If the top of the roof is covered with a layer of vegetation planted over a waterproofing system, then it is said to be a green roof.
Both flat or slopy roofs can be easily extended into a green roof.
This roof is also known as an eco-roof or vegetative roof.
It should have a minimum of 5 layers ( i.e. waterproof membrane layer, root barrier layer, drainage layer, filter layer, and vegetation layer ).
The waterproof membrane layer plays a vital role in eliminating roof water leakage. Similarly, a root barrier prevents roof damage from roots, a drainage layer is essential for proper drainage of water during rain & irrigation, a filter layer is essential for preventing soil erosion and a vegetation layer is vital for the survival and growth of plants.
The vegetative layer acts as insulative to sound and heat. So, the Insulating layer in the green roof can be neglected.
The green roof may consist of more than 5 layers. Extra layers that can be provided are the insulating layer, vapor control layer, protection layer, etc. These layers are added based on the plant selection.
Selection of plants for vegetation layer is done based on the types of green roof.
1. Myths About Green Roof :
a. It is an experimental part of the green trend:
Most people think green roof construction is a new and experimental part of the green trend. But this is untrue.
This roof has been around for centuries.
b. Green roof can cause structural problems :
The green roof only imposes dead loads on the structural parts which are transferred to the earth. So a green roof doesn’t lead to any structural problems.
c. It is costly and difficult to irrigate green roof :
We can easily irrigate green roof by ourself.
If the climate is hot, then drought-tolerant plants are selected and for cold climates, normal plants can be utilized.
Irrigation is generally required at the early stage of plant development. After the complete development; irrigation can be cut down to once a week or once a month depending upon the local climate. In some climates; no irrigation may be required.
d. They may cause roof leakage :
The main reason behind the roof leakage is the use of a low-quality waterproofing membrane. The selection of quality materials eliminates the chance of roof leakage.
e. It is expensive and complicated to construct a green roof :
The construction cost of a green roof is low ( i.e. $10 to $30 per sq. ft.) as well as it is not complicated to construct them.
2. Construction of Green Roof :
It is a ready-made green roof.
a. The small rectangular or square pieces of a green roof are produced at factories and transported to the site.
b. Then the pieces are arranged and fixed on the roof.
Its construction cost is cheaper and less time-consuming than that of an onsite constructed green roof. It is suitable for an extensive green roof rather than an intensive one.
b. Onsite Constructed
When the green roof is constructed at the site then it is known as an onsite constructed green roof.
Construction steps involved are:
1. Preparation of the base :
For the case of old or already constructed buildings and concrete buildings; existed roof is taken as a base.
But for wooden buildings under construction; the base of the roof is prepared by installing aluminum sheets or ply sheets on the frame prepared.
For a better result; ply sheets are provided at the bottom and aluminum sheets are provided at the top.
2. Providing waterproofing membrane layer
This layer is prepared in the following steps:
a. At first, bitumen sheets are laid over the base such that sheets properly bind with the base layer and also protect the base from leakage.
b. Above bitumen sheets; a plastic layer is provided. The joints between plastics are made watertight with the help of aluminum tape.
3. Providing Insulation layer
For better insulation from heat and sound, this layer is provided above the waterproofing membrane layer.
The vegetation layer acts as insulative. So this layer can be neglected if required.
4. Providing root barrier
The root barrier layer is provided for the protection of the roof from roots.
5. Provision of the protection layer
A protection layer is provided for ensuring extra protection of the system. This layer is generally provided for the intensive green roof.
6. Provision of the drainage layer
The aim behind the provision of a drainage layer is the safe disposal of excess water during rain or irrigation.
7. Providing filter layer
The filter layer is provided to separate the soil and water. Geotextiles are commonly used for the filter layers.
Simply, the filter layer prevents the erosion of soil particles.
8. Providing vegetation layer
A layer of soil having sufficient thickness ( ranging from 3 inches to 12 inches) for plant growth is prepared and then plantation is done.
3. Types of Green Roof :
a. Extensive Green Roof
The thickness of the vegetation layer in this roof type varies between 3” to 8”. It is suitable for small plants like desert grasses, succulent plants, etc.
Due to its lightweight; it is suitable for light as well as heavy structures.
The construction and maintenance cost of this green roof is very low as compared to the intensive one.
This roof seems to be unattractive during the winter season.
It is suitable for flat roofs as well as for sloppy roofs ( up to 45°).
b. Intensive Green Roof:
The thickness of the vegetation layer in this roof varies between 8” to 12”.
Plantation of diverse plants and trees can be done.
Plants with invasive root systems should be avoided.
This roof has a huge weight and is suitable for heavy structures.
The cost of construction and maintenance is high as well as an irrigation system is required in this type.
It is more complex to construct as compared to an extensive one.
It looks very attractive and even can be utilized as a park, playground, and vegetable garden.
c. Semi-Intensive Green Roof
It is a hybrid roof. It has the features of both extensive as well as an intensive green roof.
4. Difference Between Extensive and Intensive Green Roof :
|S.N.||Extensive Green Roof||Intensive Green Roof|
|1.||The thickness of the vegetation layer varies between 3” to 6”.||The thickness of the vegetation layer varies between 8” to 12”.|
|2.||Suitable for small desert grasses and succulent plants.||Suitable for most plants (without invasive root systems).|
|3.||It is cheaper to construct and maintain.||It is expensive to construct and maintain.|
|4.||After the proper development of plants; irrigation may not be required.||Irrigation is required continuously except in rainy seasons.|
|5.||It is lightweight.||It is heavy in weight.|
|6.||It is suitable for flat as well as slopy roofs.||It is only suitable for flat roofs.|
|7.||It is less complex to construct.||It is more complex to construct.|
|8.||It can’t be utilized as a park, playground, or vegetable garden.||It can be utilized as a park, playground, or vegetable garden.|
|9.||It is less attractive ( mainly in winter).||It is more attractive throughout the year.|
5. Advantages :
a. It improves the aesthetic beauty of the building.
b. It provides a rainwater buffer.
c. It purifies the air.
d. It reduces the ambient temperature.
e. It improves the efficiency of solar panels.
f. It also provides insulation to sound by reducing ambient noises inside and outside.
g. It extends the life span of the roof up to 60 years or even longer which is double or triple the lifespan of a normal roof.
h. It supports biodiversity.
i. It acts as a fire-resistant layer.
j. They reduce the electromagnetic radiation penetration up to 99.4 %.
k. It helps in improving health and well-being.
l. For the long term, it saves a lot of time and money.
6. Disadvantages :
1. Requires irrigation and maintenance.
2. Imposes dead loads on the structure.
3. Leakage may occur if quality materials are not used.
7. Cost of Constructing :
The cost for the green roof construction may vary between 10 $ to 30 $ based on types of green roof selected, plants selected, quality of materials used, etc.
a. Do you suggest having a green roof?
Yes, of course. We strongly suggest you for having this roof.
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Civil Engineer & CEO of Naba Buddha Group