Presentation Content
§ Wood chemistry and structure affecting durability
§ Natural durability of Canadian species
§ Organisms attacking wood
§ Types of decay fungi
§ Factors necessary for biodeterioration
§ Time required for decay to occur
§ Decay characteristics of Canadian softwoods
§ Other influences on decay initiation
The first paper, Understanding Biodeterioration of Wood in Structures, provides an overview of the subject matter and refers to a selection of textbooks for more detail. It provides some essential background on wood structure and composition, the range of wood-inhabiting organisms and their effects on wood. The colonisation sequence, the conditions required for decay, and the rates of growth and strength loss are covered in some detail. The second paper, Moisture Problems in Vancouver Condominiums reviews the background to the recent epidemic of decay problems in southwestern B.C. and Forintek's short-, medium- and long-term response. In the short term, Forintek has been assisting in the work of the Building Envelope Research Consortium (BERC) designed to understand and deal with these problems. In the medium term, we have developed a combination of safe low-level chemical treatments which will provide OSB with the same fungal resistance as Douglas-fir faced plywood. This paper also describes the long-term project Decision Aids for Durable Wood Construction.
The ultimate goal of the project is to increase confidence in the durability of wood construction, and thereby lead to greater use of wood products in China. This report aims to assess wood-durability related climate, termite, and decay loads, to inform those building wood structures. Specifically a decay hazard map for exterior above-ground wood structures was refined and a termite map was updated. Based on the decay and termite hazards, four biological hazard zones were proposed: low hazard zone with low decay hazard and no termites, moderate hazard zone with moderate decay hazard but no termites, moderate hazard zone with moderate decay hazard and Reticulitermes, and severe hazard zone with severe decay hazard and both Reticulitermes and Coptotermes. It is hoped that the information can be used by designers and builders as a general guide for designing for certain climate loads and biological hazards, and such a classification will pave the way for developing appropriate requirements for wood protection against decay and termites in different regions in China. The report also sends a strong message that compared to North America, China has a much larger area with a severe or moderate hazard. Hence proper wood protection is critical for achieving durability of wood construction.
The Scheffer Index for wood decay potential above ground provides guidance in planning design and treatment strategies to ensure the durability of wood products. Work to improve its predictive capability was sidetracked by finding values calculated from recent climate data were higher than those from the literature; likely a result of climate change. This led to development of an updated North American decay hazard map for comparison to a map created using published data. We found considerable expansion of the moderate decay hazard zone, particularly in the interior wet belt of British Columbia, across the northern edge of the Prairies and around the Gulf of St. Lawrence. Experience with decay of pine shakes in Edmonton suggests this may have practical implications for the durability of wood in service. It may also affect decay of woody debris and standing dead trees such as those killed by the mountain pine beetle.
Western redcedar (WRC) is renowned for its high durability, which is due at least in part to the presence of extractives that are toxic to decay fungi. Western redcedar's naturally low equilibrium moisture content (EMC) may also be a protective factor, since fungi typically require 30% moisture content to grow. Extractives are thought to contribute to the low EMC by blocking water adsorption sites on the wood. The present work compared the EMC of extracted and un-extracted WRC heartwood and sapwood. Extracted WRC heartwood had higher EMC than un-extracted WRC heartwood in samples not affected by fungi, and WRC sapwood had higher EMC than adjacent heartwood. The presence of extractives was identified as being associated with the low EMC of WRC heartwood in these samples.
