When a building’s roof is covered with a water proofing membrane, root repellent system, drainage system, filter cloth and a growing medium which supports some vegetation, it is called a green roof.
Generally, there are only two types of Green Roofs, they are;
1. Extensive Green Roofs: This is the most basic form of green roofing. It allows for a limited plant species option and can be established on a low-slope (about 40% slopes) and pitched roof. The features of an extensive Green Roof include:
· Light Weight (15 – 50 lbs/sq. ft)
· 3.6 inches soil depth
· The soil requires about 10 – 20% organic matter.
· Usually, vegetation may include meadows flowers, grasses and other plants that require low maintenance, minimum fertilization and irrigation.
2. Intensive Green Roofs: If a roof comes equipped with the proper load bearing capacity, it can be covered with a roof garden. This type of Green Roof will offer a wide variety of plant species including bushes, ponds and even trees. The features of an intensive Green Roof include:
· Heavier Weight, as it can carry up to 150lbs/sq. ft.
· Large Variety of plant species options including terraced surfaces.
· Requires major irrigation, fertilization and maintenance.
HISTORY
The first Intensive Green Roofs conceptually existed as the Hanging Gardens of Babylon built by Nebuchadnezzar II. And then, farmers in Scandinavia were known to have created extensive roofs by placing grass meadows on their roofs and supporting the entire structure with timber beams.
More recently, the concept of Green Roofs was more popular in the UK up until the industrial revolution. Now, Germany boasts of leading the drive for green roofs with 10% of all German roofs covered in vegetation. Other countries like Switzerland are closely following in Germany’s footsteps with regards having their roofs greened.
BENEFITS OF GREEN ROOFS
The advantages of Green Roofs to the environment are quite extensive and very much accepted. These benefits include:
Improved durability and lifespan of the roof.
Substantial reduction in urban heat island effect.
Reduced surface water runoff.
Decline in the heating and cooling demands for the building as the seasons change.
DISADVANTAGES OF GREEN ROOFS
The UK and several other countries are discouraged from the full adaptation of Green roofs due to the following reasons:
Increased structural load for the entire building.
Installation requires higher capital than for their traditional counterparts.
There are higher maintenance requirements, even for extensive Green roofs
Inadequate or complete lack of specialized contractors for technical installation.
Globally, there is little or poor understanding of the benefits of Green Roof technologies especially in tackling environmental problems, and where there is an understanding; implementation can be described as immature at best. In Europe, where the concepts of Green Roofs have been embraced there is substantial evidence of government support by legislation and finances. And so, despite the factors hindering the adaptation of the Green Roof Technologies, countries like Germany, France, Austria and Switzerland have created a multi-million dollar market for Green Roof products and services. In Africa, the concept of green roofs is foreign at best, however, similar techniques have been used over the years to control temperatures within homes.