Green roofs: much more than just a trend

An eco-friendly solution to improve the environmental footprint of buildings

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By Alex

green roofs

Green roofs have an excellent insulating effect, helping to reduce the energy consumption of a building in cold seasons and keeping it cooler in hot ones. But the benefits don’t stop there: everything you need to know on the subject and… some truly remarkable examples!

The trend of green roofs is spreading worldwide: in some countries, the UN points to rooftop urban gardens as a concrete crisis-fighting measure and aid to the subsistence of the population in certain countries. However, they also provide a pleasing aesthetic and offer several other tangible advantages.

Integrating urban buildings with green roofs is not only an operation that impacts air quality and landscape but also a way to transform constructions by giving them greater energy efficiency.

What are green roofs, exactly?

Green roofs, also known as living roofs or eco-roofs, are roofs of buildings that are partially or completely covered with vegetation and a growing medium over a waterproofing membrane. Instead of the traditional roofing materials like asphalt, shingles, or metal, green roofs incorporate plants and soil, creating a living, functional space on top of the structure.

Types of Green Roofs

There are two main types of green roofs: intensive and extensive.

Intensive Green Roofs

  • Description: Intensive green roofs are characterized by a thicker growing medium, allowing for a more diverse selection of plants, including shrubs, trees, and even small gardens. They are like rooftop parks or gardens.
  • Features: Intensive green roofs require more maintenance and structural support due to the added weight. They offer recreational space and may include walkways, seating areas, and even water features.

Extensive Green Roofs

  • Description: Extensive green roofs have a thinner growing medium, which limits the types of plants that can thrive. Typically, they feature low-growing vegetation such as sedums, grasses, and other hardy plants.
  • Features: Extensive green roofs are lighter, require less maintenance, and are more common on residential and commercial buildings. While they may not provide recreational space like intensive green roofs, they still offer environmental benefits.

Key Components of Green Roofs

  1. Waterproofing Layer: This layer ensures that water does not penetrate the building structure.
  2. Root Barrier: Prevents plant roots from damaging the waterproofing layer.
  3. Drainage Layer: Allows excess water to flow away, preventing waterlogging.
  4. Growing Medium/Soil: Provides a substrate for plants to grow and support their root systems.
  5. Plants: The type of plants depends on the green roof type (intensive or extensive).
  6. Protection Fabric: Protects the waterproofing layer from mechanical damage during installation and maintenance.
  7. Irrigation System: Some green roofs may include irrigation to ensure plant health, especially in arid climates.

Let’s now explore the advantages of a green roof in more detail.

Green roofs: key benefits

  1. First and foremost, green roofs help decrease water infiltrations. In certain cases, especially in summer, water infiltrations are almost completely eliminated. A well-designed green roof absorbs rain up to 90% of the usual runoff, thereby reducing the water load on sewage systems.
  2. The second significant advantage of having a green roof is energy savings. A green roof serves to better insulate the building and protect it from the summer sun. In a building with an extensive green roof, this savings can reach several hundred euros. This function as a thermal insulator and regulator has been known since ancient times. It is true that a green roof involves initial costs, but these are quickly amortized.
  3. This brings us to the third significant advantage associated with green roofs, which contribute to the absorption of CO2 in the atmosphere: if present in large quantities, they could significantly contribute to improving urban air quality.
  4. Green roofs act as a natural barrier against noise pollution. The green roof can absorb external noises, reducing sound reflection by 3 to 8 decibels, depending on the components used.
  5. A green roof can protect the roofing materials from temperature fluctuations, ensuring perfect ventilation of the layers.
  6. Green roofs are a biodiversity aid: green roofs increase urban green spaces and, above all, serve as a hospitable habitat for birds and various animal species.
  7. A green roof supports photovoltaics, doubling energy benefits and synergistically combining the electricity produced to power the irrigation system.
  8. Fighting smog: as plants produce oxygen, especially in cities, they capture CO2 and some pollutants, helping us naturally combat air pollution.
  9. Green roofs contribute to combating the heat island effect: in cities, temperatures are always higher than in the countryside; well, here is help to limit the phenomenon.
  10. Green roofs also offer an additional advantage to consider: the possibility of having additional cultivation surfaces for urban agriculture, for the creation of suspended gardens, or simply to enjoy elevated gardens where one can reconnect with nature even in the city center.

So, the advantages of a green roof, like those of green walls, are numerous: in particular, they mean absorbing highly polluting and dangerous agents such as fine particles; they allow greater regulation of internal temperatures in buildings; the roof lasts longer as it is protected from the weather; there is greater energy savings, especially in summer, thanks to the cooling effect provided by the greenery.

And the costs of a green roof?

Understanding the financial implications is crucial for encouraging widespread adoption and addressing concerns related to affordability.

Regarding the costs of a green roof, we must distinguish between those of implementation and maintenance. Implementation costs can vary significantly, depending on the complexity of the work and the materials used, but a range of 50 / 60 dollars per square meter can be assumed. However, let’s not forget that many countries have tax breaks for energy redevelopment interventions (including green roofs) for buildings.

As for maintenance, there are no higher costs than those of ordinary garden care.

Of course, before embarking on this project without incurring subsequent costs and inconveniences, all authorization aspects (local regulations, especially in areas with strong landscape constraints and condominium regulations) and technical aspects, particularly the resistance of the roof where this healthy splash of green is intended, must be verified.

Unlike rooftop gardens, green roofs are relatively light and can even be installed on sloping and undulating surfaces, not necessarily flat. Their weight does not exceed 120 kilograms when wet, allowing for truly original implementations, as we will see later.

Green Roofs: Some Notable Examples

Let’s see some remarkable examples (or even so original as to appear bizarre at first glance) and around the world.

The Library of Birmingham (United Kingdom)

This building boasts a distinctive green roof with terraced gardens. The roof design incorporates a variety of plants and green spaces, offering visitors a visually appealing and eco-friendly environment.

green roofs
Snapshot of thegreen roof of the library of Birmingham.

The School of Art, Design and Media at Nanyang Technological University (Singapore)

This building is known for its undulating green roof that seamlessly blends with the surrounding landscape.

The roof is covered with vegetation and serves as an extension of the campus, providing students with a unique and tranquil outdoor space.

The California Academy of Sciences (USA – San Francisco)

The living roof of one of the most famous eco-friendly museums in the world is another notable example. It features native California plant species arranged in a wave-like pattern. The roof provides insulation, captures rainwater, and supports biodiversity, contributing to the academy’s commitment to sustainability.

green roofs - The California Academy of Sciences
The unique green roof of the California Academy of Sciences

The Siam Green Sky (Thailand – Bangkok)

The Siam Green Sky is a green roof project atop the Siam Paragon Mall in Bangkok. It features a lush green space with trees, plants, and walking paths. The green roof serves as a recreational area for visitors and helps reduce the heat island effect in the bustling city.

The High Line (USA – New York City)

The High Line is an elevated park built on a disused railway track on Manhattan’s West Side. While not a traditional green roof, it incorporates greenery and landscaping, creating a unique linear park with walking paths, seating areas, and a diverse selection of plants. It has become a popular public space in the heart of New York City.

green roofs
The High Line is a unique elevated park built on a historic freight rail line on Manhattan’s West Side in New York City.

Vancouver Convention Centre (Canada)

The Vancouver Convention Centre features one of the largest green roofs in North America. It covers six acres and includes a variety of native plant species.

The green roof provides insulation, reduces stormwater runoff, and offers stunning views of the city and waterfront.

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