Qualitative work to study water movement in wood Dominique Derome, assistant professor. Building Envelope Performance, Laboratory, Department of Building, Civil and Environmental Engineering, Concordia University, 1455 de Maisonneuve blvd West, Montreal, Qc, Canada, H3G, 1M8, derome@alcor.concordia.ca Staf Roels, associate professor, Department of Civil Engineering, Laboratory of Building Physics, Katholieke Universiteit Leuven, Kasteelpark Arenberg 51, 3001 Leuven,Belgium; hans.janssen@bwk.kuleuven.ac.b, http://www.kuleuven.ac.be/bwf Jan Carmeliet, professor, Department of Civil Engineering, Laboratory of Building Physics, Katholieke Universiteit Leuven, Kasteelpark Arenberg 51, 3001 Leuven,Belgium; jan.carmeliet@bwk.kuleuven.ac.b, http://www.kuleuven.ac.be/bwf also at Faculty of Building and Architecture, Building Physics Group, T.U.Eindhoven, The Netherlands KEYWORDS: wood, X-ray projection, liquid water transport, water vapour transport SUMMARY: Wood in building wall assemblies may come in contact with liquid water. Rain, as the main source of water, is expected to be shed by the wood cladding. Improper detailing may result in water entering the wall, reaching the wood sheathing or even the wood frame cavity. Traditional methods like capillary uptake provide some indication of the process of liquid movement in wood but cannot convey the role of the wood structure in the water entry, redistribution and drying processes. This paper presents qualitative results using X-ray images to view moisture distribution within wood during liquid uptake. The microstructure of wood and the direction of grain are shown to influence the pattern and rate of moisture movement. 1. Introduction When it comes to study liquid movement, wood is a complex material. Capillary movement depends of the diameter of pores, on the connectivity of pores (through bordered pit pores) and the direction of grain. Cell diameter and the number of bordered pit vary from earlywood to latewood. Also wood is orthotropic and the movement of water in the longitudinal, radial and tangential directions varies in terms of mode of distribution and rate. Liquid movement is accompanied by redistribution by vapour diffusion. Diffusion in wood is also a complex phenomenon as diffusion occurs through air (in pore voids) and through cell walls, and the rate of diffusion is affected by local moisture contents and temperature gradients. Furthermore, moisture content change below the fibber saturation point is accompanied with change of volume. Therefore, there is still a need to better understand liquid water uptake by wood, moisture redistribution within wood and drying of wood. As the study of moisture movement in wood must therefore take into account the structure of wood, this paper first presents some basics information of the structure of two species of wood. The method of using X-ray to measure moisture content is presented and the qualitative results on two wood species are presented. A discussion on further work needed in this area completes the paper. 2. Structure of wood Wood has three material scales (FIG. 1):