Advantages And Disadvantages Of Green Roofs

Gardens that are constructed on the roofs and balconies for growing plants ranging from flowers to vegetables are called terrace garden. The trend of constructing a terrace garden is not something new and its origination dates back to thousands of years ago during the civilization of Mesopotamia.

“Ziggurats of Mesopotamia” which were constructed between 4,000 – 600 BC had no inside rooms, trees, and blooms on each porch of the gigantic ziggurats would give a cool, obscure spot for the guest to rest from the bursting Babylonian sun.

The Hanging Gardens of Babylon are one of the Seven Wonders of the Ancient World and maybe the most acclaimed of rooftop gardens.. It was built during eighth to sixth century BC. Notwithstanding, the latest patterns in rooftop nurseries are both environmental and handy. Nowadays the possibility of the rooftop nursery has been changed into the green rooftop As a result of the fast expansion of human civilization, all the forest, fields, and grasslands are being substituted by concrete and steel resulting in high pressure on the land.

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With the growing pressure on the land, the concept of terrace gardens has been gaining a lot of recognition.

At the present time, the most significant phenomenon related to high temperatures in most places is the “Urban Heat Islands (UHIs). An urban area that is considerably warmer than its surrounding rural areas due to human activities is called urban heat island. The effect of UHI can be mainly felt in summer and winter.

The four main reasons for the phenomenon of urban heat island are:

  • The change in thermal properties of the earth surface
  • Buildings being an obstacle to the wind flow
  • Change in moisture condition due to urbanization
  • All the heat and pollutants emitted into the environment due to urbanization.

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Lately, people have become more concerned about the effect of urban heat islands and are looking for ways to minimize the effects. Many researchers have been done trying to develop techniques and construction materials that will absorb less heat. It is unrealistic to demolish all the existing buildings so as to rebuild them using the new technique and materials. Terrace garden in its own small way helps in reducing the urban hear effect. (Alhashimi, Aljawi, Gashgari, & Alamoudi, 2018)

Apart from terrace gardens resisting the urban island effect, terrace gardens are also advantageous in reducing the rain runoff.

Types of Green Roofs

There are three major types of green roofs according to FLL guidelines: extensive, and intensive based on the specific green roof assembly and load characteristics.

Extensive Green Roof

It is the cheapest of the three types of systems. It is designed as an ecological roof garden instead of a luxury space. The depth of the substrate range from 0.8 to 6 inches. Only low growing herbaceous plants, such as mosses and grasses are grown in this type of roof garden. (No Title, 2010)


  • Lightweight, no reinforcement is required on the roof
  • Suitable for large areas
  • Less maintenance and longer life
  • Looks natural


  • Energy efficiency is less
  • Choice of the plant is limited


This type of roof system basically imitates traditional gardens at ground level. The media is usually more than 8 inches. This type of roof garden can grow trees, herbaceous plants, and lawns.


  • Wide range of plants
  • Good insulation properties
  • Less maintenance and longer life
  • More energy efficient.


  • Load on the roof is more
  • High investment and maintenance cost.

Considerations for Establishing Roof Garden

Before setting up a rooftop garden, we should think about after perspectives:

  • State of the rooftop:

The best time to develop a rooftop garden is the point at which the rooftop is recently built or being fixed. When working with a current rooftop, we should consider the current leakages, damage, failure to oppose roots and standing water and so forth.

  • Structural capacity of the rooftop:

Preceding structuring and building a rooftop garden, we should decide whether the rooftop can withstand the extra weight of soil and plants. The structural limit of the rooftop mostly decides the sort of rooftop garden that can be assembled.

  • Access to the rooftop:

Access to the rooftop is a significant consideration. Normal access incorporates stairs or emergency exits. Be that as it may, there must to be sufficient space for shipping materials for development and upkeep.

  • Weight of garden:

Thought of weight is the core of getting ready for a rooftop garden. Weight of the garden ought to be controlled by authorized planner or basic designer. It must be guaranteed that the weight of the garden doesn’t surpass the basic limit of the rooftop

  • Cost

Before beginning a rooftop garden, all essential cost examination must be done. Usually, green rooftop costs half higher than ordinary rooftops. Also, an extensive garden is less exorbitant than an escalated garden. (Consideration, 2009)

  • Plan of a rooftop garden:

The plan of a rooftop garden may differ with the structural capacity of the structure, proprietor’s close to a home decision, the motivation behind cultivating, surrounding scenery, and so forth.

  • Water system:

Rooftop nursery plants to a great extent rely upon downpour water for the water systems. Be that as it may, during a certain time of year, precipitation might be lacking to satisfy the water necessities. So, harvesting of downpour water should be possible. In addition, trickle water system framework, hose-pipe manual watering, and so forth ought to be masterminded to enhance precipitation.

