By Ju Yeon Jung

Spanish researchers are trialling a third-generation ecological roof using indigenous plants in a bid to make buildings more sustainable while retaining visual attraction.

According to a Science Daily report, researchers from the Polytechnic University of Madrid (UPM) have built a roof covered with plants and a watering system designed to optimise insulation effects.

The experimental roof constructed in Madrid was divided into 20 modules to identify which regional plant could elicit the best insulation effect against three criteria of the speed of growth, the density of the biomass and the aesthetical factor.

Professor at the UPM and co-author of the study, Francisco Javier Neila told the paper that plants that offer the best insulation were sedum or aptenia due to their thick leaves and resistance to frosts and heat.

He said the researchers had initially considered covering the roofs with a well performing plant then adding another plant to maximise visual appeal, but the combination proved to be infeasible as the stronger species would become predominant.

The groundcover model comprises a number of layers to effectively utilise rainwater and prevent leaks. A polystyrene sheet is inserted between each layer, which incorporates a sensor that gauges temperature and humidity levels for comparison with data held by an adjacent weather station.

“Roof areas with plants optimise better the heating and cooling of a building than a normal structure, regardless of how well insulated it is,” Professor Neila told the paper.

The concept of ecological roofs stems from the emerging ‘rurban movement’, which attempts to merge and harmonise urban and rural lifestyles in order to develop the most environmentally friendly and visually pleasing architectural techniques.

According to Professor Neila, ecological roofs effectively mitigate contamination in cities, by absorbing harmful chemicals including lead and cutting urban noises to three decibels. The roof’s absorption effects can also lower the temperature of heated metropolitan areas.

While the movement is gaining momentum in countries including Germany, Switzerland, the US and South Africa, he said high prices of groundcover development procedures were blocking more active development and deployment of the technology.

He told the report that government subsidies could encourage more developers to invest in the sustainable option, as seen in Germany where the situation was being resolved with tax benefits and council taxes.