Improving our understanding of moisture and other durability-related properties of wood in building envelope performance prediction

IRG/WP 11-20468

Jieying Wang, P Morris

Building science has become an increasingly important field in recent years with rapid changes in construction methods, building materials and consumer expectations. The field has also been brought to prominence by a few large-scale premature building envelope failures in a few regions across the world. Considerable effort has been put into developing hygrothermal models to simulate heat, air, vapour, and water movements within and through building envelopes. A few have become popular design and research tools for predicting and evaluating durability performance of building assemblies. One of the building elements which have often been put under building scientists’ microscope is wood, given the traditional uses and the newly expanded use of wood in building systems. Therefore it has become more and more important to bridge the gap between wood science and building science and carry out interface research to understand the behaviour of wood in modern building envelopes. One simple example concerns the relationship between equilibrium moisture content (EMC) of wood and relative humidity (RH) in the environment. Pressure plate methods have been commonly used in building science laboratories to measure EMC under near-saturated RH conditions. It was found that this method could result in unrealistically high EMCs if there is a lack of understanding of the unique characteristics of wood structure. Meanwhile the commonly used assumptions of EMC under changing RH conditions based on simple sorption curves may lead to unrealistic prediction of service moisture content. Another example is related to the consequences of service moisture conditions. Hygrothermal models are often designed to predict durability performance such as mould/decay growth and metal corrosion based on the predicted humidity or moisture content. Realistic prediction requires realistic mould/decay data as well as appropriate application of the data for specific conditions. This paper reviews topics where the wood science community can usefully work with the building science community and help each other better understand wood and improve the wood use in construction.

Keywords: building envelope, hygrothermal models, sorption, mould, decay, interface research

Conference: 11-05-08/12 Queenstown, New Zealand

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