Components of Green Roofs

Green roof assemblies are common of two systems of two systems i.e. roof base and above membrane vegetated roof system. The roof base is made up of a waterproofing membrane, rigid insulation, protection, and structural system. The vegetated roof system consists of eight functional layers: vegetation, engineered fill, insulation, filter fabric, drainage layer, root barrier, waterproofing membrane and structural support. The requirements of these layers depend on situations, some layers may not be needed in some situations whereas some situations require additional layers. ( Engineers & Angeles, 2008)

Anatomy Of A Typical Green Roof Assembly

  •  Vegetation: The landscape of the place plays a vital role in the selection of green roof plants. A dead load of ground vegetables ranges from 2 to 4 psf. Appendix A shows the additional design dead loads for different green roof types and plants.
  • Growing Media/ engineered soil layer: The depth of the growing media depends on the type of plant selection.
  • Insulation layer: this layer is either laid below or above the waterproofing membrane. When the insulation layer is laid below, the system is considered as an inverted roof membrane assembly (IRMA). This system takes benefit of the insulation layer to protect the waterproofing membrane from puncture and UV degradation. The compressive strength of the rigid insulation board must be sufficient enough to take the load. Despite the fact that a green roof can serve as an insulating layer, it has been recognized that climates having extended periods of winter will still require an insulation layer. (Scholar & Engineering, 2019)
  • Filter/Separation fabric a none clogging, synthetic filter fabric (nonbiodegradable) is installed to maintain the drainage and water storage capabilities of the drainage layer. The filter fabric should be made of a structure that resists clogging from fine soil particles. Generally, this filter fabric is only about 1/8 inch thick.
  • Water storing drainage layer: this layer basically has two competing characteristics: 1) Drainage of water from the plant root zone 2) storage of water to provide plants with moisture during periods of dryness. The three main types of drainage layers are 1) Drainage plates 2) Granular media and drainage mats.

Drainage plates are the waffles rigid thermoplastics that are simple to install and various sizes are available. The drainage plate system is usually about 1 inc to 2-.5 inches tall. Granular media system consists of a base layer of lightweight, inorganic, granular media. This granular media is composed of porous lightweight aggregate. The granular media system is about 2 to 6 inches. Drainage mats are the thinnest, lightest and quickest to install. This system consists of a multi-fabric mat that combines sol separation, drainage, and protection functions. The only disadvantage is its limited water storage and drainage capacity. Its thickness ranges from 3 to 8 inches. (Shafique, Kim, & Kyung-ho, 2018)

Drainage Layer System (Resource Conservation Technology 2006)

  • Protection fabric: This layer is t typically placed above the waterproofing and root barrier membrane. The main function of this membrane is to prevent damage during construction and roof maintenance activities. Protective fabrics with water storage and capillary capabilities can also be designed.
  • Root protection barrier: some waterproofing membrane likes bituminous and asphalts are not resistant to root penetration or degradation. Root barriers are usually made of PVC and sometimes contain release agents. The thickness of this layer range from 0.03 to 0.04 inches.
  • Waterproof layer: it is a vital part of the system if we want a long-lasting and maintenance-free life of the green roof.

Beneficial Impact of the Roof

  • Reducing the urban heat island effect

Urban heat island is the overheating of the urban areas compared to the surrounding rural areas which are due to the increasing human activities. Introduction of greenery through green rooftops in the urban zones can lessen impenetrable surfaces and mellow streetscapes. Plants use heat vitality for evapo-transpiration to accomplish a cooling impact. By diminishing the warmth increase through the rooftop encompassing temperature is brought driving down to less vitality utilization .Internal structure temperature by 0.5?C. It also decreases the power consumption for air conditioning.(Bahru, Rashid, Hamdan, & Ahmed, 2009)

  • Roof life span

Green rooftops help to shield material films from extraordinary temperature vacillations, the negative effect of bright radiation.

  • Aesthetic advantage

Green rooftops can assume a significant job in giving recreational spaces in urban locales where there is little ground-level green territories. As these spaces are noticeable from numerous vantage focuses, it adds to the visual character of the urban texture.

Energy Proficiency And Temperature Control

The more noteworthy protection offered by the porch nursery can diminish the measure of vitality required in a structure.

  • Food generation

Rooftop surfaces offer the open door for developing nourishment, especially in high thickness urban regions where nursery space might be constrained. – nourishment creating plants can substitute for elaborate plants in customary rooftop gardens.

  • Air cleaning

Green rooftops channel out fine, the airborne particulate issue as the air ignores the plants. Airborne particulates will, in general, get caught in the surface territories of the greenery.

  • Sound protection/controls commotion contamination.

Hard surfaces of urban regions reflect sound and can’t ingest it. Green rooftops because of the vegetation retain sound waves(Mahdeloei, Farahani, & Shakori, 2012)

Negative Impacts of the Roof Garden

Roof Garden Weight and Structure

Most buildings and houses built before are constructed with brick and concrete or with a cement frame. Engineers and designers did not think of foreseeing the installation of a green roof at that time. A discussion with the original constructors on roof loading is necessary when arranging the establishment of a housetop garden. There are two types of roof loading:dead load and live load. Dead load refers to the weight of the roof structure itself and any permanent structures on that roof. To accommodate weights beyond the dead load (from snow or rainwater), buildings are normally designed with a “live loading capacity”. This is meant to bear the weight of snow in the winter, but rooftop gardeners can use it during the summer, take into account the total weight of the roof garden and the retained water. Unfortunately, most formerly constructed roofs are not designed to support an intensive garden with a massive substrate layer and big plants. Only an extensive garden, with a thin layer of soil, mosses, herbs, sedum or other succulent plants, seems appropriate here. On the contrary, a modern building’s roof should always be planned to support the weight of a roof garden. (Sharma et al., n.d.)

