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Water damage and mould growth in buildings

Apr 8, 2024

Jagjit Singh 

Managing Director, Environmental Building Solutions, UK 

Jagjit Singh, BSc MSc PhD CBiol MIBiol FIRTS FRSH FRSA, building mycologist and pathologist, is a director of Environmental Building Solutions Ltd.  He specialises in building health problems, heritage conservation and environmental issues and has more than 35 years’ hands-on experience in surveying historic buildings.  Jagjit has carried out environmental surveys for dry rot, wet rot, moisture, damp and decay, moulds, environmental health surveys, monitoring of historic buildings and provided recommendations for environmental control.  EBS’s reputation is for non-intrusive investigations for insect and fungal attack including dry rot, wet rot, timber decay, damp, hazardous materials surveys, heritage building investigations and the development of innovative techniques including recommendations for environmental management sympathetic to the building fabric finishes and components, notably the avoidance of chemicals and cementitious tanking materials, This approach is well respected by conservation and heritage authorities.  

Jagjit has published in excess of 250 technical papers and communications, contributed to books and lectured widely on care and conservation of collections, building pathology and building health problems, covering wide areas such as fungal infestation and environmental control, timber decay in buildings, damp and decay in buildings and drying out buildings after fire and water damage, environmental monitoring and control of moisture, mould and biological contaminants, indoor air quality and health implications in buildings. Jagjit has edited several books including Building MycologyManagement of Decay and Health in BuildingsEnvironmental Preservation of Timber in BuildingsAllergy Problems in Buildings and Environmental Monitoring of our Cultural Heritage: Sustainable Conservation Solutions. He is a BBC expert and has appeared twice in the Raising the Roof series. He is an ex-president of the International Society for the Built Environment (ISBE). 


This paper is about water damage in buildings and the resulting mould infestation, its causes, detection, identification, remediation and health Implications. The author believes based on science, practical experience and successful case studies over the last 37 years that by proper understanding of the causes, much misdiagnosis, misidentification and mistreatment can be avoided, and correct testing, identification and enumeration of the moulds is the vital key to successful remediation measures. All moulds are not equally destructive, toxic or pathogenic. It is important to determine the type and extent of both visible and non-visible mould and hidden moulds in floor voids, wall voids and other con- fined spaces. 

Keywords: water damage and mould, causes of mould, moulds and health Implications, detection of mould, hidden moulds, mould remediation 

Jagjit Singh 



Building mycology is defined as that branch of mycology dealing with the study of fungi in and around the building environment.1 

After natural disasters such as floods, excess moisture, standing and stagnant water may contribute to the growth of mould and other microbial contaminants in homes and other buildings. Sewage contamination also increases these risks. When returning to a home that has been flooded, it is very likely that mould will be present and may be a health risk for its occupants. Similar issues may arise after fire damage. 

Fungi are ubiquitous and there is almost no habitat that they cannot colonise. Fungi may enter buildings from outside, but the most important sources are usually within buildings. For example, organic dusts, rich in microorganisms, can originate from many different materials in buildings. 

There are estimated to be over 3m fungal species, although only around 150,000 fungal species have been described to date and only approximately 80 genera are known to cause illness. As the later section on health implications makes clear, however, persistent dampness and mould are associated with numerous health risks, and there has been increased awareness of this due to recent litigation in Europe, USA and Canada, along with numerous reports of ‘toxic moulds’ in the national papers and media. Fungus-related issues following water damage in buildings have resulted in multimillion-dollar lawsuits and have caused serious problems for homeowners, facility managers and insurance companies, who must deal with the human issues and mould remediation.2 

Two species of fungus are of particular concern, as they are pathogenic in distinct ways: Aspergillus fumigatus is a fungal pathogen, and Stachybotrys chartarum (often referred to as toxic mould) produces mycotoxins and other biologically active compounds that are of concern to human health.  According to the World Health Organization (WHO) report ‘Indoor Air Quality: Biological Contaminants’,3 ‘the presence of certain fungal pathogens such as Aspergillus fumigatus and certain toxigenic fungi such as Stachybotrys chartarum should be considered unacceptable’. Therefore, it is of particular importance to undertake a range of sampling and tests to establish or rule out the presence of these moulds. For this reason, this paper places particular weight on S. chartarum, as saturation of building fabric following water damage most likely leads to the development of this fungus. 

There are many unanswered questions about the effects of S. chartarum on human health; however, research to date clearly demonstrates that one should not handle materials contaminated with S. chartarum without proper personal protection equipment (PPE) and safety procedures, and strongly indicates that indoor environments contaminated with S. chartarum are not healthy, especially for children, immuno- compromised patients or those with lung problems, which would put them at risk of opportunistic lung infections from indoor moulds and may result in serious illness. 

