What is a green roof? Features and benefits

Part of the architecture is responsible for making more sustainable designs to make energy performance better and the impact on the environment less. One of the techniques used for this is plant cover. The vegetal cover has numerous advantages that we are going to analyze one by one.

In this article we are going to tell you what a green roof is, what its characteristics and importance are.

What is a green roof?

A green roof on a building is a green roof that, together with a roof that contains thermal or photovoltaic solar panels or is protected with a high reflectivity material, increases the energy efficiency of a building as together they save energy consumption. The energy behavior of a building in relation to its surroundings. Also known as green roofs or garden roofs, we can find different types.

Green roofs are a type of roof that is already used in the Nordic countries as insulation. Thanks to its thermal inertia, it controls humidity and regulates the internal temperature. In countries like Iceland, Norway or Canada they are used to insulate, since the vegetation on the roof accumulates heat in winter, while in hot countries like Tanzania they keep the interiors cool despite the external solar radiation.

In the city of Copenhagen, New roof owners have made it mandatory to plant some type of greenery on their roofs. Other countries have regulations that regulate and/or reward the installation of green roofs. It turns out that green roofs help reduce the temperature in cities. It is not about filling all buildings in urban areas with green roofs, but the rational use of technology can reduce the heat island effect caused by high-density buildings, traffic or the use of air conditioning equipment. The heat island effect occurs in cities, where temperatures can rise up to 10 degrees compared to surrounding areas.

Green roof in LEED

LEED tools include, as a sustainable strategy, the installation of vegetative cover for all environmental and economic benefits in the sustainable lot category:

• Reduces stormwater runoff and reduces the risk of flooding since they retain a high percentage of precipitation up to 90%, then a part evaporates and the rest is directed in a delayed manner, and improves its quality by filtering pollutants and heavy metals from rainwater.
• Filters pollutants and carbon dioxide from the airreducing pollution through natural processes.
• It reduces energy consumption as it provides thermal insulation. Due to the thermal inertia that the plant cover can provide as a whole, it can act as a regulator of humidity and internal temperature.
• Increases the life of the roof because the waterproof barrier is protected from solar radiation, heat and cold and storms.
• Reduces heat island effects in urban environments and provide green spaces for planting or recreation depending on the type of vegetation cover.
• Promotes biodiversity since it allows the growth of the species. Developing an urban garden on the roof of an urban environment could be an interesting option, even offering the possibility of growing our own products “at home.

Elements of green roofs

The plant cover consists of the following parts:

• Waterproof jacket. It is placed on roof supports – slabs – for this type of roof they must be resistant to roots. Common practice is to use waterproofing materials such as EPDM, which consists of recycled rubber, or PVC, which is also recyclable. If a flashing panel is used that is not ready to prevent breakage due to the presence of roots, a double layer panel and some type of root protection primer must be applied.
• Thermal isolation. Some green roofs include a layer of insulation.
• drainage layer. Among its functions is to drain the water from the roof, avoiding the stagnation of water and thus preventing the formation of fungi in the roots of the plants. It can consist of a layer of gravel or a layer of HDPE. Polyethylene is a plastic that can be recycled.
• Retention layer. This layer has a concave surface so it can store water from the roof. The drainage layer and the retention layer can be unified into one layer.
• Filter layer. It consists of geotextiles whose function is to prevent the remaining substrate layer from being washed away by water. By avoiding leaching, the substrate retains its properties, favoring plant growth. It is placed on a drainage layer, normally 125 g/m² polypropylene.
• Absorbent layer. The main function of this layer is to retain moisture and gradually release it, especially in dry climates, with little maintenance of the plant cover and rapid evaporation of water. It can be part of the substrate itself or it can be placed under it.
• Substratum. It is the land where plants take root. It must have the right nutrients and acidity for the type of vegetation in which it is grown. The ideal thickness is usually between 4 and 15 cm. The height of the vegetation should not exceed 50 cm.

The substrate is used as a base for the growth of selected vegetation. Additionally, a protective layer can be placed that hinders the growth of plants other than those that need it, and synergistically keeps the substrate moist. This is very practical in dry climates as it reduces the need for watering. For this, padding materials, pine bark, volcanic gravel, etc. can be used. in order to reduce evapotranspiration, especially in dry climates.

Copenhagen does not seem to be an isolated case of this trend or obligation to fill cities with green roofs. The digital newspaper lasprovincias.es published in March 2010 that a revision of the master plan for Valencia, which runs until 2025, can require green roofs on new buildings. A strategy based on environmental criteria to improve the energy efficiency of urban landscapes and buildings.

I hope that with this information you can learn more about what a plant cover is and what its characteristics are.