The present study investigates how different types of waste-based coating mortars, with varying thicknesses, affect thermal performance of buildings. Energy simulations were performed in 3 different Brazilian climates, assessing thermal performance through the Thermal Load (TL) and Degree-hour (DH) methods. The thermal performance improved with increased mortar thickness in cold and mild climates. In warm regions, the TL method demonstrated this effect, whereas the DH method indicated the opposite trend. The best results were achieved by 30-mm-CM-Polystyrene-Foam-mortar in cold climates, 30-mm-CM-Steelmakin-Slag-mortar in mild climates and 30-mm-CM-Polystyrene-Foam-mortar (TL method) and 30-mm-CM-Metakaolin+GlassWaste (DH method) in hot climates. The results demonstrated that the correct choice of residue-based mortars and the appropriate adjustment of mortar thickness can promote better thermal performance in buildings, reducing environmental impacts, saving energy, and improving user comfort.