As a practising building mycologist, I have advised on issues concerning indoor moulds, their causation, detection, remediation and health implications following fire and flood damage to owners, estate managers, loss adjusters, general public, private institutions and insurance companies for over 37 years.


Buildings that suffer from water damage, residual moisture, chronic dampness, condensation, high levels of humidity and inadequate ventilation or malfunction of the building services/heating, ventilation and air conditioning (HVAC) systems provide favourable environmental conditions for the growth and proliferation of a variety of moulds (see Figure 1).4 

Figure 1: Water damage and resulting plaster fungal growth (Peziza spp.) and black mould 


Moulds spores are ubiquitous and will always be present indoors, partially from outdoor sources and partially from indoor reservoirs. The spores of S. chartarum are in the soil and can be introduced into the building along with flood waters or the dust and dirt entering with the water incursion.

Excess moisture on almost all indoor materials, contents, collections, artefacts and architectural decorative surfaces leads to growth of mould, fungi and bacteria, which subsequently emit spores, cells, fragments and volatile organic compounds into indoor air. Moreover, dampness initiates chemical or biological degradation of materials, which also pollutes indoor air. 

It is vital to understand that once mould growth has started in the building, each mould colony produces millions of microscopic spores within a few days. Moulds will grow if the relative humidity in the indoor environment reaches 70 per cent or above. Favourable microclimates, ecological niches and habitats include damp, dark places (e.g. cellars, bathrooms, garages, unventilated damp cavities and voids); rotting leaves, fruit, bread or vegetation, indoor plants and organic plant containers (e.g. wicker, straw, hemp), damp wallpaper and furniture. 

Mould growth and development initiate from spores in the presence of dampness and moisture; when the spore absorbs water, the cell wall expands to initiate growth through formation of hyphae and mycelium, similar to germinating plant seeds. 

Following fire and flood damage in buildings, the building fabric, materials, contents, fixtures and finishes become saturated, which provides favourable environmental conditions for mould growth and proliferation.  In particular, saturated gypsum-based plasterboard provides the ideal environment and nutrients for S. chartarum growth and proliferation. It should be noted that relative humidity of over 95 per cent is required to initiate and maintain S. chartarum growth. 

New regulations and codes for traditional structures, including energy performance certificate (EPC) requirements in particular, emphasise sealing historic buildings. Sealing these structures risks problems associated with excessive damp and humidity. Substantial renovation following water damage or a change of use, however, may cause an existing building to become subject to building regu- lations (Approved Documents L1B and L2B, concerning conservation of fuel and power in existing dwellings and buildings). 

Mould growth starts within 48 hours (see Figure 2) following water damage in buildings, and within a week extensive mould infestation and colonisation is visible. Particularly on saturated plasterboard, S. chartarum produces extensive fruiting structures (conidiophores and conidia) and within a week this gives the substrate a shiny black appearance and powdery appearance when the water dries out dry. 

Figure 2: Black mould on wall 



As the preceding section implies, some level of mould infestation is inevitable following water damage. To prevent extensive mould growth by a range of fungi including S. chartarum on building fabric, materials, finishes, carpets, cavities and voids and the resulting potential health implications, urgent, immediate actions are necessary. 

Urgent measures should be put in place to rectify moisture problems and correct understanding of the moisture distribution, moisture profiles and moisture sources, moisture reservoirs and moisture sinks in the water-damaged property. As soon as safe and practical, steps should be taken to halt further water ingress and establish passive ventilation, which may help to minimise secondary infestation. All water-saturated floor coverings, carpets, underlay, etc must be removed to encourage ventilation into cavities and voids. 

Damp and residual moisture tests, correct mould identification tests, fabric decay and deterioration tests must be undertaken on building fabric, materials, insulation and contents in order to ascertain whether walls, ceilings and timber elements can remain or should be exposed. Non-destructive testing of cavities and voids, including floor voids, wall voids and ceiling voids, should be undertaken in order to establish hidden reservoirs of fungal growth and spores. 

Any exposure works/removal works must be undertaken with engineering control in place to prevent recontamination from one space to another. 5 Mould-contaminated fittings, curtains, contents and possessions should be either discarded or decontaminated and stored away from the premises based on merit. Ensure appropriate PPE for operators and all those persons exposed to mould-contaminated environments. 