Soil and planting pots are both substantial – regardless of whether you make a dirt planting bed in your rooftop nursery or use pots, you are essentially including to the weight put the rooftop structure. Yard sections and furniture further include the weight of the rooftop. Most building rooftops will require appropriate fortification before a rooftop nursery can be developed securely. High rooftop nurseries may have issues with high breezes harming plants and youthful seedlings.

Water Supply

Typical gardens at the ground level, built-in recently created pieces of the city, may experience some difficulty getting to the water. Tops of current buildings, in differentiate, are quite often near conceivable stock of city water or faucet water from the top floor. However, collecting precipitation water for plant creation is more fitting than utilizing urban water.

On the contrary, in more established pieces of the cities, irrigation frameworks for watering plants in a rooftop nursery might be absent, which makes its upkeep very difficult. Therefore, one ought to right off the bat search for a decent answer for this serious problem. Here, the TC-strategy to stock water in the root zone can help in a huge manner.

Discovering conceivable outcomes to reap and store downpour water ought to consistently be a need for anybody building up an urban nursery. It is staggering how brisk the dirt of a rooftop nursery is drying out and plants will shrivel all the time if standard watering, early toward the beginning of the day or late in the evening, is overlooked. During mid-year, watering ought to never be done in the day.

As low yearly precipitation is influencing straightforwardly plant development in a rooftop garden, it can be important to approach the metropolitan water supply, e.g. for the dribble water system.

Gathering precipitation water for the ulterior water system can represent a problem, as there is commonly no appropriate space to store an enormous vessel. To give satisfactory weight in the dribble water system framework to be imagined, a gravity-bolstered hose will require a stock tank introduced a lot higher than the hose outlets. Another issue would siphon faucet water into this inventory tank in the event that it was arranged on a similar rooftop. The heaviness of the tank would need to be appropriated equitably over a significant zone to arrive at the live-load farthest point of the rooftop. These variables can make the water system framework and water accumulation impractical. The issue waterway so comes at the opposite finish of the spectrum, i.e. there could nearly be an excessive amount of water.

Therefore, one ought to ideally search for a satisfactory framework to improve the water maintenance limit of the substrate so as to stock consistently adequate volumes of water to maintain a strategic distance from dry season pressure. The conceivable excess of water during tempests ought to be effectively depleted. The amount of water held in the substrate must be promptly accessible to the plant roots to abstain from the shrinking of the plants over a more drawn out dry period.

Perhaps the best technique to stock water and manure in the substrate of a rooftop nursery is called theTerraCottem-or TC-method which was created by the college of Ghent(Belgium)in1983-1992. It has been applied since 1995 in China (Greenhouse venture in Lanzhou, Gansu Province) and it has demonstrated its viability in various Chinese regions from that point forward. The TC soil conditioner is a blend in excess of 20 granular substances, all helping plant development in a synergistic way. These substances can be separated into 6 gatherings:

  1. Water retentive polymers
  2. Soluble mineral manures
  3. Slow discharge mineral composts
  4. Synthetic natural composts
  5. Carrier material (volcanic shake or “magma”)
  6. Growth activators for roots

Small amounts of the TC, mixed into the root zone, have a few constructive outcomes:

  1. Improvement of plant and root development
  2. More blossoms
  3. Reduction of the volume and recurrence of the important water system
  4. More opposition of plants to withstand times of dry season pressure
  5. Activation of the microbiological action
  6. Reduce upkeep costs

Layer Installation

In the event that a rooftop garden has soil beds, a defensive layer should be introduced between the dirt and the structure’s housetop. Introducing this layer is an expert activity and can be costly. Rooftop garden films can progress toward becoming debased after some time or cracked by screws, nails or the utilization of digging tools. A cracked layer can breakwater and soil into the structure. Redesigning or supplanting the film may require total expulsion of the rooftop garden, which interferes with you to the starting point regarding nursery arranging and plant improvement

Protection and Safety

There is a high chance that your structure having a rooftop garden, odds are that insurance agencies will charge a higher premium than they would to cover a similar structure without a rooftop garden. More noteworthy protection expenses speak to another manner by which a rooftop nursery is frequently more costly than a normal nursery. Rooftop nurseries might be riskier than normal nurseries, because of the danger of falling. On the off chance that you have – or welcome over – youngsters to your rooftop garden, guarantee the edges of the nursery are blockaded so no one can tumble from the rooftop.

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Advantages And Disadvantages Of Green Roofs. (2019, Nov 16). Retrieved from

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