## 1 Introduction  
Although mould growth in buildings is not a new problem, research into the growth conditions of these fungi is still of high topicality and importance. The quite common and repeatedly observed mould growth problems in buildings suggest that more information and deeper knowledge is required for their prevention [1]. Some of the most frequent causes of mould growth in buildings are high humidity, cold surface temperatures, wet objects, water hazards, poor air quality, etc. [2]. Due to ubiquitous viable spores, mould growth is possible in all indoor environments. This makes the complete avoidance of them impossible; however, the amount can be significantly reduced by ensuring proper air ventilation and limiting exposure to potential mould contaminators [3]. Different mould species characteristic of the indoor environment are usually found in damp and water-damaged buildings, some of which dangerously pollute indoor air [4, 5, 6]. From a health point of view, visible mould growth is the main concern [7]. It is suggested that mycotoxins production responsible for adverse health effects in buildings occurs when water activity (a\({}_{\text{w}}\)) at the surface of the material exceeds 0.90. However, significant toxin synthesis does not begin until a\({}_{\text{w}}\) reaches 0.95 [8]. Mycotoxic effects in indoor air can be caused by toxicen fungal spores, their fragments and mycelium as well as products of moulds metabolisms. These toxic or harmful compounds cause the well-known immediate allergic reactions, respiratory infections and even serious illness [2, 8]. It is important to note that killing fungal organisms usually does not destroy their antigenic or toxic properties. This means that even the presence of dead fungi still remains a problem long after the favourable conditions of mould growth have been eliminated [9]. Another important aspect is discolourationcausing visible and irreversible damage to objects, which is especially important for the artefacts in heritage collections that cannot be replaced [9; 10; 11; 12]. These circumstances have increased the public awareness of the potential risks of mould, demanding higher indoor air quality as well as searching for supporting strategies to control mould growth in homes and public spaces. Mould growth requires proper nutrients, which are self-provided by enzymatic digestion of organic materials [13]. Due to its organic nature and hygroscopic properties, wood is highly susceptible to mould providing sufficient nutrients for spore germination and mycelium growth. Some wood species are more susceptible to mould growth than others. It is suggested that the main influencing factors are the amount and composition of wood extractives [14], differences in such physical parameters as wood moisture content as well as density between different wood species have only minor effect on mould resistance [15; 16]. Within the same wood species, higher level of antifungal and hydrophobic wood extractives are reported as the main contributors for the enhanced mould resistance of heartwood over sapwood [17; 18]. Furthermore, by analysing mould growth on various wood species, it is found that mould resistance has a positive correlation with the amount of antifungal extractives [14]. It was found that softwoods generally contained higher amounts of antifungal extractives, which resulted in higher resistance comparing to hardwoods. It has also been hypothesized that the larger content of hemicelluloses contributes to the higher mould resistance of softwoods over hardwoods [19]. On the other hand, the mould resistance of heat-treated wood is only slightly improved, despite the significantly reduced amount of hemicelluloses [20; 21]. However, this could be attributed to the mould growth enhancing factors such as the removal of all initial antifungal extractives and the increase in the amount of monosaccharides [20; 22].