Calculation of the maximum moisture buffering thickness of building wall layer of hygroscopic material

Hygroscopic material can be used to moderate the indoor humidity variation due to its moisture buffering ability. Many studies have been carried out to evaluate the moisture buffering potential of hygroscopic materials. However, there is little literature about the optimal thickness of hygroscopic material for building design. This paper presents a simple method for determining the optimal moisture buffering thickness (L_opt) at which the hygroscopic material has maximum moisture buffering capacity (MBC) at a certain moisture environment. This method involves the calculation of MBC value by using moisture transfer function and Fourier transform. A case study of the clay plaster shows that the MBC firstly increases quickly and then decreases slowly as the material thickness increases. There exists an optimal thickness at which the MBC is biggest. This method for calculating the L_opt of the hygroscopic material layer of building wall is validated against the published experimental measurements. In addition, the proposed simple method is also compared with the experiment-based method and traditional numerical method. The result shows that this method is simple and efficient while keeping high accuracy. This proposed method can be used for the determination of the optimal thickness of hygroscopic material in building design stage.