Types of Green Roofs
Extensive landscaped roofs are an ecological alternative to conventional surface protection or ballast layers such as gravel and pavers. They are lightweight and have a shallow build-up height. Suitable plants include various Sedum species, herbs and some grasses. After establishment of the vegetation, the maintenance is limited to one or two inspections a year.
If designed specifically to increase the biodiversity and attract a particular fauna and flora, they are called “Biodiverse Green Roofs”. Biodiverse green roofs reproduce natural habitats and attract flora and fauna into the area, e.g. by providing food, nesting opportunities or resting places for creatures, such as spiders, beetles, butterflies, birds, etc.
- Adapted plant communities
- Minimal maintenance required
- Supply of water and nutrients mostly by natural processes
- Shallow build-up height
- Weight approx. 50–150 kg/m²
Semi-intensive green roofs incorporate the benefits an intensive green roof while not having to redesign an existing structure to support a heavy system. The concept is to incorporate intensive aspects where the structure can support them as well as having areas of extensive green roof where the structure would need to be strengthened.
Semi-intensive green roofs can have many of the benefits of an intensive design without the huge expense of rebuilding an existing roof structure. These designs also provide an opportunity to be very creative and smart about the design of your green roof system.
Intensive green roofs are the equivalent of a garden on your roof. They are accessible and very broad in their function. Intensive green roofs give the most benefits in all aspects compared to the other types. These do require significant structural design and are best suited to being designed into a new building.
Intensive green roofs can support a much larger range of plantings such as small trees and shrubs therefore helping the most to increase biodiversity, reduce energy costs for cooling, harness and filter more water, filter more air and provide more flexibility for interaction with the green roof.
The heights of these roofs are much larger than other types and typically weigh around or above 150 kg/m²
Green Roofs and Solar Energy
Solar panels work most efficiently when they are cool, however, they need to be in direct sunlight. Traditional roof membranes absorb and re radiate a lot of the suns energy which heats up the solar panels, adding to the heat already present from the solar panels being in direct sunlight. Pairing a green roof with your solar panels helps to keep them cool and therein helps them work more efficiently and perform better.
Green Roof Structure
A typical Green roof will consist of a structural layer, waterproofing, root repellent, filter, drainage, growing medium, irrigation, plants and other garden features. It will also have well designed flashings, and drainage systems. There are also optional layers of water retention material, membrane protection, insulation, water holding tank and an erosion protection layer. Optional features include walkways, lighting, water features, garden borders and railings. The essential component functions are as follows:
This is the roof which the green structure will sit on. The building material, concrete, steel or wood, influences the subsequent structure design and the attachment method. Concrete is the best suited structure for green roofs. The main consideration for the structural layer is the weight of the green roof layers.
The waterproofing membrane is an essential layer of material which, along with other features such as drainage and flashings, prevents any water from passing through to the structure underneath. There are various attachment and material choices of waterproofing membranes for different green roof designs. Sometimes a membrane protection layer is introduced to protect this vital layer from damage during roof construction.
Root Repellent Membrane
Repelling or barring of roots can be chemical or structural and is essential so the waterproofing membrane is not punctured and rendered useless by plant roots.
Drainage consists of a drainage layer which removes enough water from the roof in order to not compromise the waterproofing membrane. It does this in conjunction with other layers as well as drains, pipes, and possibly water retention tanks and water features. The drainage layer could consist of porous mats, boards, foams, capillaries or aggregates.
The filter membrane allows any water through to the drainage layer while protecting it from any blockages by small particles of soil from the growing medium above. This is a lightweight, rot-proof, synthetic material.
The growing medium can be organic (compost or sawdust) or inorganic (aggregates or minerals) or a mixture of the two. It drains water from the roof and supplies nutrients to the plants. The success of a growing medium needs to be considered for the long term and is highly influenced by the vegetation varieties used and the climate the roof is exposed to. When choosing a growing medium slope, density, irrigation method, availability must also be considered.
Irrigation systems regulate and moderate water application to the growing medium to ensure plants grow and thrive long term. Irrigation can be automated, natural or manual depending on roof size, accessibility and type.
These green roof systems are built up in layers of the various materials required for a green roof. These are necessary for intensive green roofs, large roofs and unique designs. Loose-laid roofs give maximum flexibility for your green roof content and from.
Modular green roofs combine two or multiple components of the system in one product. Often these are modular and can be retrofit. They may not always contain all the components necessary to install and green roof however. These systems are most suited to extensive or semi-intensive roofs and because they are modular can be grown offsite and installed quickly with significant growth, similar to a modular green wall system. These systems can usually allow quick access to the underlying roof for and maintenance needs. Modular green roofs are also suited to more temporary green roof solutions.
Why is soil so important?
Air quality is a major concern for city dwellers. Smog and pollution leads to asthma and respiratory problems (Timonen and Pekkanen, 1997), especially the presence of nitrogen oxides, carbon monoxides and sulphur monoxides which are emitted from cars and industrial sites. Poor air quality in urban areas has been estimated at killing 800,000 people every year around the world (Kenworthy, 2002).
Soil in a living architecture structure traps particulates and captures toxic gases. It also regulates indoor temperatures and lowers summer highs. This reduces energy usage and the associated pollution from running heating, ventilation and air conditioning systems.
Aside from the thermal mass provided, vital soil functions are the reason why soil gives us so much value and improves our environment. Those functions can be classified as follows:
Soil stores, moderates the release of, and cycles nutrients and other elements. During this, similar to a water cycle, nutrients are transformed into plant absorbable forms, retained, or lost through air or water.
Soil moderates flow and storage of water, including solutes in the water such as nitrogen, phosphorus, pesticides, and other compounds. When healthy, soil partitions water for ground absorption and plant and animal use.
Soil provides a diverse chemical and physical environment to help a variety of plants, animals and organisms thrive together. This environment is automatic and regenerative as opposed to a synthetic growing membrane which needs to be designed for specific growing environments.
Soil functions as a filter for air, water and other resources. Toxic chemicals can be made unavailable to plants and nutrient levels regulated.
Soil provides a medium for plant roots, avoiding erosion while maintaining its porous structure for water retention and circulation. Soil can also support other man-made structures and protect building surfaces.