A green roof or vegetated roof is a building’s roof that is covered partially or completely with plants.
A green roof is a system and green technology that consists of plants layer, growing medium (soil), root barrier layer, drainage layer, filter fabric, waterproofing membrane and sometimes irrigation system.
Roofs that contain potted plants do not fall under the green roof term.
People discover green roofs since ancient times. As hanging gardens of Babylon are a mix of living walls and green roofs.
In modern history, Europe in general and especially Germany pioneered the rediscovery of living roofs in the 1960s. Since then green roofs started to spread through many European countries.
lately, the public awareness of green roof system benefits started to arise in North America, which led to more adoption.
Many countries and states regulate incentives for property owners who installed the green roof properly in their buildings. Due to the fact that green roofs have many environmental benefits.
Green roof components
Green roof system generally contains six components:
1. The planted layer
It is the upper layer ( green roof plants ).
2. The growing media ( Growth substrate)
It is the green roof soil. The depth and intensity of this layer determine the type of plants that can be planted.
3. The filter layer
Works as a filter that prevents soil particles from blocking the drainage layer.
4. Drainage layer
The drainage layer draining the excess water from the growing media. It determines the humidity level of the soil and it affects the roof capacity to store and retain water. Therefore it improves the thermal properties of the roof.
5. Protection layer
The protection layer functions as protection to the roofs waterproof membrane from damages following green roof installation. And also double the protection from the plant’s roots roof penetration.
6. Roots barrier
The root barrier layer protects the roof structure from plant roots penetration.
Green roof types
Living roofs can be classified according to maintenance requirements, plants types, wights, costs and usage into three different types:
Extensive green roof
An extensive roof has thinner lightweight growing media that ranges between 6cm to 20cm in thickness.
It requires low maintenance. Due to the fact it only accommodates plants that require little to no watering like moss, sedum, herbs, and grasses.
It weighs between 60 to 150kg/ m². Therefore it is suitable for roofs that cannot take much weight.
Extensive green roofs are mainly used for ecological and roof protection purposes.
Intensive green roof
Intensive green roofs have thicker growing media typically between 20cm to 100cm. Which allows it to host more plants varieties ( perennials, shrubs, and trees).
The downside of intensive roofs that it is heavier which requires special building structure. It wight between 180 to 500kg/ m². It is the most expensive type of green roof.
The diversity of plant types and sizes in the intensive green roof makes it useful as an accessible roof garden.
Intensive green roofs encourage biodiversity more than the extensive ones. Due to its deeper growing medium which stores more water and hosts more insects.
The maintenance and keep up in intensive roof is high.
Semi-intensive green roof
As its names indicate it is a mix between the two types. It wights about 120 to 200kg/ m² which is heavier than extensive roofs but lighter than the intensive ones.
its advantage is that it allows for more design possibilities and it can accommodate shrubs beside grass and herbs.
It typically has a moderate cost when compared to extensive and intensive roofs. Semi-intensive roofs require regular irrigation.
Green roofs benefits
Green roofs have environmental, economic and other benefits.
living roof environmental benefits
Human being colonized earth. We do things in order to gain immediate or short term benefits without taking into consideration the long term consequences. We see this pattern in our behavior.
Unfortunately, the modern civilized human being did and still doing things that future generations will pay a high price for his wrongdoings.
As the human race population increases the need for shelter, buildings and cities increases.
unfortunately, societies shift to urbanization to meet the growing population number without considering how it is affecting the environment. Which we are part of it and our survival depends on it.
Unless Elon Musk and other space pioneers who try to find us a new planet to colonized find it. So better to get down to earth and find ways to sustain it.
Green roofs are one of those methods that can help in this matter. Keep reading to know-how.
Reducing urban heat island
Urban heat island is the phenomenon that urban locations are hotter than the rural or less developed ones.
The main cause of this situation is urban areas have more man-made solid surfaces.
By installing a green roof you did the world favor. Since your green roof will absorb heat and moderate the temperature level. Instead of transferring heat as it is without any processing as other ugly black conventional roofs do.
The green roof adoption can reduce the building’s energy consumption on cooling in summer and heating in winter.
The process of evapotranspiration creates a cooling effect on rooftops in summer which leads to less energy consumption in cooling.
also, the green roof membrane works as a heat barrier between solar radiation and building surface. Therefore the heat flow to the building is dramatically lower than conventional roofs.
The plant’s shades also add to the heat flow resistance to the building. Although this effect depends on the green roof plant types.
plants such as sedum spurium and sedum kamtschaticum are useful when it came to heating reduction throughout the year.
another factor is the depths of the growing medium. The deeper the growing medium the less heat flow to the building.
The heat transfer into or from the roof on buildings with a green roof can be reduced to 72% compared to black roofs. Therefore the energy need for cooling in summer is less with a green roof.
Also, the green roof membrane retains more heat in winter. According to study winter heat loss for green roofs is 34% lower than for conventional roofs.
the study showed that the energy-saving during winter is 13% to 33%. Although the energy consumption saving in summer is greater than in winter.
