It’s the concept of greenroofing, and it’s explained in great detail at Greenroofs.com.
Basically, greenroofs are vegetated roof covers, with growing media and plants taking the place of bare membrane, gravel ballast, shingles or tiles. The number of layers and the layer placement vary from system to system and greenroof type, but at the very least all greenroofs include a single to multi-ply waterproofing layer, drainage, growing media and the plants, covering the entire roof deck surface.
What are the advantages of greenroofing? There are ecological, economic, aesthetic & psychological advantages.
Here are some of the economic advantages:
Overall building energy costs can be reduced due to the greenroofs’ natural thermal insulation properties – structures are cooler in summer and warmer in winter. The urban “heat island” effect can also be greatly reduced since vegetative roofs reduce ambient air temperatures. Therefore, less electricity costs are expected from lower a/c and heat usage.
According to an article from the Environmental News Network, “a 3- to 7-degree temperature drop translates to a 10% reduction in air conditioning requirements. For a one-story structure with a green rooftop, cooling costs can be cut by 20 to 30%.” The Weston Design Consultants recently conducted an energy study for the city of Chicago which estimated that it would be possible to save $100,000,000 in saved energy annually with the greening of all of the city’s rooftops. The bottom line is that “Peak demand would be cut by 720 megawatts – the equivalent energy consumption of several coal-fired generating stations or one small nuclear power plant.”
There was an article I read that a hotel in Canada was using the rooftop as a garden for growing herbs. Not so much as a green roof, but it probably help and it also allowed the restraunt in the hotel serve better meals as the herbs are fresh not dried.
In China many of the newer apartment buildings have gardens and trees growing on the roof. They also hang laundry and spend family time up on the roof. I am not sure if it is having an impact on the usage of electricity, but it does help them socially.
In other parts of the world I have seen some very strange housing. In Australia there are underground houses the uses the dirt and rock to insulate the house from the extreme heat of the Australian desert. Many of the houses along the Pacific uses open wall architecture to allow the wind to cool the houses. On the otherhand I have seen a university in the same area build a building totally enclosed and set the thermostats at 63 degrees because that woudl save money (On the continental United State during winter.) I sometimes wonder if that is higher education.