An attempt has been made to study the effect of coalash usage as partial replacement of sand in building envelop construction material, and the energy conservation aspect thereof. The experimentally obtained thermal transmission values through building envelope’s outer layer component, made of concrete and mortar of specified proportion was validated through simulation program and the overall energy saving by way of reduced cooling energy demand have been quantified for a typical residential building.This study emphasize three aspects in a row, such as i) energy conservation by way of reduced cooling demand in hot and humid regions, ii) utilization of coal ash without further storage in ash ponds of respective thermal power plants, thus avoiding earth, groundwater and air contamination, and iii) responsible management of sand, which is the second most used resource globally after water, since the same is being used at the rate faster than, it can be replenished naturally. By modifying the wall mortar mix and plaster with coalash in a residential building, located within Warm-Humid region in India, cooling energy consumption reduces by 4.03%, and combining the same with modified roof concrete mix with coalash, the same reduces by 6.39%. Further, by placing concrete tiles with modified mix as waterproofing measures, reduction in overall cooling energy demand stands at 7.47%, and applying SRI paint on that surface, the demand reduces drastically to the tune of 42.80%.