A green roof, a nordic tradition , with present use with germans as leaders, is a roof of a building that is partially or completely covered with vegetation. There is consensus that a growing medium, planted over drainage, an irrigation system and a waterproofing membrane on top of a building is a green roof. Container gardens on roofs where plants are maintained in pots may produce the same benefits and represent very beautiful instances of roofs covered by green. But there is contention if the expression green roof also includes roofs looking green by this way. There is no contention that covering streets with treetops does not make green roofs as some Brazilians say.
Usually we find in the literature, conventional or in electronic media, lists of green roof benefits not discriminating the benefit nature, if relative to Adaptation to Global Warming, if connected with mitigation.
Lets display these relations.
The benefit which most emphasis is given goes about the cool relief, on a hot day, for the offices immediatly under the roof, given to the high thermal insulation capacity of the green roofs. To those with air conditioning the smaller absorption of heat by the structure of the building is translated into smaller electricity bills. This is so because the waterproofing membrane, the drainage system and the growing medium work as insulators. The vegetation leaves reflect more than the ordinary tiles, absorbing less solar heat. But there is more. Most of the solar energy that the leaves absorb are not transformed into heat as the tiles do. They use this energy to their metabolic work, and more important yet, to bring water from the soil (their growing medium in the green roofs case), which evaporate keeping down their temperature. To keeping down the roof temperature in a hot day, when the hot days are forecasted to be more frequent and more hot, the green roofs works as an Adaptation to Global Warming effect, appropriated by the building users, mainly by those directly under the roof.
On hot or cold days the vegetation leaves, the growing medium, the drainage system and the waterproofing membrane compose a sound absorbtion system protecting the ears of the building occupants. This is a benefit appropriated by the building users, also mainly by those directly under the roof.
To the building owners there is a benefit related to the life span of the building and to its maintainance costs. The green roofs reduce the expansions and contractions of concrete roofs just the place in the buildings where those variations are more severe, mainly because they have sinergy with deformations caused by winds that bend the structure in a way as more accentuated as more high one is. As the winds are forecasted to be more strong with the Global Warming, this property of the green roofs work as an Adaptation to Global Warming that benefit the building owners.
Now two Adaptation to Climate Change effects brougth by the green roofs that work as public goods at a county level. By decreasing the solar thermal energy absorption by buildings, also decrease the thermal energy dissipated in the air, thus decreasing the inconvenient heat island effect. In addition green roofs decrease the water flow, thus helping to prevent floods.
Finally, in this rol that is far from being exhaustive, one may say that as all vegetation, green roof absorb carbon dioxide. It produces, then, a mitigation effect. It is a public good at all mankind level, benefiting all people in this moment and as far way in the future as the human horizon can see.
It is important to notice that as the problem of heating the roof structure of buildings is literally of all latitudes, the benefits of green roofs can be harvested in literally all latitudes. But as the conditions vary substantially betweem different places, and native vegetation is recomended, there his for resaerch about them in all latitudes.
For all this, it seems that green roofs should be universally incentivated.
In Brazil there are resaerchs about green roofs going on the Southern states. But the other area, covering the majority of the extension of the country resaerch on this topic is missing. So are unkown to be research going on other latinamerican countries. And there is no information about incentives to green roofs on this part of the world.
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