to the residents. It is still debated whether the green roof will cause fire or it will reduce the chance of one. Some argue that, because the vegetation is about 95% water, the green roof actually reduce the chance of a fire. On the other hand, some argue that during autumn and winder when the leaves are dried up, fire hazard will increase then. A recent study has found, through mathematical model, that when the vegetation itself caught fire, the heat will penetrate down rather slowly, because the thermal conductivity of soil is low, and finally did damage the roof itself. Thus the key to whether the fire caught by the vegetation will damage the roof or not depends on the thickness of the soil. The study also found that by installing a gypsum layer beneath the soil layer, the possibility of damaging the roof can be greatly reduced. Additional structural load: Most old buildings were not designed for the extra roof dead load of the green roofs. If more energy is consumed in building the additional load bearing structure for the green roofs than the energy saved through insulation enhancement and water retention, it would be contradictory to the idea of energy conservation. By study, common green roofs types in the market would increase the load on the rood by 1.2 to 2.43 kilo-newton per square meter. Pervious (porous/permeable) paving Many pavement in the urban and suburban area are impervious, this likely would result the contaminated stormwater runoff. In pre-development area, averagely 50% of storm-water would result in evapotranspiration, 5% in runoff, and 45% in infiltration, whereas in post-development area, only 35% storm-water result in evapotranspiration, and 50% in runoff, and 15% in infiltration. This change has caused various problem, such as flooding, infrastructural damage due to rapid movement of water, and water contamination. By using pervious paving, however, the amount of infiltrated storm-water will be increased in post-development area, and the pollutants in the filtrated water can be reduced; thus the problem can be mitigated. In Low Impact Development 2008 Conference, ASCE performed two bench-scale study to examine the effectiveness of permeable interlocking concrete pavement in terms of water flow rate and the role of microbial colonies in pollutant removal in the micro-environment of porous pavement. The experiment shows 84% relative total suspended solids (TSS) removal on average, yet the increased relative removal over time suggests there is