At present, the world is facing many hurdles due to the adverse effects of climate change and rapid urbanization. A lot of rural lands and villages are merged into cities by citizens, resulting in high carbon emission, especially in the built environment. Besides, the buildings and the construction sector are responsible for high levels of raw material consumption and around 40% of energy- and process-related emissions. Consequently, the interest in defining the carbon footprint of buildings and their components is on the rise. This study assesses the carbon footprint of a green roof in comparison to a conventional roof in a tropical climate with the aim of examining the potential carbon emission reduction by a green roof during its life cycle. A comparative case study analysis was carried out between an intensive green roof and a concrete flat roof located on two recently constructed commercial buildings in the Colombo district of Sri Lanka. Data were collected from interviews, project documents and past literature in addition to on-site data measurements and a comparison of life cycle carbon emissions of the two roof types was carried out. The results revealed that the operational phase has the highest contribution to the carbon footprint of both roof types. In the operational phase, the green roof was found to significantly reduce heat transfer by nearly 90% compared to the concrete flat roof and thereby contributed to an annual operational energy saving of 135.51 kWh/m2. The results further revealed that the life cycle carbon emissions of the intensive green roof are 84.71% lower compared to the conventional concrete flat roof. Hence, this study concludes that the use of green roofs is a suitable alternative for tropical cities for improving the green environment with substantial potential for carbon emission reduction throughout the life cycle of a building.
As a result of increased attention towards sustainability worldwide, green concepts have become popular in the construction industry. Green roof is one of the essential elements in a green building that provide many advantages while creating a pleasant appearance for the total building. Green roofs play a major role in energy saving of a building. However, compared to a conventional roof, the initial and maintenance costs of a green roof is quite high due to the additional construction and high maintenance requirements. Thus, this paper compares the Life Cycle Cost (LCC) of a green roof with that of a conventional ceramic tile roof in order to determine the financial viability of green roofing. Findings were gathered from several cases and past researches under initial cost, maintenance cost and energy saving of green roofs and adopted to the selected case for the analysis. Findings of the study indicate that initial cost of the green roof was higher than conventional and represented 8.39:(-6.55) proportion of the total life cycle cost of the building. Similarly, maintenance, operational and replacement costs were also higher than the conventional representing 12.08:(-6.55) proportion of the total life cycle cost of the building. Green roof also had higher energy cost than the conventional, representing (-23.64):(-6.55) proportion of total life cycle cost of the building. As a result, it was found that 654.70)/m 2 net saving by a green roof is considerable despite of the high initial and the maintenance cost. According to the study, green roofing concept is financially and environmentally beneficial concept even though there are some barriers, like lack of knowledge, lack of techniques, lack of standards in implementing this concept in the Sri Lankan context. Hence, it is recommended to use green roofing in residential buildings.
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