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Optimising the substrate layer for the implementation of Green Roof in Commercial Space Green roof is a flat or pitched roof surface that may or may not have been fully covered by cultivating vegetation over a waterproof and insulating membrane (Downton, 2013). Not only does a green roof increase the buildings overall efficiency but it also helps in creating a sustainable environmental balance. There are various underlining parameters that affect the heating and cooling in a building while implementing green roofs. Type of the material, plant type, soil, factors relating to their maintenance (Saadatian et el., 2013), thickness of different layers that constitute it, amount of vegetation on the soil, irrigation, the local climate (Sailor, 2008), moisture content and age of the building (Castleton et el., 2010) have a positive co-relation in deciding the effectiveness of a green roof. According to Ascione et el., (2013), green roofs act as an ideal energy saving mechanism in hot and humid climate because of its tendency to cool. It actually consumes more power during winters due to heating requirements. With that being said, Reyes et el., (2016) concluded that as we increase the thickness of the substrate layer in a green roof in arid and semi-arid regions, it's cooling capacity increases. Additionally, the substrate material also plays a crucial role in achieving optimisation. Vijayaraghavan et el., determined that by mixing various organic and inorganic materials such as perlite, vermiculite, crushed brick, sand and coco-peat in appropriate proportions present remarkable features such as high water holding capacity, hydraulic conductivity, low bulk density, maximum plant support and air filled porosity can be expected. It is also a better option to consider commercially available substrate instead of using a mixture of locally procured compost and soil as it leads to problems such as overweight of the green roof, growth of unwanted weeds and poor water retention, increasing the overall weight of the green roof by jeopardising the safety for old commercial spaces (2014). Moreover, a lower density substrate would enable the roof to grow a wide range of vegetation (Xiao et el., 2014). In contrast, a certain amount of organic material is essential for the plant growth and supply necessary nutrients. According to Forschungsgesellschaft Landschaftsentwicklung Landschaftsbau (FLL), a German standard for green roof, 6-12% of organic matter must be used by volume to creating an effective substrate layer (FLL, 2002). While looking at the shortcomings of using organic matter in building a sustainable substrate, the high sorption capacity of organic matter cannot be neglected especially during extreme climatic conditions such as storms as the inorganic matter have a tendency to float in water (Vijayaraghavan K. , 2016). Vijayaraghavn et el., highlighted the use of seaweeds and algae to remove contaminated water during heavy rainfall. Being an organic material, it can also be used as a binding agent for the soil and possess essential nutrients for growth (2015). At the same time, the survival of a green roof substrate during drought remains a big question as it is imperative that the substrate layer has a substantial water holding capacity. There are several additives that can be used to improve the water holding capacity of the substrate (Vijayaraghavan K. , 2016). According to Cao et el., using biochar as an additive not only improves the water holding capacity (WHC) but also has a positive effect on the plant available water (PAW) (2014). Similarly, Farrell et el., suggested to add silicate granules and hydrogel to improve those the WHC and PAW of substrate (2013). It is also very important for a substrate to maintain good aeration and flow properties in order to promote the plant growth and prevent roof leakage (Vijayaraghavan K. , 2016). According to FLL's guidelines, the air filled porosity (AFP) should be greater than 10% and the hydraulic conductivity should be greater than 3600 mm/h (FLL, 2002). Vijayaraghavan et el., concluded that by using 4-10 mm crushed brick particle with 28.3% AFP and 14,200 mm/h hydraulic conductivity improves the overall flow of the substrate. Moreover, materials such as expanded granules, perlite and scoria improve the AFP and hydraulic conductivity. They also mentioned about the direct proportionality between the size of particles and organic matter and the efficiency of the substrate (2014). With regards to the suitability of inorganic substrate in green roof, studies suggest its versatility towards a wide range of plant species. Rowe et el., concluded that 25 different succulent species support can be grown in a substrate that is prepared using heat-expanded slate, sand and peat (2012). Dunnett et el., used ZinCo substrate which is suitable for 12 different species including forbs, grass and sedum (2008). Conclusion In the light to the findings of this literature review, it is extremely difficult to create or select an ideal substrate as there is always a compromise in terms of its property. It become imperative to maintain the accurate proportion of organic and inorganic material in a substrate in an attempt to achieve favorable characteristics such as water holding capacity, low bulk density, hydraulic conductivity and air filled porosity. This literature review also indicates a few untouched areas within this particular field of study, whose consideration could greatly impact on re-inventing the substrate material. Having understood the important co-relation between the thickness of a substrate layer and properties such as the weight of the roof and the cooling capacity of the building, a co-relation between the thickness of the substrate layer in a green roof and the age of the building can be speculated. Also, with the results that are obtained, the disclosure of this relationship can be transforming in optimising the green roof design and maintenance facility. Bibliography Saadatian, O., K., S., E., S., Lim, C. H., Riffat, S., Saadatian, E., et al. (2013). 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