The presented paper aims at thorough uncertainty analysis of combined experimental and computational approach for determination of equivalent thermal conductivity of highly perforated bricks. The thermal conductivity is determined using experimental guarded hot plate method. However, due to large dimensions of analyzed specimens, the measurement is influenced by experimental errors due to abnormal heat leakage. Therefore, numerical modeling of heat transfer is performed in order to quantify this leakage and the resulting value of thermal conductivity is subsequently corrected. The uncertainty analysis is essential part of presented approach leading to its justification. It involves statistical errors, measurement errors as well as results of merged sensitivity analysis. Within the frame of this paper, highly perforated clay brick without cavity fillings was investigated. The results indicated that accuracy of presented approach is very sufficient and combined standard uncertainty is lower than 10 %.