This photo shows the formation of black mould in the corner of a room. The preconditions for mould growth are sufficient moisture and nutrient. Mould may for example grow on wallpaper, wall paint, paper, and wood etc. Moist and warm condition with little or no ventilation provide the ideal environment. Mould growth may begin at a relative humidity of 70% or on wet substrates.
The cause of wet and moist conditions in buildings may be constructional defects or just insufficient ventilation by the building occupant. If a building is poorly insulated heat loss will cause cool interior wall surfaces especially at the corners of a room. When temperature falls below the dew point water will condense on a hard surface leading to mould growth. Poor ventilation will contribute to the process.
Black mould at a skirting board indicating a damp wall base.
Black mould growth behind a boiler.
Mould will form in living areas due to water damages. Pipe bursts, leaking heating pipes and similar failures will cause wet surfaces and lead to mould growth when the right nutrients are available.
White mould on an old wardrobe in the basement.
The basement floor was frequently flooded due to a defect storm water sewer. Extensive mould growth can be often detected by its odour when entering the basement.
White mould on furniture within a basement.