FACTORS AFFECTING THE DEVELOPMENT OF BIODETERIORATION IN WOODEN CONSTRUCTIONS

Water leakages are the general cause of moisture stress exceeding the moisture tolerances of constructions. Moisture stress causes biodeteri oration (mould, rot and insect damage) in wooden constructions. The de gree of damage is affected by the severity and duration of moisture ex posure and temperature, together with the sensitivity of the wooden co nstruction to environmental stress. The growth of mould fungi on woode n materials depends mainly on the air humidity, temperature and the su rface quality of wood. Long term humidity conditions above a relative humidity (RH) of 80% are a risk for mould growth in pine and spruce sa pwood when the temperature is between +5-degrees-C and +50-degrees-C. Between -5-degrees-C and +5-degrees-C the growth of mould fungi is slo w, and possible only when the relative humidity is above 90%. High nut rient content of the surface can stimulate the mould growth. In fluctu ating humidity conditions, the severity and cumulative time of conditi ons suitable for mould growth are critical factors for the development of mould fungi in constructions. Humidity conditions must be above RH 95% (around the fibre saturation point of wood, wood moisture content about 25-30%) for the spore germination and mycelium activation of br own rot fungi. Under unsuitable conditions, fungi are inactive, but th ey can become active quickly under suitable conditions. The degree of decay in wood depends on the total time the decay organism is active. The natural durability of wood varies with the environmental condition s, wood characteristics (wood species, sapwood or heartwood, etc.) and the decay organisms. The service time of wooden materials can be exte nded by modification of the wood.