Extracting Optimized Detail of Green Roof for Decreasing Building Energy Consumption

A green roof which is created with purpose of converting dead roof spaces into a dynamic environment¡ are considered as private spaces. Green roof is a roof that covers much or all of the space with vegetation and soil or covered by vegetative medium. Limitations of energy resources¡ growing trend of energy consumption and adverse effects and irreparable damages to the natural environment are important concerns of urban. One way to reduce energy consumption of buildings is Garden Roof. If garden roof or green roof would be correctly designed¡ implemented by considering climate issues¡ it can help to reduce energy consumption. Also the growing trend of energy consumption is one of the major concerns for cities. Green roof has a significant role in urban ecological efficiency and quality of urban life. Green roofs have significant influences on the city scale. Plants because of their biological functions such as photosynthesis¡ sweating¡ breathing and evaporation beside a layer of soil¡ affect the environmental factors and improve the quality and quantity the surrounding ecosystem. Chlorophyll creation has a positive impact on the space of city while regional climate and indoor air of building have high impacts on it and its role in air cooling through preventing solar radiation. This air cooling made by reducing thermal fluctuations on the outdoor roof and increasing heat capacity of the roof will take place under the roof space in summer and increase heating rate in winter. However its effects are not significant in summer¡ plants positively will have effects on heat performance of roof in summer as they always keep amount of air around their roots and stems which act as a thermal insulation layer. Green roof includes the original layers of vegetation¡ growing media¡ Insulation layer¡ Drainage layer¡ Protection layer¡ Root barrier¡ Waterproof membrane that will vary regarding to the types of used materials¡ compositions of different layers¡ and quality impacts on thermal performance. In green roof¡ vegetation and growing media play main role in heating transfer and other layers¡ depending on their used materials¡ influence differently on total heat transfer of roof while the number of layers cannot effectively influences on heating ratio. Noting Vegetation type and thickness of the growing media basically are important in thermal performance of the green roof. Plants regarding to their biological functions (photosynthesis¡ sweating¡ breathing and evaporation)¡ create a thermal layer due to air storage through the plant’s foliages and roots and producig carbohydrates¡ lead to reduce heat transfer and follow temperature control of structure. In addition¡ according to the vegetation¡ expanded thicknesses of growing media can double the thermal effect of green roof. Studies show that the used materials in green roof systems and its implementation in European¡ American¡ Asian¡ and etc. due to the various potential and ecological benefits of green roofs¡ are defferent. The inappropriate use of fossil energies and non- standard construction of buildings which lead to thermal energy lost; by emphasis on thermal performance of green roofs¡ makes it more important for Iran. For this purpose to minimize heat transfer from inside to outdoor and contrariwise performance in winter and summer¡ suitable details are defined. In this survey after explaining green roof¡ the heat transfer component for green roof is analyzed with the hypothesis that mentions “we can design an optimized detail for green roof and add a layer to it to increase its thermal performance”. The optimum detail of green roofs to reduce heat transfer is compared with conventional green roofs. It is observed that defined defined detail¡ respect to conventional green roofs has desired effect on reduction of heat transfer between the roof and its underlying layers. The number of layers in optimized green roof decrease to three main layers of vegetation¡ growing media¡ and designed layer while using materials with low heat transfer coefficient or almost insulated ones. In addition its main factors include: speed and easiness in implementing¡ reducing loads on the building structure¡ reduction of layers numbers¡ low cost of implementation and more important than all¡ positive effect of designed detail on heat transfer reduction. In this article¡ research method in investigation advantages¡ standards¡ and thermal performance was qualitative¡ but the survey for extracting detail of green roof was quantitative. Methodology for investigating benefits of green roof was descriptive and qualitative while in parts related to software analyses¡ the quantitative approach and analytical methodology were used.