This study introduces the thermal performance criterion C_TPunsteady and C_TPsteady as the parameters combining energy-efficiency evaluation for multilayered wall assemblies assessment for steady and unsteady-state. The proposed criteria focus on physical characteristics such as wall width, mass, internal heat capacity and u-value. The research identifies the “best” wall configuration, based on the C_TPunsteady and C_TPsteady criteria, as a 375 mm AAC D300 wall with Rockwool insulation. In contrast, the least efficient assembly was Wall type C, consisting of a 1300 kg/m³ brick wall masonry with Rockwool insulation. The paper highlights the importance of complex consideration of physical and thermal influencing factors for thermal performance assessment.