Developing a roof slab insulation system for tropical climatic conditions

Abstract

Global Warming is proven to be one of the biggest issues that the current world is facing. Greenhouse gas emission due to the extensive energy usage has been identified as the primary cause for that. Hence, the world is on its path to investigate ways and means of reducing energy consumption in the world. On the other hand, due to the rapid urbanisation took place in recent history, land prices have escalated significantly. Hence, flat roof slabs become popular day-by-day due to the possibility of land recovery by that. Further, it has many additional advantages like cyclonic resistance, the possibility of future vertical extension and the possibility of utilising as an extra working space. However, a serious matter of concern is its thermal discomfort, for which air-conditioning the corresponding spaces is the most common remedy used. However, it has led to extensive use of energy, increasing the operational cost of the buildings and contributing to global warming, which is the issue that the world is attempting to mitigate. Hence, the current trend is to go for passive techniques. In this process, insulating roof slabs has been identified as a better passive way to make buildings thermally comfortable. In this study, several existing roof slab insulation systems and their performances were investigated, and the most efficient system for tropical climates was identified. Since that system had an issue in durability as it had poor drainage arrangement, an optimised system with a structural arrangement of discontinuous strips was found out by computer simulations. A physical model developed to verify the results showed that the newly developed system could withstand a point load of 4MT at its most critical locations. A comparison of thermal performance between the new system and the existing system was carried out by small-scale model testing. It resulted in finding that the newly designed system performs better than the most recent and efficient existing insulation system. An actual scale model testing was carried out to check its performance under real conditions. The results suggested that this newly developed system performs well in thermal aspects under actual conditions, and performs better than even a calicut tiled roof with a timber ceiling. Results suggested that this system can produce a peak cooling load reduction of about 20%. The performance of an air gap as an insulator was checked in the process of trying to replace the insulation material and found out that air gap is marginally less effective than polystyrene. Further, it was proven that the thickness of the air gap does not have a significant effect on the thermal performance. Further, a confined air gap with bamboo strips was also proven to have a similar thermal performance. An added vegetation layer on these systems further enhanced the thermal conditions of the building. A life cycle cost analysis suggested that the overlaid vegetation performs slightly better than the cases without vegetation in economic aspects. But the life cycle costing values lie in the same order, proving that all the systems considered are almost equally effective in terms of economic performance. However, due to the advantages like local and natural availability, bamboo, as an insulation material, is very favourable to be used in local context.