The Role of Transient Wetting on Mould Growth on Wooden Claddings

Abstract

Mold growth on the surface of wooden façades is usually dealt with by using surface treatment such as paint with fungicides. However, new developments in architecture are moving towards less use of coating, and more use of untreated wooden claddings. Mould growth is well understood and described, and several models for predicting mould growth on building materials exist. It is commonly known that mould growth is directly controlled by the climate which the wood is exposed to. Several authors identify humidity, temperature and time as the main drivers of mould growth. However, most of the current growth models developed are based on laboratory measurements at stable climatic conditions. Consequently, these models are less suitable for prediction of mould growth on exterior surfaces exposed to rapidly changing weather conditions. This paper analyses the effect of variations of meteorological data on the mould growth on wooden claddings. An experimental setup of wood samples was exposed to outdoor conditions and hourly weather conditions as well as the mould growth at different intervals were measured. The measurements were supplied with 1-D Heat And Moisture (HAM) simulations to provide a more accurate estimate of the conditions on the surface of the samples. The purpose of the analysis was to evaluate if an existing mould growth model might be applicable also for predicting outdoor mould growth. Several profiles of temperature and moisture were continuously monitored on different locations of an eight-story building made from Cross Laminated Timber (CLT). The results from the analysis of the samples of wood cladding were used to model the mould growth on different locations of the building. Also the drying effect of wind around the building was studied. The study shows that there is large variation of potential mould growth on the façade of the building.