quite a bit on this site, Friedenreich Hundertwasser:

The true proportions in this world are the views to the stars and the views down to the surface of the earth. Grass and vegetation in the city should grow on all horizontal spaces – that is to say, wherever rain and snow falls vegetation should grow, on the roads and on the roofs. The horizontal is the domain of nature and wherever vegetation grows on the horizontal level man is off limits; he should not interfere. I mean taking away territories from nature, which human beings have always done.

grass covered houses

I’ll finish things off with a few more images of some spectacular green roofs and a promise that we’ll write up an article shortly about this fist image, The California Academy of Sciences by Renzo Piano, one of the coolest buildings (green-roofed or otherwise) that I’ve come across. This and the biodome in Montreal will be examples of indoor nature preserves that will be in our city.

California Academy of Sciences by Renzo Piano

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