It is well known that organic materials may be susceptible to attack from a range of fungal organisms and any bio-based material used in locations where there is the possibility of microbiological activity must be expected to be able to withstand or prevent such attack. There are a wide range of test methods and standards in place to test susceptibility although most of these test individual components such as wood or panel material. A wide range of old and new bio-based materials and novel construction techniques are showing an increase in use in new building and in the restoration of old buildings. These materials need to be assessed against microbial activity to determine if they are suitable for use in a particular area. Standard wood decay test methods are widely known and would seem applicable to many of the materials being used – especially where wood based products are used. However, due to their structure certain testing problems can arise. This paper seeks to test a variety of building materials, including sheep’s wool, mineral wool, hemp, wood fibre, cellulose flakes and assess the suitability of the testing regime on these materials. The method selected was the wood panel testing method DD ENV 12038, with some modifications to measure the extent of fungal growth as well as decay. The results show that although there was significant growth of the fungi through test samples only the lignocellulosic materials showed any appreciable decay. It was also noted that for some of the samples the structure of the material e.g. very thick or particulate fill, made the test sub-optimal.