The life expectancy of a "naked" flat roof is only 15 to 25 years, even with professional installation. This is due to the physical, chemical and biological stress on the roof skin/ waterproofing over the years. Temperature differences of more than 100 °C during the year and 60 °C over 24 hours are not unusual. UV-radiation and high Ozone ratios accelerate the ageing process of the waterproofing; which results in, material fatigue, shrinking, crack formation, and leakage. Green Roofs provide protection for the waterproofing. The vegetation layer buffers the temperature stress during summer and winter, and temperature differences of, 35 °C during the year and 15 °C over 24 hours are not usually exceeded. In addition, the Green Roof creates a protection layer for the waterproofing in case of mechanical damage like hail, wind, vandalism, and fireworks.
Green Roofs reduce sound reflection by up to 3 dB and improve sound insulation by up to 8 dB. This is important for people who live near airports, noisy discotheques, or industrial parks. Additionally, electromagnetic waves from transmitting stations can be effectively shielded by the vegetation layer.
Green Roofs can be regarded as additional thermal insulation, thus, reducing
the use of primary energy. This is a well known economic benefit; however, in
former times it was not possible to quantify this effect and integrate Green
Roofs into the building energy balance.
This gap was closed at the beginning of the nineties when special Green Roof build-ups were officially credited with thermal resistance values (R-Values) by the German Institute for Construction engineering. Depending on the original thermal insulation, an amount of 1 - 2 L/m2 of oil can be saved with this additional thermal insulation.
During the summer months Green Roofs reduce indoor temperatures through transpiration. According to tests from Drefahl (1995), the microclimate of an apartment underneath a Green Roof is comparable with one on the base floor. The typical overheating of attic flats in summer can be avoided with vegetated roofs; therefore, decreasing the use of air conditioning and energy consumption.
Green Roofs offer various possibilities for usage, including: natural refuges for insects and plants, recreational roof gardens, roof cafés, and sporting areas. If the technical and construction requirements of the building are met, there are virtually no limits for landscape designs with perennials, small trees, terraces, or gardens. Due to the utilization of the roof property, the building owner can save costs from purchasing additional land at ground level. A gorgeous view, fresh air, and privacy are also included in the price. Roof gardens increase the work environment enormously and offer nearby recreational areas, even in conurbations.