Living roofs: a contribution to improving urban environmental quality

Green roofs or living roofs are roofs in which vegetation replaces conventional construction materials. What are its advantages and potential when it comes to improving the urban habitat?

Living roofs or green roofs are spaces in which concrete or sheet metal surfaces have been replaced by spaces occupied by grasses. It is not the objective of this article to delve into the technical aspects of their construction (for this purpose we recommend the book Green roofs. Execution, planning, practical advice, by Gernot Minke), but rather to focus on the benefits they provide in terms of environmental services and the potential solution they provide to some urban problems.

First of all, these are extremely efficient structures in terms of energy use. A well-made living roof is practically everlasting and does not require additional care, thus avoiding the expense of money and supplies for its maintenance; Once established, and if the correct plant species and a suitable substrate were used, it will not even need irrigation. Its insulating capacity prevents heat loss on cold days, greatly reducing heating needs, and during hot times it keeps spaces cool by preventing solar rays from directly impacting the building structure.

By retaining rainwater and slowly releasing fluids that exceed their capacity, they serve as relievers of the often collapsed storm drain systems, reducing the risks of flooding so frequent in some urban areas. On the other hand, they help control ambient humidity by evaporating water on dry days and condensing dew on humid days, which can also help reduce thermal amplitude. In addition to capturing moisture, the leaves of herbs retain dust particles and polluting particles suspended in the air.

Living roofs reduce heat in cities

The so-called “heat island” effect (a phenomenon that occurs in cities, where the temperature is sometimes up to 10ºC higher than in the surrounding rural areas, due to the absorption of heat by the asphalt during the day and its release. gradual at night) could be markedly reduced with the incorporation of green roofs, by reducing the exposed surface of thermoabsorbent materials. For those who are in the City of Buenos Aires, you can test this phenomenon by visiting the Faculty of Agronomy at night.

Of course, the fixation of carbon dioxide (the gas responsible for the greenhouse effect) and the release of oxygen is another of the benefits of these roofs, which should not be overlooked if we consider that most of the cities on the globe have a deficit of green spaces that compensate for their emissions, and if we consider the energy waste involved in lawn maintenance (mowing machines, agrochemicals derived from petroleum, etc.), the few existing parks end up becoming sources of emissions. Living roofs, when not mowed, can accumulate much more carbon than a landscape that is mowed regularly.

At the level of wildlife conservation, these roofs allow us to recreate degraded or disappeared environments (think of the practically extinct grasslands of the Argentine Pampas region, today replaced by monocultures, urbanizations and industrial parks), which is why we must put special emphasis on the use of herbaceous plant species native to the region in which we live (which are also adapted to the rainfall regimes of the area); This will also benefit local wildlife, which will be able to find food, rest and shelter in areas that are currently closed to them, in addition to the possibility of generating green corridors that serve as communication between natural areas. In this way, birds and insects (particularly butterflies) would receive necessary support during their migrations.

Although some authors do not recommend it, green roofs could serve for the development of urban agriculture, particularly for vegetable species with little root development and some aromatic herbs. However, we must not forget that living roofs are just that: roofs, and although they provide much more than a conventional concrete, tile or sheet metal roof, their main function is merely structural.

Another advantage in terms of comfort, apart from how warm or cool they may be, has to do with their insulating capacity from noise coming from outside.

Currently there are bills on the implementation of green roofs in Toronto (Canada), Mexico and Colombia, while some European countries do not have laws, but do have regulations that establish some parameters that must be taken into account to guarantee building safety, carried out by architecture schools. Some of the laws seek to force construction companies to include a certain percentage of living roofs in each new construction, which has already put several companies on the defensive, either due to the increased cost of construction, or due to the well-known reluctance that exists. to new paradigms and the comfort or distrust of academics in the building area.

Living roofs, greener cities

Going specifically, the studies available to date indicate that it would be necessary for at least one in every five roofs in cities to be green, to bring pollution levels to desirable parameters. It will be a challenge for the authorities to learn to address these events, and it would be an extremely positive gesture if they began with the landscaping of public administration buildings.

On an individual level, anyone who can carry out this endeavor in their own home will be happy to know the good they are doing, and they will be relieved to know that they will no longer have to worry about leaks. Those who are part of a vertical property consortium can also delve into the topic and present a proposal to their neighbors, or at least generate expectations about the possibility of converting a terrace that no one visits into a useful corner for nature and the environment. urban environment.