Huge amounts of cotton and fly ash wastes are disposed from countries all over the world. The majority of cotton wastes and fly ash wastes is abandoned and causes serious environmental problems. This paper presents a parametric experimental study, which investigates the potential use of cotton waste and fly ash combination for producing new low cost and lightweight composite as a building material. The physical and mechanical properties of concrete mixes having cotton waste and fly ash waste are investigated. The compressive strength, flexural strength, unit weight and water absorption values of the product satisfy the relevant standards. The thermal insulation of brick is also carried out. The cotton and fly ash wastes bricks house has been found to be superior to the concrete brick house for sustained comfortable indoor temperatures. The process undertaken can be easily applied in the current brick plants. It yields a lighter weight composite having potential to be used for walls, wooden board substitute, economically alternative to the concrete blocks, ceiling panels, sound barrier panels, etc.