One of the concerns raised by apartment owners wanting to create gardens on their roofs is whether their buildings’ structural specifications can stand the weight of the soil required, especially when it is watered. Installers of these «greenroof» systems, of which there are now a considerable number in Greece, are on hand in Kotzia Square this week to answer the public’s questions and demonstrate just how easy it is to insulate roof terraces from heat in the summer and from losing heat in winter. The «Green Rooftop – Blooming Balconies» exhibition, organized by the City of Athens, runs until Monday, May 12. Manufacturers from several firms are on hand to explain the systems and show examples. There are various types of greenroof systems. The lighter green roof systems, known as «extensive,» weigh from 80-120 kilos per square meter, and most conventional buildings can withstand a weight of up to 200 kilos per square meter. The extensive greenroof system consists of a lightweight rooting material measuring 8-15 centimeters. These are better for roofs without easy access that do not require frequent maintenance or watering, and are usually planted with drought-resistant ground cover, including the hardier variety of grasses. The heavier weight systems (semi-intensive and intensive) allow for a more varied planting and taller plants that need deeper soil and weight from 100-270 kilos per square meter. Apart from providing a garden area for residents to enjoy, the benefits of greenroofs include a reduction in sound pollution (up to 8 decibels) and in the dust and smog in the microclimate around the building. The life expectancy of the building’s waterproofing system can be extended by up to 40 years as the turf and plants protect it from ultraviolet radiation, hail and extreme temperatures. A greenroof can reduce heating costs by two liters of fuel oil per square meter a year. It also reduces rain runoff by 10-50 percent. The drainage layers are made of rubber, polyethylene and expanded polystyrene and the planting medium is a mixture of pure recycled clay bricks with humus. Meanwhile, more landscape designers are being trained in the use of greenroof. Landscape architecture students have stands at the exhibition displaying models of their designs.