COMMON FUNGI AND ENVIRONMENTAL INFLUENCES Among the mould species isolated in water damage, damp and moisture-saturated buildings, the most common and dominant genera which I have encountered in my investigations over the last 37 years are the following: 

  • Aspergillus spp. 
  • Cladosporium spp.
  • Chaetomium spp., 
  • Penicillium spp.; and 
  • Stachybotrys spp. 


The most dominant species isolated are the following: 

• Alternaria alternata;
• Aureobasidium pullulans;
• Cladosporium herbarum, C. cladosporioides, 

c. sphaerospermum;
• Chaetomium globosum;
• Aspergillus versicolor, Aspergillus niger, 

Aspergillus restrictus, Aspergillus glaucus
• Mucor spp.;
• Rhizopus stolonifera;
• Penicillium expansum, Penicillium chry- 

sogenum, Penicillium brevicompactum, 

Penicillium spp. 1;
• Toxic Mould (Stachybotrys chartarum); • Trichoderma viride;
• Acremonium spp.;
• Aureobasidium spp.;
• Fusarium spp.;
• Yeasts and fungal hyphal fragments

The number and type of microorganisms change with time of day, weather, season, geographical location and with the presence of local spore sources. Under normal conditions in buildings, the building materials, substrates and contents do not allow mould growth; however, this occurs due to a range of building defects or fire and flood damage, which create conducive environmental conditions for growth and proliferation. 

Most moulds require dust, dirt and cellulose from, for example, Gyproc plasterboard lining, timber elements or wallpaper in buildings. Vegetative hyphae of most fungi grow at optimum temperatures 18–32°C, and, although most become dormant at sub- freezing temperatures, a few may sporulate below 0°C. At the other extreme, although 71°C is generally lethal for moulds, certain types thrive at slightly cooler temperatures. Aspergillus fumigatus and Aspergillus niger tolerate a wide range of temperatures. 

Environmental conditions such as relative humidity and moisture affect not only the growth and fruiting of mould but also the dispersion of spores and resultant prevalence in the environment. In the outdoor environments the mould spore counts typically rise 

with rainfall and fog and with damp nocturnal conditions. Rain and dew splash also foster dispersion of slime spores. As a result, atmospheric recoveries of FusariumPhomaCephalosporium and Trichoderma species peak with rainfall. 

The reproductive units of many fungi are detached by direct wind scouring or wind-induced substrate motion. Such dry spore dispersal increases as airspeed rises and relative humidity falls, peaking often during summer afternoons. At such time, typical spores of CladosporiumAlternariaEpicoccumHelminthosporiumRhizopusAspergillus and Penicillium species may also peak. Therefore, it is important to take air samples and particulate samples outside the building to set a benchmark for the outdoor environment, so that the indoor levels can be compared; if the levels inside are much higher than outside, then it is assumed that this is due to indoor sources. 


Detection of moulds in the indoor environment is usually by visual inspection, air sampling, particulate sampling and surface sampling. 

The fruiting structure (conidia) of S. chartarum are covered with slime residue, and thus remain on the conidiophore as a mass or ball of spores; therefore, the spores are not readily disseminated in the air and for this reason Stachybotrys is not isolated during routine air sampling compared to a range of other fungi such as Cladosporium, Aspergillus and Penicillium. However, when the Stachybotrys fruiting structure and substrate dries out or the contaminated building material is disturbed — for example, by removal of plasterboard or by mechanical means or air movement — conidia can become bioaerosols. Similar considerations apply to Chaetomium spp., also commonly found mould following water damage in buildings. 

Hence the detection of S. chartarum and Chaetomium spp. requires expert investigations. Because these moulds are not readily airborne compared to other fungi, air sampling in a contaminated indoor environment may show no or low levels of spores in the air. Contact sampling and material sampling is a reliable method of sampling S. chartarum infestation in buildings. Most of the commonly used media for mould evaluation in the indoor environment air are not adequate for growth of S. chartarum

Inspection of potential sites of contamination, especially hidden or covered and protected, is necessary to determine where the fungus occurs and the level of contamination. For Aspergillus fumigatus, allow for petri dishes incubation at higher temperatures eg 30–37°C for 5–10 days with periodic checking. If areas contaminated with S. chartarum and Aspergillus fumigatus are discovered, it is advisable to follow recommended health and safety procedures for working with moulds, especially if heavily contaminated environments. 

It is important to carry out a range of tests for mould contamination in water- damaged buildings. The tests should include air sampling for visible mould spores, particulate sampling for visible and non-visible mould spores and surface, and materials sampling, including sampling cavities and voids and exterior sampling for benchmark comparison. 

