The use of preformed modular walling units is a construction approach that is seeing more abundant use and is becoming a widely available method. Preformed units are usually a composite structure which often include a range of bio-based materials such as timber, wool or straw. This construction method has a number of advantages such as speed and uniformity of the structure.
However, as with all biobased materials the risk of microbiological attack is ever present, and dealing with this risk must be an important part of the design of the modular elements. When looking at durability of biobased materials the standard approach has been to look at methods used for the most ubiquitous biobased material used – ie wood. There are a number of methods available for determining the durability of wood based materials to the action of decay fungi e.g EN 113. However, these may not always be the most appropriate tests for non wood materials, although they will provide some information (Curling et al 2015).
One area that that traditional laboratory based tests do not take into account is the combination of biobased materials, as may be seen in modular constructions. It is possible that non wood materials such as plant or animal fibre insulation may act as a moisture reservoir or moisture buffer for wooden structural elements with a consequential effect on their durability. This could be seen as a synergistic relationship between the materials.
This paper details an experimental approach to determine if there could be such an effect, using a modified form of existing wood decay testing methods. The test utilises an agar jar approach with a pad of fibrous insulation e.g. wool or hemp placed between the inoculated agar and a wood block.
Results show the effects of eh type of insulation used on the moisture content and decay of the test blocks. The test show that wool for example appeared to hold water away from the wood samples and reduced subsequent decay. Hemp however, did not prevent water access to the wood blocks and in fact enhanced decay of the blocks.