Green Walls in High Rise Buildings -Types, Features and Benefits

Green walls have been used for centuries in building construction as a means for providing shades to the building walls and the atrium. These walls also help to shield the buildings from wind.

Green walls also facilitate the growth of the agricultural plants. This is a kind of vertical vegetation that is implemented in the building structures. The figure-1 shows the Hanging Gardens of Babylon, which is considered as the seven wonders of the world. This is an original concept of a green wall in the period between 600 to 800 B.C.

Fig.1: Hanging Gardens of Babylon- A simulated Picture

In many northern countries, the vegetation was integrated into the building tradition. Here a turf or a top layer of soil that consists of grass and roots called as sod, are used as the roof material or as the facade material.

The figure-2 shows the Vikings Building that is covered with turf. This provides a greater insulation against severe weather conditions due to cold. The material sod was used in the northern countries that provide good thermal insulation but was not a good structural material. The sod was highly susceptible to water penetration due to rain and snow, which will result in its damage.

Fig.2: Icelandic Turf Houses- Viking Buildings

It has been underscored that the buildings that are located near the natural environment have higher chances to come under the demand list when compared with the buildings without such special factors.

The building designers are now promoting the incorporation of plants into the building envelopes as a part of environment sustainability movement. These are included in the roofs and the exterior walls, as these elements cover a large portion of the building structure.

There is a global increase in construction of high rise building in the past two decades. Many different ideas like the “Bioclimatic Skyscraper”, ” Eco Skyscraper” or the “Vertical Landscape”, which are ideas related to the greenery in the building design are evolved.

Green Walls in High Rise Buildings

The types involved in the green wall topology are the:

• Green Facades
• Living Walls
• Vertical Gardens
• Hanging Gardens
• Bio-shades
• Bio-Facades

What are Green Walls?

Green walls are systems in which plants grow on a vertical surface over the building facade, in a controlled pattern providing regular maintenance is termed as a green wall or vegetated facade.

The main elements that are involved in the construction of green walls are:

• The plants
• The planting media
• The structures that are used to support the plants and attach them to the façade
• The suitable irrigation system

Different Types of Green Walls in Building Construction

Based on the variation of elements used in the green wall construction, there are different types of the same:

1. Facade-Supported Green Walls
2. Facade – Integrated Living Walls
3. Stepped Terraces
4. Cantilevering Tree Balconies

Facade Supported Green Walls

Here the green wall system is supported off the facade at the area where the planting medium is not integral to the facade. The figure-3 shows the real example of a facade supported green wall.

Fig.3: Facade Supported Green Walls

This kind of system comprises of steel, wood or plastic trellises that are externally attached to the building facade. Here the climbing plants and the vines are supported with the help of horizontal, vertical or the diagonal trellis members.

A two-dimensional green facade system is formed by cables, ropes, and meshes. In the case of a three-dimensional system, rigid frames and the cages are employed.

Fig.4: Diagrammatic Representation of two and three-dimensional green wall system in the facade supported green wall

Facade Integrated Green Walls

The figure-5 below shows the facade integrated living wall.

Fig.5: Facade Integrated Living Wall

Stepped Terraces

In the case of stepped terrace, the concrete floors are used that hold the plant medium that is arranged in trays, within the infill walls. These advances in steps in the upward direction. This would finally seem similar to a terrace farming. This concept is used where plants of a large variety and that require large soil is used. This would behave as a green roof and a green wall.

Fig.6: Stepped Terrace in Building Construction

Cantilevering Tree Balconies

Some of the builders place a generous number of trees in the facade front area. This is achieved by constructing a projected balcony. These platforms will have the depth that is sufficient to support the root structure as well as the required amount of soil. These may have soils up to the level of the safety railing.

The weight of the soil and the tree are high that the structure is constructed by means of a reinforced concrete. These structures are then integrated into the primary structure of the building. The figure-6 shows an example of cantilever tree balcony in high-rise buildings.

Fig.6: Examples of High rise building projects with the idea of cantilever tree balcony

Benefits of Green Wall

Multiple benefits are offered by the design of green wall or the facade integrated vegetation. The factors that determine the benefits from the green wall are dependent on the:

• Geographic Location
• Climate
• Geometry of the building
• Orientation of the building
• Plant species
• Components of green wall and related system

The benefits can be categorized into two levels. One is the urban scale and the other is the building scale.

The Green Wall benefits in Urban Scale are:

The Urban heat island effect is reduced

The urban heat effect is a temperature difference that is caused by the between the urban centers and the countryside. The UHI effect is a serious issue to many cities. Due to many sources of heat like vehicles, industrial production, the mechanical equipment, and the building materials will radiate heat to the environment.

