Green roof is a cool way to make buildings more eco-friendly and beautiful at the same time.
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What Is Green Roof?
A green roof, also known as a living roof, is a special kind of roof that has plants and soil growing on it. It’s like having a mini garden on top of a building! The roof is made waterproof to protect the building, and then a layer of soil is added. Plants are planted in this soil, creating a beautiful green space.
Green roofs have many benefits. They can soak up rainwater, which helps prevent flooding. They also act as insulation, keeping the building cool in summer and warm in winter. The plants on the roof create a home for birds, butterflies, and other wildlife. Plus, they make the area around the roof look nicer and more pleasant. Green roofs even help cool down cities, where it can get very hot, by reducing the “heat island” effect.
There are different types of green roofs. Some are thicker and can support a wide variety of plants, but they need more maintenance. Others are shallower and require less upkeep. Green roofs can be added to existing buildings or included in the design of new ones. They can be found on small buildings like garages or big ones like offices and even city halls.
Sometimes the term “green roof” is also used to describe roofs that use other environmentally friendly technologies. For example, there are roofs that have solar panels to collect energy from the sun or special roofs that help keep buildings cool. These roofs are also considered “green” because they are good for the environment.
Types Of Green Roofs
- Extensive Green Roofs: Extensive green roofs are designed to be low-maintenance and self-sustaining. They typically consist of a thin layer of soil or specially formulated compost, which supports lightweight vegetation such as Sedum species and mosses. With vegetation weighing around 50–120 kg/m2 (10–25 pounds per square foot), extensive green roofs require minimal maintenance, often limited to a yearly weeding or the application of slow-release fertilizers.
- Intensive Green Roofs: Intensive green roofs are more labor-intensive and offer greater versatility in terms of plant selection and design. They require a deeper planting medium, accommodating a wide range of plant varieties, including kitchen herbs, shrubs, and small trees. With a higher vegetation weight of 390–730 kg/m2 (80–150 pounds per square foot), intensive roofs create a park-like environment with easy accessibility. However, they necessitate irrigation, feeding, and regular maintenance to sustain optimal plant growth.
- Comprehensive Green Roofs: Comprehensive green roofs blend the advantages of both extensive and intensive green roofs. These systems support plant varieties typically associated with intensive green roofs, but at the depth and weight characteristics of an extensive green roof. By combining the desirable features of each type, comprehensive green roofs offer a balance between plant diversity and reduced maintenance requirements.
- Pitched Green Roofs: Pitched green roofs are commonly found in Scandinavian architecture, featuring a sloping roof structure. Due to the roof’s angle, the risk of water penetration is reduced, necessitating fewer layers of waterproofing and drainage. These roofs often have a simpler design compared to flat green roofs.
- Flat Green Roofs: Flat green roofs are horizontally oriented and offer greater flexibility in terms of design and vegetation choices. They require a comprehensive waterproofing membrane to protect the underlying structure from water damage. Flat green roofs can be either extensive or intensive, depending on the depth of the planting medium and the desired maintenance level.
Advantages Of Green Roofs
- Cleaner Air:
- Green roofs act like green walls, filtering pollutants and carbon dioxide from the air.
- They help reduce asthma and other diseases caused by poor air quality.
- Carbon Storage:
- Green roofs absorb and store carbon, which is good for the environment.
- Plants on the roofs naturally take in carbon and keep it in their tissues and the soil.
- Energy Savings:
- Green roofs insulate buildings, keeping them warmer in winter and cooler in summer.
- This helps save energy by reducing the need for heating and cooling.
- Noise Reduction:
- The soil on green roofs blocks low-frequency sounds, while plants block higher frequencies.
- They act as natural sound barriers, making buildings quieter.
- More Space for Farming:
- Green roofs create extra space for urban farming and gardening.
- People can grow their own food, which is good for the environment and local communities.
- Better Water Management:
- Green roofs retain rainwater, preventing excessive runoff and reducing strain on drainage systems.
- They also filter pollutants from rainwater, keeping our water cleaner.
Disadvantages Of Green Roof
- High Initial Cost: Installing a green roof can cost twice as much as a regular roof, making it an expensive investment at the beginning.
- Maintenance Costs: Different types of green roofs may require higher ongoing maintenance expenses, although some have minimal or no recurring costs.
- Waterproofing Challenges: Green roofs can put extra pressure on the building’s waterproofing system. Water retention on the roof and roots potentially penetrating the waterproof membrane can undermine its effectiveness.
- Pest Infiltration: Wildlife attracted to green roofs, including pests like insects, can easily enter residential buildings through open windows, causing problems.
- Structural Strain: The additional weight of soil and water retained by green roofs can heavily strain the building’s support structure. It’s challenging for buildings to accommodate such added weight, making it unlikely for intensive green roofs to be widely adopted without costly reinforcement.
- Limited Applicability: Retrofitting certain buildings with green roofs may not be feasible due to the excessive weight of the soil and vegetation exceeding the building’s permitted load capacity, especially in areas prone to earthquakes.
- Risk of Roof Collapse: Green roofs have been known to cause roof collapses. For example, in 2016, the weight of a green roof led to the collapse of a large sports hall roof in Hong Kong, resulting in the removal of other green roofs in the region.
- Increased Maintenance: Green roofs require more maintenance and energy compared to regular roofs. This includes tasks like clearing debris, controlling weeds, trimming, monitoring moisture levels, and fertilizing.
- Watering Requirements: In regions with limited rainfall, green roofs need to be watered regularly, leading to higher energy consumption for maintenance.
- Embodied Energy: The manufacturing process of green roof components and their associated CO2 emissions result in higher embodied energy compared to conventional roofs.
- Runoff Quality Impact: Both sod roofs and roofs made with Lightweight Aggregates (LWA) have been found to negatively affect the quality of the water runoff they produce.