Fungal damages in Norwegian massive timber elements – causes and measures
M S Austigard, J Mattsson
Massive wood elements are relatively new in Norway but the use is growing quickly, primarily the use of cross-laminated timber (CLT). Moisture performance of massive timber elements has been examined by some researchers, but more knowledge is needed. There is uncertainty regarding the need for vapour barriers or retarders in roof assemblies, and for practical reasons buildings are rarely assembled beneath construction tents despite awareness of the elements being moisture sensitive.
Eleven cases regarding massive timber from the Mycoteam database have been studied. The cases were evenly distributed between the construction phase and the use phase. The types and causes of damage have been compared, and remedial measures studied where possible. Examination showed challenging in many cases, and long electrodes inserted into pre-drilled holes was often found the most feasible method for moisture measurements. The construction had to be opened to allow examination in five cases. Drying was observed to take from one week to more than five months, depending on extent and duration of wetting as well as drying conditions.
The cause of moisture intrusion in all cases but one was insufficient protection from precipitation, either during the construction phase or due to construction errors such as faulty fittings or membranes. Fungal growth was observed in all but three cases, while decay was found in six cases. High moisture content within CLT elements did not cause fungal growth if the surfaces were kept dry. The major decaying agent in outdoor exposed CLT was Gloeophyllum sepiarium, whereas Antrodia sp. was most common in CLT not exposed to outdoor conditions. The authors expect the variation in decaying agents found in CLT not externally exposed to increase as the buildings age. More research is needed regarding risk of fungal damage in massive timber elements in combination with other materials.