2.1 General history of Green wall
Green wall is the common term to refer to all forms of vegetated wall surfaces. Traditional green wall methods are historically known, since the Hanging Gardens of Babylon and the Roman and Greek Empires. In Mediterranean climates, vines were commonly used to cover pergolas, shading the building envelope, or on building walls, cooling the envelope during summer 2. Since the seventeenth and eighteenth centuries, mostly in UK and Central Europe, the use of climbing plants to cover building walls proliferated 3. In the 19th century woody climbers were commonly used as ornamental elements of buildings envelope in European and North American cities 4. First investigations on green facades were based on botanical aspects 1. However, since the 1980s a new idea occurred of green facades as contributors to cities ecological enhancement. The garden city movement from the end of the 19th century marked the integration of greening in urban planning. The German Jugendstil movement (Art Nouveau) from the early 20th century encouraged the integration of the house with the garden. During this period emerged some incentive programs for the installation of green facades. In fact, Berlin is an important example, from 1983 to 1997, where around 245.584 square meters of green facades were installed 1.
3. Module Green Wall is the latest concept compared to the previous two types. It requires more complicated design and planning considerations before a vertical system can come to place. It is also probably the most expensive green walls method.
2.2 Defining Green wall
Green wall also known as vertical greenery is actually introducing plants onto the building façade. Comparing to green roof, green walls can cover more exposed hard surfaces in the built environment where skyscrapers are the predominant building style (Jonathan, 2003).
According to Ken (Ken, 2008), if a skyscraper has a plant ratio of one to seven, and then the façade area is equivalent to almost three times the area. So, if the building is covered two thirds of the façade, this have contributed to doubling extend of vegetation on site. So a skyscraper can become green, thus increasing the organic mass on the site (Wilmers, 1990).
There are three types of Green Walls can be easy found in Malaysia:
The green walls can be divided into three fundamental types according to the species of the plants; types of growing media and construction method.
1. Wall-climbing Green wall is the very common and traditional green walls method. Although it is a time consuming process, climbing plants can cover the walls of building naturally. Sometimes they are grown upwards with the help of a trellis or other supporting systems (Wilmers, 1990).
2. Hanging-down Green Wall is also another popular approach for green walls. It can easily form a complete vertical green belt on a multi-story building through planting at every story compare to the wall-climbing type (Wilmers, 1990).
3. Green facades are based on the application of climbing or hanging plants along the wall. Plants can grow upwards the vertical surface, like traditional examples, or grow downward the vertical surface, in case they are hanged at a certain height. Green facades can be classified as direct or indirect. Direct green facades are the ones in which plants are attached directly to the wall. Indirect green facades include a supporting structure for vegetation. (Wilmers, 1990)