These heats are stored in urban canyons. The countryside has a lower temperature because of the presence of vegetation. The difference goes high to 12-degree Celsius making the occupants in the city to depend on amenities that cool buildings; which will result in high energy consumption and air pollution through the emission of greenhouse gasses.

The introduction of vegetation into the cities through a green wall or green roofs or parks will help in reducing the UHI effect. The plants that are grown will help in absorbing the large amount of heat which help in creating a micro-climate. These helps in increasing the humidity effects and shelter the building from direct heat and wind.

The air quality is improved

The process of photosynthesis facilitated by plants would transmit the carbon dioxide, water, and the solar radiation into oxygen and glucose. Building construction will occupy the horizontal space that is to occupy by plants.

This results in a reduction of oxygen production and hence the air quality. So, the incorporation of vegetation into the oxygen-deprived areas in the cities. This can be done using green wall systems.

Isolation of Carbon

Isolating the carbon in the form of sequestration is a capability that is owned by plants. Otherwise, these carbon are released into the atmosphere in the form of greenhouse gasses and carbon dioxide. The Vine based green wall construction help in such sequestration phenomenon. These plants do not demand high water and large space.

Aesthetic Appeal

The structures are embellished by the benefit of green wall system these are a concept more suggested by the builders to deal with aesthetics. Various plans are available with different texture and colors that can be skillfully arranged to decorate the building facade. Existing complementary spaces can be recreated by this method.

Psychological Impact

In addition to their aesthetic features, the green walls provide tangible relief from high sun radiation that is radiated from the building surfaces and streets. This would give a calming effect to the urbanites.

Improvement of biodiversity and creating natural animal habitats

The studies have shown that certain species of plants and animals are favored by the biodiversity obtained through the green building walls and the facades. Algae and lichens are some of these organisms. They also help the dwellers like mosses, ferns, liverworts and some coniferous plants.

Deadening of sound

The occupants of the buildings located in the cities face a huge problem of noise pollution hard surfaces tends to amplify the sound and get redirected. The Incorporation of thick vegetated green walls would reduce the deadening effect caused due to urban noises.

The Green Wall benefits in building scale:

Building Energy efficiency is improved

The thermal performance of the building is significantly increased by the facade plants. This will involve the increase of insulating property of the walls (mainly in colder regions), the facade shading property is increased ( mainly in hotter climates), the evapotranspiration will cool the air and also will reduce the wind near the facade.

Air filtration, air quality, and oxygenation internally is carried out

The plants will help in trapping the airborne particles from the atmosphere. Heavy metals, copper, lead, and zinc are absorbed by the plants. Builders suggest green walls improve the interior quality.

Benefits for health

Individual psychological and physiological health conditions are affected by the positive effects of green walls. This helps in bringing a visual connection for the occupants with the exterior vegetation.

This will help in giving positive emotions for the occupants. Breathing diseases suffering people are greatly benefited by the air filtering and the oxygenating abilities.

Protection of envelope

The wall is protected from the ultraviolet layer. This direct effect will cause the complete deterioration of the structure. The internal stresses within the wall are decreased by creating the temperature fluctuations.

Noise reduction internally

Sound attenuation qualities are highly gained by the green wall topology. The transmission of noise is transmitted into the interior of the building.

• Benefits for agriculture
• Property value is increased

Types of Curtain Wall System – its Details, Functions and Advantages

Curtain wall system comprises one of the elements of facade technology in high rise building. Facades involves window wall, cladding elements and curtain walls which generates the exterior envelope of the building.

The curtain wall systems now possess structural importance equivalent to that gained by other structural elements of the building. As it has a higher exposure to exterior atmosphere, it has to be properly designed, installed and maintained keeping in mind the functionality and sustainability.

Fig.1: Curtain Wall System

Fig.2: Curtain Wall Construction

Functions of Curtain Walls in Buildings

Elimination of Water Penetration

Water penetration is the fundamental function of a facade. Here bringing a completely impermeable sealed curtain panel system is not possible. Hence two stages of prevention are placed. Primary level where complete defense of water is conducted and if that fails a secondary level where a direction to let percolated water to drained out has to be provided.

Air impermeability

This function is more of an environment concern to reduce the emission of carbon dioxide due to rate of heat loss or gain within the external and internal environment.

Resistance to wind, thermal and acoustic action

Wind actions are transferred by the cladding system to the building floors which act as a linear support. Building cladding systems formed of large panels are usually one-way spanning. Each floor level therefore supports one level of wind load on a building.

