Surface moulds occur on external and internal surfaces of walls and partitions, frequently adjacent to ceilings, usually accompanied by persistent condensation or some other form of wetting. Moulds are unsightly and may also cause premature failure of paint films. As well as being unsightly, mould on internal surfaces is thought to cause respiratory problems in susceptible individuals; some forms of mould are actually toxic.
Mould problems and health
The moulds that grow in housing have long been associated with health problems; the most common are respiratory allergic reactions to mould spores and the faecal capsules of the dust mites that are associated with moulds. Spore concentrations in the air of buildings in which there is actively growing mould are much higher than where there is no indoor mould growth: here, the indoor air spore content is determined by that outdoors, causing great indoor variation day-to-day and seasonally. Indoor spore content ranges from 10% to 50% of that outdoors, and increases transiently with an increase in human activity, vacuum cleaning for example. Mould growth is less common in homes which have better insulation, cavity walls, good ventilation and air circulation, effective heating with no unflued combustion appliances and a generally good state of repair. It is therefore less common in newer homes.
Mould spores affect sensitive atopic individuals, the elderly and the very young, causing asthma, chronic or perennial rhinitis, conjunctivitis and eczema. About 80% of asthmatics in the UK are allergic to dust mites; data from the English House Condition Survey shows that families living in houses with mould are three times more likely to include an asthmatic than those in houses with no mould. There is increasing epidemiological evidence suggesting that moulds which commonly occur in dwellings are producers of potent mycotoxins, which exhibit toxicity to human lung cell linings and can have severe effects on the health of occupants.
More severe, sometimes fatal, illnesses, with names like ‘farmer’s lung’ or ‘maltster’s lung’ have been resulted from exposure to mould spores in the past; however, the evidence is that these are associated with mould species different from those found in housing and with spore concentrations many orders of magnitude higher. However concerns are now being expressed that severe health problems can be caused by a particular species of moulds, Stachybotrys Chartarum, that propagates and grows in the persistently wet conditions following from, for example, a burst pipe or leaking roof. Cases of this, which have led to significant compensation claims have been reported from the USA. This condition may be most important in buildings that have not been adequately dried out after flooding. There is no evidence that any comparable problems have arisen in the UK but, with flooding expected to become more frequent, it is worth watching for the occurrence of this fungus.