Quantitative Study on the Moisture Properties of Japanese Cedar-Estimation of Moisture Permeability Using the Cup Method

Wood is a common porous material used in building interiors. It is therefore expected to adjust water vapor levels in indoor spaces. To examine humidity adjustment by wood, it is necessary to measure its moisture permeability, and to quantify humidity adjustment by wood, the accurate measurement of moisture properties is critical. This paper focuses on the measurement of the moisture permeability (λ’) of wood (Cryptomeria japonica). First, the measurement theory of the cup method and the error estimation method are described. Then, the moisture-permeability measurement results for the wood are presented. In the cup method, removal of the permeation resistance of the cup (R’ cup) was important to estimate the λ’ of the materials. In particular, in the material with low moisture-permeation resistance (e.g. wood shaving), the effect of adding the R’cup was significant. The relationship between average relative humidity(H) and the moisture permeability was experimented. The results of the linear approximation are: Moisture permeability of board: λ’board = 10-6？e0.0398H [kg/(m？s？Pa)], Moisture permeability of the wood shavings: λ’wood shavings = 9.88？10-6H+1.20？10-4 [kg/(m？s？Pa)]. The moisture permeability of wood shavings of cedar was about 10 times that of the cedar board. It is therefore confirmed that moisture permeability can be increased by changing the shape of a wooden material