Green roofs do not finish taking root in Spain, where this type of sustainable facilities is little or nothing encouraged . Quite the opposite of what has happened for more than five years in France and Denmark, where it is required that all the roofs of new buildings be fully or partially used with some type of vegetation.
Of the total existing roofs in Spain, which the Sustainability Observatory estimates at some 350,000 hectares, 10% could be acted upon.
But Spain is light years away from reaching that figure. A recent inventory carried out by the Madrid City Council counted only 50 properties (21 are collective residential buildings and 29 single-family homes) with rooftop gardens out of a total of 108 buildings of different types that could be candidates.
Although there are cities that bid to champion change. This is the case of Barcelona, whose city council is promoting the generalization of green roofs through public tenders, the award being a subsidy for the execution of the works and their maintenance (which can reach up to 75% of the total budget).
Although landscaped roofs began to appear in the mid-90s, most of them are found on ground floor roofs, in common areas or on basement floors or garages in residential developments.
“Its penetration, on the other hand, is greater in singular office buildings, hotels, headquarters of large banks and, in general, in all those that opt for a sustainability certification such as Leed, Breeam or Verde, where much value is given to this type of facilities ”, states Gonzalo Causin, president of the Iberian Association of Waterproofing Manufacturers (AIFIm). This entity works so that the administrations legislate in favor of the installation of these covers.
They are essential to protect biodiversity, “but also to reduce the temperature in cities, where it has increased by more than 1.5 degrees on average due to climate change itself and the heat island effect”, explains Fernando Prieto, director of the Observatory of Sustainability
They can also act as a drainage control, preventing water leaks due to heavy rains or poor maintenance of the drains. In addition, they attenuate exterior noise and regulate the internal temperature of the building by acting as a thermal insulator, which helps to save between 20% and 50% on energy consumption for cooling, according to a study by the Polytechnic University of Valencia.
The slow penetration of green roofs is due to the complexity of the projects. And at its price. An extensive landscaped flat roof can be 10% more costly than a traditional one with similar properties, they calculate from the General Council of Technical Architecture of Spain (CGATE).
“The demolition and replacement of a green roof can cost between 125 and 150 euros per square meter, since we will need specialized labor and materials with better performance to ensure the tightness of the roof.
In the case of a sloping roof, the extra cost would be between 20% and 30% more compared to a traditional solution; around 170 and 200 euros per square meter ”, figure José Fernández, from the Technical Department of the CGATE.
Nor does the age of the housing stock help. Traditional roofs, both inclined and flat, have an approximate own weight of between 200 and 300 kilos per square meter.
“Intensive green roofs, which include large vegetation such as trees or shrubs, have a weight of between 300 and 1,200 kilos per square meter, so that, in the event of replacement, the structure would not be prepared to withstand this overload”, Fernández points out.
On the other hand, he continues, extensive roofs, with less pronounced vegetation, can weigh between 150 and 400 kilos per square meter, depending on the thickness, so it would not overload the structure. “We also have to be clear about how we design the green roof,
The big promoters are beginning to look at the green roofs although, for now, it is something residual.
“This element is part of a large set of measures that we are implementing in promotions within the framework of our sustainability strategy, which includes a battery of recipes to promote increasingly green residential projects,” says José María González Romojaro, director of Architecture and Sustainability of Aedas Homes. However, of the 120 developments under construction or recently completed, only three have green roofs.
In the race to advance, there are companies that are focusing their research on green roofs. Knauf Insulation and Verdtical have teamed up to develop the first smart green roof in Spain.
“Thanks to the sensors and actuators that are integrated into the installation, the roof will adapt to climatic changes during the day, even anticipating them to achieve greater energy savings”, explains Oscar del Rio, general manager of Knauf Insulation Iberia . A test reveals that the reduction in water consumption will be 75% compared to a traditional roof in a single year.
The Tecnalia research center is developing an application to identify the potential of implementing green roofs in a city. “We are also working on a line of solutions to increase the green surface of buildings, including roofs, in a simple and economical way, through interventions available to anyone, without involving large works”, they explain.