Why Grow Plants on Roofs?

In recent years, more and more governments and private companies around the world have been investing in green roofs. The analytical company Reports and Data forecasts that the global market for green roofs will grow by 17.2% from $1.14 billion in 2019 to $3.79 billion in 2027. Experts are confident that plantings on building roofs make people's lives more comfortable and safe, and also help solve many of the problems facing modern cities. In Russia, this market is developing at a slow pace, but it is possible that the situation will change soon.

How a green roof works

There are two main types of roof greening: mobile (containerized), when pots with plants are placed on roofs, and stationary. A stationary green roof is prepared with a special environment for growing plants: a water-proofing and root-protective layer, drainage, a filtering layer, such as geotextile fabric, and a soil substrate.

Depending on the height of the substrate layer, stationary greening can be extensive, semi-intensive, and intensive. Roofs with extensive greening have a soil layer thickness of 90 to 150 mm. They are planted with mosses, lichens, and grasses that do not require serious care and have a high regeneration capacity. This type of greening is also suitable for sloping roofs. With semi-intensive greening, the soil layer thickness is 150 to 300 mm, and herbaceous plants and small shrubs grow on it. Intensive greening with a soil layer of at least 300 mm is suitable for roofs that can withstand high loads. It involves growing large shrubs and trees that require constant care: watering, fertilizing, and weeding. Plants must be selected taking into account the season and climatic characteristics of the region. Benches and tables for picnics, vegetable gardens, sports and children's playgrounds, and walking areas can be installed on green roofs.

Why cities need green roofs

One of the main advantages of green roofs is that they help prevent flooding during heavy rainfall. Rainwater accumulates in the substrate and then is absorbed by plants and returned to the atmosphere through evaporation. According to estimates by the Canadian non-profit organization Green Roofs for Healthy Cities (GRHC), green roofs can retain 70-90% of precipitation in the summer and 25-40% in the winter. As a result, the load on the storm sewer system is reduced and it can better cope with the drainage of water. Rainwater can be collected in reservoirs and used for technical purposes, which will help to reduce the amount of water used.

Concrete and asphalt surfaces disrupt the energy balance in the city, which is why the temperature there is often higher than in the suburbs. This phenomenon is called the urban heat island effect. Plants on roofs actively evaporate water, as well as absorb and reflect sunlight, thereby improving the microclimate in the city. People feel more comfortable and use air conditioning and air purification devices less often in their premises. A study by the National Research Council of Canada (NRC) showed that extensive green roofs reduce the daily demand for electricity used for air conditioning in the summer by more than 75%. In addition to this, plants protect the roof covering from the effects of external factors: sunlight, rain, wind, and sudden temperature changes. This helps to reduce the cost of roof repair and increase its service life.

Green plantings absorb city noise and thus create a more favorable atmosphere both inside and outside the building. They also improve air quality by cleaning it from dust and other pollutants. People who breathe clean air feel much better and are less at risk of developing respiratory, cardiovascular, and other diseases.

The creation of green roofs opens up new employment opportunities: the larger their area, the more specialists are needed to deal with design and maintenance.