An enormous amount of coal combustion ash is generated by Indian power industries. The storage of coal bottom ash on land pollutes the environment and endangers living beings. This study aimed to assess the viability of utilizing coal bottom ash as a fine aggregate in concrete. The use of coal bottom ash in the production of concrete will provide a cost-effective and environmentally sustainable technique of industrial waste disposal and natural sand conservation. The mechanical qualities as well as thermal performances in tropical climatic conditions of concrete with CBA (coal bottom ash) with up to 40 % replacement of sand were promising. The durability of concrete that incorporates CBA as a sand replacement is just as significant as the mechanical qualities. In this work, a guarded hot box and thermal conductivity test apparatus are used to assess the overall thermal transmittance (U value) and thermal conductivity, respectively in Indian climatic conditions. Typically used roof samples of 500*500*100 mm dimensions with different percentages of bottom ash have been tested. The results showed a correlation between the percentage increase in bottom ash substitution for sand and a subsequent reduction in the U value.