138 THE BUILDING CONSERVATION DIRECTORY 2025 CATHEDRAL COMMUNICATIONS DAMP, CONDENSATION and MOULD JOHN EDWARDS MANY PEOPLE believe that older buildings are more prone to moisture problems than newer ones, but if they look more closely, they would realise that problems are more usually caused by the ill-informed changes or treatments which have taken place. On too many occasions where damp is found, so called remedial work is undertaken without adequate investigation, only to see the problems reoccurring. This cycle then repeats itself over many decades. This has to stop for many obvious reasons, not least the waste of resources, the deterioration of the building and the damage it can cause to human health. Surveyors and contractors need to adopt certain principles in dealing with damp, condensation and mould, and also be sufficiently competent to investigate these issues properly. In addition, they must have a logical and consistent process to follow and be equipped with the most appropriate tools and equipment. Without these, any investigation will be flawed. The advent of Awaab’s Law in October 2025 will put in place very strict deadlines to deal with this problem in social housing in England. Named after Awaab Ishak, a two-year-old who died from a respiratory illness linked to damp and mould in his social housing property, the law requires social landlords to investigate damp, mould and condensation problems within 14 days of them being reported, and to commence remediation within a further seven days if they are found to pose a significant risk to health. This means that swift and appropriate action needs to be taken, based on a proper understanding of the problem and its causes. These requirements are likely to be extended to include the private rental sector and no doubt other UK home nation governments will follow suit. Working at pace to comply with Awaab’s Law means short timescales may increase the risk of misdiagnosis and inappropriate treatment. The risk has also increased with a lot of ill-informed retrofitting of traditionally constructed buildings, such as the insertion of many chemical damp courses. All of this must stop. THE PROBLEM WITH MOULD Mould is a biological growth made by some types of fungus to spread its spores. It is commonly seen as a dusty bloom on the surface of fruit or as black patches on the walls of poorly ventilated bathrooms, for example. The spores they spread contain chemical compounds known as secondary metabolites which help them to compete with other organisms in their ecological niche. (One of these fungal secondary metabolites was repurposed by Alexander Fleming and named penicillin because it is effective at killing other bacteria.) Unfortunately many of these secondary metabolites pose a health hazard to humans, particularly when the spores accumulate in the air of damp, poorly ventilated spaces. Inside a house, mould growth does not need condensation but it does require high levels of relative humidity (RH) and at around 90 per cent the process of germination can begin. If the RH per cent then stays at around 70 per cent this will be enough for mould to sustain itself, helped along with food which includes dirt and dust, hence the need to understand dust and debris accumulation. There are over 100,000 different types of moulds. We can help identify these by looking at their appearance and the most likely circumstances and location in which to find them. While some moulds might be of minor concern, without laboratory testing one cannot be absolutely certain about a specific mould type, and it is generally wise to be on the safe side. Moulds which are considered harmful to people1 are classified as follows (although some fall under more than one of these classifications): Allergenic – moulds which can trigger allergic reactions and asthma attacks in people who have allergies and cause slight allergy symptoms in those who don’t have allergies. Pathogenic – moulds which cause symptoms in people with immune system disorders or those with a serious illness or recovering from one. Toxigenic – moulds which can cause serious health issues, even in healthy people. These are the most dangerous ones. When examining mould in a building we should therefore understand that any mould is potentially dangerous, especially black mould. Mould can also change appearance as it develops which is another reason why it can be difficult to identify it just by appearance. There are many occasions where one can make a judgement on the type of mould but find it isn’t in the 1 Not all moulds are not harmful to humans (Penicillium for example) Black mould on the underside of a flat roof void. It has the features of Chaetomium but could it be something else? In reality, it’s black mould and should be considered a danger. (All photos: John Edwards)
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