Dachbegrünung und Photovoltaik

Green roofs and solar panels

Green roofs are like air conditioning

Dense concrete jungles change the climate: urban heat islands arise because concrete and asphalt heat up much more than green areas. Cooling by evaporating rainwater is missing. Marco Schmidt from the Institute of Architecture at the TU Berlin sees a way out of this vicious circle in the greening of roofs and facades. Instead of letting rainwater run away unused, green roofs store it so that it can evaporate on hot days: "This is the easiest and cheapest way to improve the city climate," says Schmidt. The landscape planner, who specializes in ecological building, has been researching the positive effects of green roofs for years: "In our measurements, we have shown that they convert the majority of solar radiation into the evaporation of water". While a bitumen roof heats up to 70 degrees Celsius in summer, green roofs stay significantly cooler at around 30 degrees Celsius. In addition, a green roof ensures a longer lifespan for the roof covering as well as better thermal insulation and thus lower heating costs in winter. In summer, on the other hand, it shields the building from the heat.

Two systems: intensive or extensive?

Intensive green roofs are when the thickness of the earth substrate is 20-60cm, and perennials, hornbeam hedges and small trees can be planted. Extensive green roofs are the economic option, with some added advantages. The roof structure and thus the statics are designed much smaller and the ground layer is only 8–15 cm thick. There is no irrigation system. Suitable, drought-tolerant plants must be carefully selected. Alternatively, there are ready-made mixtures of seeds and sprouts from various types of stonecrop. Small, but fine, including yellow and white stonecrop, fragrant thyme, Dianthus deltoides, Jasione laevis and flowering mountain chives – blooming vibrantly and requiring little maintenance. (Text taken from the brochure „Moderne Unternehmen im Einklang mit der Natur“, Hrsg: LUBW Landesanstalt für Umwelt, Messungen und Naturschutz Baden-Württemberg, Karlsruhe 2013)

Principle sketch extensive and intensive greening, Optigrün


A 15cm green roof is able to store approx. 50% of precipitation, thus relieving stress on the sewer system and reducing wastewater fees. Green roofs contribute to water conservation, soil and microclimates and are therefore ecologically recognized as a preservation measure.

Flat roof and pent roof

Flat roofs are the norm, but pent roofs with an incline of 20 to 30 degrees can landscaped equally as extensively.

Green Roof and Solar Panels

At first, they seem to contradict each other. However, in a research project, it was demonstrated that evaporative cooling of vegetation increases the efficiency of photovoltaic systems, like a synergy effect. (Garden + Landscape 12/2009)

Chicago is fighting global warming

In the United States, heat waves are becoming increasingly stressful. In a climate action plan, the Chicago City Council decided on more energy-efficient public buildings and accelerated approval procedures for "green" projects. So far there are 650,000 m² of green roofs in the city. (Die Zeit, 24.11.2011)

Source of information

Modern companies in accordance with Natur Leitfaden für ein naturnahes Betriebsgelände Hrsg: LUBW Landesanstalt für Umwelt, Messungen und Naturschutz Baden-Württemberg, Karlsruhe 2013