Thermal insulation function which is strictly necessary for a facade in order to reduce energy consumption and CO2 emissions. Insulated materials are provided to both opaque as well as transparent areas.

Acoustic Insulation too is necessary between the inside and the outside environment mainly city centered building. Massive structural elements possess higher acoustic insulation like masonry or concrete structures.

Solar levels

This can be reduced by providing a selective solar control coating on one of the surfaces of the glass. This coating is called selective because solar radiation of different wavelengths is selectively allowed to pass through the coating: visible wavelengths of light are allowed to pass more freely than infrared wavelengths. For example, spaces for exhibitions or displays of materials can undergo degradation due to ultraviolet radiation. For this a UV-inhibiting film can be applied to the surface of glazing.

Types of Curtain Wall System

Curtain wall systems are factory pre casted systems. They are bought to the site and assembled. These are of two types based on the way each component is assembled.

• Stick Curtain Wall System
• Unitized Curtain Wall System

Stick Curtain Wall System involves its components to be assembled piece by piece on the building at the site. These are mainly installed in low rise building or small regions. This is because, to reach higher elevations exterior access is essential. For this additional requirements like scaffolding, cranes etc. will be required.

The above system gains the advantage of low shipping cost as onsite adjustments are possible. But the time and labor consumption is recorded to be high.

Unitized curtain wall systems involves assembling by means of interlocking units that are bought from the factory. The whole components are bought together as a single unit from the factory. Individual installation of each component are not necessary as in sticky curtain wall system. The size of the unitized curtain walls are dependent on the floor to floor height of the building. Hence it is essential to keep in mind the mode of transportation and installation while planning the depth of facade. This system is mainly used in high rise building. This does not require exterior supports like cranes or scaffolding. Only mini cranes or a temporary hoist can be held over floor to keep it help during installation.

This system gains advantage of faster construction and higher quality because of factory manufacturing. But it gains high shipping charge as mentioned due to requirement of larger protection during transportation.

Components of a Curtain Wall

The complete unit consist of the following structural elements

1. Transom
2. Mullions
3. Vision Glass
4. Anchor

Fig.3: Detailed Components of a Curtain Wall System

Fig.4: Mullions and Transoms

Transom or horizontal rails are horizontal members on the curtain wall panel. The mullions or vertical rails are anchored to the edge slab or beam. These are mainly involved in supporting the dead weight of the curtain wall. In conventional or sticky curtain wall system each system has to be placed one after the other. High quality check and precision in required for the installation. But in unitized system the factory product comes as two units alone which has to connected.

Panel Framing details of Curtain Walls

Unitized system is identified by the split mullions and the transforms that are evident in the panel perimeters as shown in figure.5.

Fig.5: Unitized Curtain Wall

In case of sticky curtain wall, there is no sort of splits all forms a single unit. During Longer spans, there will be a need for intermediate transom which would essentially split the entire vertical panel into two.

In order to prevent condensation, mullions and transom are thermally broken. This prevents cold bridging.

Weather Tightness of Curtain Walls

The weather tightness mainly deals with the issue of water permeability. In order to avoid this impermeable insulating units (glazed units) are employed. In addition to which a gasket is provided which leads to a rebate. Any water that moves into the gasket is lead to the rebate which in turn is drained out through the transom joints or mullions ends.

Support Conditions of Curtain Walls

As discussed curtain wall systems are hung from top which are laterally supported at different floor levels. Most of the supports are held at the edge beams. Hence it is essential to have a highly stiffened edge beam in order to avoid larger deflections.

These vertical deflections could disturb the whole curtain system. So proper edge beam provision would prevent damage to the curtain wall and cladding system particularly when it is highly glazed.

As an alternative steel strong backs can be provided so that they can span between the perimeter columns and hence it is not necessary to connect to the edge beams or floor slabs. The strong backs are mainly hot rolled sections.

Structural Behavior of Curtain Walls

Past studies have showed that curtain walls seem to be resistant against lateral forces mainly earthquake, but there is measurable amount of damage caused. Even though damage can be repaired, there is economy loss and delay in business activity.

Curtain walls are considered as structural elements of a building. As it acts as a partition between exterior and interior environment of the building, it has a role in transmission of loads acting for structural stability.

It transmits wind induced loads to the primary structure. It also resists the seismic accelerations keeping the occupants comfortable. Other than this it has to resist gravity loads coming over it.

When considering the durability of the building, curtain walls play an efficient role in adapting to different temperature ranges. This is because of the case in high rise building, as the number of floors the temperature seems high and would be a risk factor for the occupants working in those floors. It is also required to have resistance against water penetration and hence stop corrosion.