Mould growth in buildings

Abstract

Many studies around the world have reported that moisture-related problems in buildings (i.e., dampness) increase the risk of health effects such as respiratory symptoms, asthma and allergy in both adults and children. However, there is only limited knowledge about which agents in indoor air or dust cause the reported health effects. Biological pollutants such as moulds is one of the explanations that has been suggested. The principal objective of this PhD study has been to increase the knowledge about mould growth in buildings and possible links between mould growth and health effects in humans.

In this PhD study, moisture-acceptance criteria concerning mould growth have been developed for several building materials. In general it would seem that spruce and chipboard have a greater resistance to mould growth compared to plywood and gypsum. Wind-breaking materials based on wood-fibre and gypsum had an even greater resistance to mould growth compared to the other materials. As the RH increased, germination of the spores was faster, and the development and strength of the mould growth increased for all materials tested. The experiments also showed that an increase of 1% RH had a greater influence on the mould growth than an increase in temperature of 8 ºC when the RH was above 85%. Exposure of building materials to high temperatures (up to 60 ºC) decreases, or inhibits, mould growth. But when the temperature exposure is discontinued, growth continues as if nothing had happened.

In this study we have carried out a close examination of low-slope compact roofs as a possible “risk construction” with regard to mould growth. The drying-out potential and the risk of mould growth were examined in roofs exposed to large amounts of water. The results showed that the drying-out potential for the water-damaged roofs were higher than expected, and increased with substantially more ventilation. The observed mould growth was relatively small compared to what was expected. In conclusion, flat or low-slope compact roofs would seem to represent a more robust construction regarding the risk of mould growth than first expected.

In this study, data from two field investigations in Norwegian and Swedish houses concerning different building characteristics, indicators of a moisture damage and indoor relative humidity in accordance to the risk of mould growth have been analysed. The results given in this study show that moisture supply is not a constant value throughout the year, but is dependent on the outdoor temperature. According to our measurements, it would seem that the design curves given in EN ISO 13788 need to be modified if they are to be used in hygro-thermal analysis, both with regard to shape and deflection points, and with regard to the level of varied occupancy and room types. It was also found that the variation of RH and moisture supply generally followed the expected daily variation of moisture production due to the use of the house and the rooms. It was also found that the moisture supply, when calculated on an hourly basis, is highly sensitive to changes in the outdoor air water-vapour content during the day and week. As a general conclusion, therefore, measurements of indoor air humidity should be made on a long-term basis, i.e. minimum one week of measurements.

No link was found between water supply and rooms with registered mould growth. Neither were there any links between indicators of dampness and mould growth indoors (as indoor culturable mould spores). This shows that reliance on measurements of mould spores in the indoor air, whether there is a moisture problem in the building or not, is too unpredictable. Reported or observed data concerning water staining and measurements of indoor air humidity are also necessary to verify an indoor moisture problem.

In this study there was a link between a higher percentage share of houses with one or more moisture indicators and types of ventilation, types of foundation and building period. There were more cases of registered mould growth in houses with no ventilation / natural ventilation compared to houses with mechanical ventilation, and in houses with basement cellars compared to those with slab on ground. There was also a link between greater registered mould growth in older houses compared to newer ones. In a risk-reducing strategy it might be useful to improve the ventilation and carry out improvements to the foundations in order to avoid potential moisture damage.

Knowledge about which agent is causing the reported health problems in buildings with moisture-related problems is limited. In this study there was no link between mould-spore concentrations (CFU) in the children’s bedrooms and asthma/allergy among the children. Based on these results, there is no reason to carry out one-time air sampling of mould CFU in indoor air of homes in order to identify risk factors for asthma/allergy in children living in Scandinavian countries. These results might also indicate that there could be agents other than mould spores that are the cause of the health effects in damp buildings.