The simplicity of this question can lead to a variety of answers related to environmental, economic, societal, existential aspects. However, they all lead to the BENEFITS of green roofs. In other words, your green roof:
A green roof protects the roofing material from external influences such as sunlight, rain, wind, and temperature fluctuations. The durability is increased and the performance of the waterproofing and plaster is improved as the vegetation eliminates the influence of UV rays, protects against mechanical damage, and improves the temperature-humidity regime. European roofs can last between 30 and 50 years. A green roof extends the life of your roof 2-3 times. You will certainly recover the investment in your green roof within 5 to 20 years.
Sustainable drainage is an important component of any building as a way to counter flooding in the event of heavy rainfall. Unlike conventional roofs, which are designed to discharge rainwater as quickly as possible, green roofs absorb rainfall by storing water in the plants, substrate, and drainage layer. It has been estimated that a green roof retains rainwater from 40-80% of the annual rainfall and up to 100% when an irrigation system is installed. The effect is particularly large when green roofs are more in number and are combined in a green system. The load on the sewerage system is significantly reduced and rainwater is also treated. All this helps to stabilize the groundwater level, the peak load on the sewerage system is reduced and the risk of flooding is minimized.
The green roof increases the thermal performance and improves the energy efficiency of the building. Roof greening, depending on the thickness of the vegetation layer and the type of greenery, improves thermal insulation by up to 40%. The insulating effect of 6.5 to 18 cm thick elements of a roof landscaping package can be compared to the effect of conventional 2.5 to 6.5 cm thick insulation. For a single-family house, roof greening can reduce the gas demand for one heating season by 100 m3. The energy-saving effect of landscaped buildings is better during the hot months. Air conditioning consumption can be reduced by 75% in summer. Plants absorb and reflect a high percentage of the sun’s energy and therefore reduce the roof temperature in the summer while helping thermal efficiency in the cold winter by providing heat inside, which in turn leads to energy and financial savings. In turn, this results in reduced CO2 emissions of 215 kg/m2 per year.
Densely built-up urban areas and urbanized spaces experience persistently higher temperatures, which is referred to as the Urban Heat Island (UHI) effect. Higher temperatures at the ground surface and in the air layer in contact with it add to the heat load of urban populations, increasing temperature stress, especially during the summer months. The urban heat island effect occurs in cities, where dark building roofs, black asphalt, and concrete pavements concentrate the heat of sunshine. The temperature in the city rises to 12°C. This causes public health and well-being problems as well as a significant increase in energy consumption and associated greenhouse gas emissions. Green roofs can help reduce the urban heat island effect, considered one of the key contributors to climate change. They provide an additional positive influence on the climate near your building and the temperature in the city. Overall, this means a 3°C reduction in urban temperature thanks to green roofs.
Hard surfaces reflect sound instead of absorbing it. Green roofs can act as sound insulation, absorbing and reducing noise levels by 2-12 dB. Improving sound insulation as a property of roof landscaping is particularly important for one- and two-story buildings as well as for lightweight roof structures.
Green roofs can increase biodiversity and create habitats in large settlements that are not usually hospitable to wildlife. Herbs and perennials on green roofs have an important ecological role as replacement habitats, creating alternative habitats for bees, butterflies, insects, and birds in urban areas.
Green roofs support a wide range of plants – succulent sedums, flowering perennials. All this vegetation beautifies the building both from the outside and inside. Having a view or access to natural vegetation (e.g. on a green roof) provides a positive impact on psychological well-being. There is plenty of evidence that this can increase staff productivity and more – green spaces can also help patients recover faster.
Solar panels work efficiently up to 24°C and 25°C. When ambient temperatures exceed these levels, PV panels lose efficiency. Green roofs, through evaporation, can lower the ambient temperature, which means solar panels operate more efficiently, thus generating more power. In warmer climates, PV panels take advantage of the cooler air created by green roofs to maintain or increase their efficiency. It has been estimated that PV systems improve their performance by up to 6%.
The release of carbon dioxide is one of the key contributors to global warming, which is why governments are tasked with meeting the EU’s stringent 2030 targets for reducing levels. According to scientific data, over 43% of total CO2 emissions come from buildings – cooling, heating, etc. Green roofs reduce the need for air conditioning while helping to use less heat in winter. Plants and vegetative carpets on the green roof filter particles from the air and convert CO2 into oxygen. They also help reduce the amount of dust in the air. To be more specific, green roofs ‘trap’ dust and air pollutants – PM10 ranges between 0.42-9.1 g/m² per year. With a green roof, you contribute to cleaning the air and saving nature.
Greening buildings and creating green roofs also brings benefits as an economic approach. As green roof and façade technologies grow in popularity around the world, job opportunities are being created in all sectors of the market, from raw material importers to manufacturing, transportation to retail, and from design to construction. Opportunities for research and innovation are provided. The emergence and application of this technology create new jobs for the benefit of the local economy.