Green roofs work by creating a roofing surface that allows for vegetation to grow and water to drain through. They absorb rainwater through the build-up of plants, soil, and drainage layer down to the waterproofing membrane and substrate.
Green roofs are usually flat or slightly sloped systems where you can grow low grasses, perennial plants, sedums and even shrubs or trees depending on the kind of green roof. A green roof is an environmentally-friendly option and can be used on a new build or refurbishment project.
Across the various types of green roofs, they have different characteristics but all work in fundamentally the same way. The benefits of a green roof are not limited to the environment - they can also boost well-being and create relaxing green spaces.
Components of a Green Roof
The components of a green roof will vary from project to project, but most will have a similar core buildup.
- Plants: At the top of any green roof there will be a plant layer, the depth of this can vary depending on what type of plants are used.
- Growing medium: Beneath this there will be a substrate which acts as the growing medium for the plant layer on top.
- Filter sheet: Then a filter layer that stops any sediment from being carried out by rainwater.
- Drainage: A Sika drainage board regulates the amount of water kept on the roof to support the plant growth and the excess water going into the drainage system.
- Moisture-retention: Material which helps to retain and draw away moisture off the waterproofing membrane
- Waterproofing: A Sika waterproofing membrane is an integral part of the roof system, playing the vital role of keeping water and moisture away from the building.
- Separation: Sika separation layer for separation (if required) and fire protection between roofing layers.
- Insulation: Sika thermal insulation will enhance the thermal qualities of a green roof system, creating a comfortable environment while reducing heating and cooling costs.
- Vapor control: Sika vapor control that provides an airtight layer with high water vapor resistance.
- Structural deck: Concrete deck with Sika admixtures that enhance the properties of concrete such as durability and strength.
- Roof accessories: Sika scuppers, drains, prefabricated components and more, depending on the project requirements.
Examples of Construction Buildup
For two common types of green roofs, extensive and intensive green roofs, here is how the layers are built. Many of these components can be sourced from Sika – ensuring that the entire system is inter-compatible.
Extensive Green Roof
Intensive Green Roof
Rainwater Retention
During heavy periods of rain, runoff from surfaces such as rooftops can cause issues such as localized flooding and sewer overflow. Green roofs retain up to 75% of the rainwater, thereby slowing the water flow and reducing pressure on storm water infrastructure. Much of the water retained in the roof is used by the green roof plants. Not only does the green roof buildup slow water flow into drainage systems, it also reduces the amount of water. Intensive green roofs tend to absorb more rainfall and runoff than an extensive roof. This is just one of many benefits of vegetated roofs.
Protection Against Water and the Elements
With such water retention characteristics of a green roof, it's essential that they include a robust waterproofing later. The waterproofing layer usually consists of a membrane which is durable and lightweight. Green roofs protect the waterproofing membrane from UV rays, freeze-thaw cycles, and foot traffic - all of which can damage the membrane. Some green roofs in Europe have lasted more than 40 years without being replaced.
Improve Air Quality
Green roofs filter the surrounding air by absorbing carbon dioxide and converting it to oxygen. Airborne pollutants commonplace in most cities will be absorbed into the green roof by rainfall, where they are then filtered out.
Reduce Energy Consumption
Green roofs efficiently insulate the building below. They can reduce energy costs to heat the building during colder seasons while helping keep the building cool in hotter months by lowering cooling costs. Green roofs can also remove heat from the air through the process of evapotranspiration, which reduces the surface temperature of the roof. Energy consumption properties can be enhanced with the inclusion of a thermal insulation layer.
Reduce Heat Island Effect
The heat island effect usually occurs in a metropolitan area with a high concentration of buildings and people, making it hotter than surrounding rural areas. A green roof can reduce this effect by removing heat from the air, reducing the temperature of the roof and the surrounding air.
Insulate Against Sound
Green roofs can be an effective sound insulator. Sound waves are absorbed or deflected off the vegetated layers. The amount of sound and noise insulation depends on the type of green roof used.
Benefits and Types of Green Roofs
By understanding the main vegetated roof types and advantages of choosing a green roof system, you will be well-prepared to implement a green roof into your next project.
Check out our other sources of information for a complete picture of these beautiful, landscaped rooftops.
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Sika has a wealth of roofing experience and has produced more than 1.4 billion square meters of membrane across the world. We have the technical know-how, experience, and expertise to partner with you to ensure you choose the best solution and products for your project.
"When you specify or choose a Sika green roof, you get more than watertight security - you get peace of mind knowing you made the right choice."