Another factor that contributes to the energy-saving is that many buildings have cooling and/or heating equipment located in the rooftop.
The shifts in the roof temperature due to the green roof effect make the roof air warmer on the equipment intake point in winter, and cooler in summer.
which causes the cooling and heating equipment to consume less energy to cool or heat the building.
Biodiversity is important to the ecosystem, urban areas generally are places that are discouraging biodiversity. A green roof can be a solution to this problem.
a well established and designed green roof can encourage biodiversity.
Designers can design a green roof that is able to habituate different types of plants, insects, and animals. By varying the depth of the soil. Some plants have a deeper root system and need a deeper growing medium that able to accommodate the roots and to store more water.
Other plants that are drought tolerant with shallow root systems can be grown successfully in a thinner growing medium.
Generally speaking, the depth of the soil allows more biodiversity in terms of plants, insects, and birds.
The green roof absorbs stormwater
In rural and natural landscapes the rainwater first falls in trees or plants leaves. Which absorbs a portion of this water to use again in the evapotranspiration process. The remaining portion of the rainwater will be stored in the soil. This is how nature works!
In cities normally rainwater falls directly on solid surfaces without any absorption with added pollutants that already in those surfaces. Then stormwater goes directly to sewer systems which increases river banks’ floods and soil erosion.
But when you add to your building a green roof you are contributing to solving this problem.
The plants in your rooftop will absorb a portion of the stormwater. And the soil layer will retain portion and filter the excessive portion. Which will be drained through the drainage layer either to a sewer system or another designed system that can use it instead of wasting it.
Improving air quality
Since long time plants have been used to reduce carbon emissions and purify the air in cities. Green roofs expand the green area in cities which increases the air quality.
Green roof economical benefits
According to a study the life span of a green rooftop is expected to be 40 years. While the conventional black roof lasts for 17 years.
Therefore installing a green roof has economical benefits due to the longevity of the building’s roof life span.
Properly installed green roof has more than doubled the life span of the conventional one. This because the growing medium and the plants of the green roof protect the roof membrane from UV radiation and temperature fluctuations. Which damages the roof membrane through the process of expansion and shrinking.
Adds value to the building
Market research results showed that buildings with green roofs have higher value and price when compared to similar buildings that have a conventional rooftop.
Green roof layers make it harder to fire to expand through the rooftop because of the humidity of the soil.
Enhancing human well being and quality of life
Studies showed that living or working on areas that are green enhance psychological well being. Increase interaction between family members and coworkers and decrease vandalism.
Also, patients who are exposed to green areas showed a faster recovery period than patients who are in conventional hospitals environment.
Green roof layers work as barriers to outside noise to get into the building. Although the buildings that are located in areas near highways or air traffic receiving the greatest benefits of noise reduction.
Green roofs for urban agriculture
For green roofs to be used as urban farms, the soil or planting media should be more than 6 inches. Although herbs like kale, spinach, and lettuce crops can be planted in the extensive roof.
For more food production diversity green roofs should be either intensive or semi-intensive ones.
Using roofs for urban garden and food production benefits the environment by decreasing the carbon emissions associated with food distribution. It also helps to deliver fresher vegetables and crops to cities.
Canadian study estimated that using all the rooftops in Toronto to produce crops could create a return of CAN$1.7 billion.
it is very useful to use rooftops for urban agriculture,
Although there are challenges that come with it. Since farming requires labor the design of the green roof should allow the roof accessibility.
Another thing to be carefully considered is that many crops require deep soil. Which means more weight to be handled by the building structure.
Designers should assess the building load-bearing capability and design the urban garden accordingly. Or modify the building structure which will increase the farm overall cost significantly.
Further to add is that roof urban garden increases the roof maintenance cost.
Green roofs design and construction challenges and their solutions
The main design, installation and maintenance challenges of green roofs are:
The ability of the building to support the green roof
Designers should make sure that the load-bearing of the building can handle the weight of the green roof.
Quality installation and leak prevention
Engineers should make sure that the material used in the root barrier layer strong enough to prevent the roof penetration.
Also, they should ensure there is no water leak from the green roof.
There are three types of green roofs as I mentioned before. Each one of the three types requires a different level of maintenance and irrigation.
Building owners should know the amount of time, effort and money they are willing to spend on their green roof. And choosing the type accordingly.
Plant loss due to environmental conditions
Each green roof type has the ability to accommodate certain plants. For example, an extensive green roof accommodates only plants that are drought tolerant with shallow root systems. Since the depth of its soil 6 inches or less.
Therefore plants that have deeper root systems should not be planted in an extensive green roof. While intensive green roofs have deep growing media that can support the growth of little trees.
What is important is designers or owners should select plants according to the depth of the soil. And it’s capacity to store water.
The intensity of sunlight and winds in the roof determine the type of plants that can be planted.
Happy green roofing!
The website does not hold any responsibility upon any action taken by the reader after reading this article. If you are willing to install intensive or semi-intensive green roofs please consult professionals in load-bearing to assess your site.