Assessment of exposure to moulds has traditionally relied on spore counts and microscopic identification and mould culture (indoors, in dust and air samples). More recently, enzyme immunoassays using poly- clonal antibodies have been developed to measure total antigen load in dust samples. Monoclonal immunoassays have been developed for specific allergens such as Alt a 1 and Asp f 1. Generic tests for b-glucans, ergosterol and extracellular polysaccharides have also been used to assess exposure to moulds.6,7 


During my investigations of health issues in buildings, mould infestation in buildings is not always readily visible to the naked eye, and often there are no visible signs on surfaces as the mould growth is hidden in concealed cavities and voids. Mouldy, musty, champagne or rubbery smells are good indications of extensive mould growth and contamination, however, because the smell indicates actively growing moulds producing volatile organic compounds, which escape into the indoor environment. 

The mould attack can be hidden in the saturated cavities and voids, ie ceiling voids, wall voids and floor voids with no or little visible evidence within the interior surfaces of the room. The mould spores’ dissemination from within the voids can contaminate the indoor environment of the room, as 

the size of a typical fungus spore is only thousandths of an inch and it can easily pass through crevices and cracks in the building structure, materials and finishes (see Figures 3, 4 and 5). 

Figure 3: Air sampling in concealed voids 


Figure 4: Contact sampling of mould infestation 


Figure 5: Active fungal infestation to Gyproc plasterboard 


Fibre optic inspection (borescope) of the concealed cavities and voids can reveal hidden mould attacks and air in the voids can then be sampled through these borescope holes to quantify mould contamination (see Figure 6).8–10 


The disturbance of mould-contaminated building materials, e.g. during refurbishment, renovation or demolition works, will generate airborne mould and the dust created by such activities can increase exposure to the moulds and their metabolites. Therefore, 

prior to any disturbance of these contaminated building materials and structures, preventative measures need to be put in place for health and safety. For example, it is advisable to apply some form of sealant to encapsulate the spores before removal from the building. Where major demolition works are to be undertaken, it is recommended to establish benchmark airborne levels of Aspergillus and continue to monitor during demolition works in order to detect any high-level airborne counts (colony- forming units per m3), which will require robust additional mitigation and preventative measures. 

Contaminated building materials and sur- faces should be coated with some form of sealant, such as wood glue, and then be dis- posed of in plastic bags to minimise handling of contaminated materials. Engineering controls such as barriers and negative pressure are recommended in severely contaminated environments (see Figure 7) to ventilate the working area with air from outside and to prevent contaminated mould dust entering into non-contaminated areas of the building. Disinfecting the surfaces of contaminated materials with bleach may kill the mould on the surface, but fungal hyphae and mycelium within the substrate will often survive and grow again. Therefore, removing contaminated materials is the best option, as mycotoxins may accumulate in contaminated material over time. 

It is important to carry out environmental remediation of moulds in the indoor environment and HEPA filter vacuuming all surfaces and contents and fogging cavities and voids to reduce the mould colony- forming units per m3. 

Following the completion of mould remediation works, it is important to reassess the cleanliness of the area and hence any possible ongoing exposure of the occupants. The use of air and surface sampling tests, with appropriate analysis, will allow a judgment to be made. Ongoing monitoring of the situation 

is vital to confirm that any structural repairs have been effective and that satisfactory drying out of the building is occurring. Of course, it is possible that the mould may return, and this is an issue that may need further consideration in due course. 


Dampness and moulds have been suggested to be a strong, consistent indicator of risk of asthma and respiratory symptoms (eg coughing and wheezing). The health risks of biological contaminants of indoor air could thus be addressed by considering dampness as the risk indicator.11 

Moulds are associated with diverse health effects, including allergic respiratory disease, infection (e.g. invasive aspergillosis), chronic sinus and pulmonary diseases, as well as more idiosyncratic diseases, such as chronic fatigue syndrome, lethargy, migraines, etc. Many different mould species have been implicated in disease causality and this, in combination with the diverse array of potential health effects, has made it difficult to establish clear relationships between mould exposure and disease activity.12,13 

Individuals with asthma, allergies or other respiratory conditions may be more sensitive to mould. Persons with immune suppression (such as people with human immunodeficiency virus [HIV] infection, cancer patients taking chemotherapy, patients on immunosuppressive medications and people who have received an organ transplant) are more susceptible to fungal infections.14 Therefore, if the persons exposed are allergic to mould or have asthma, being exposed to mould may make the condition worse. Persons suffering from chronic lung condition or a weakened immune system could develop fungal infections in their lungs, and they should try to avoid mould contaminated buildings. Even in healthy individuals or persons who do not have underlying allergies or lung problems, exposure to mould can result in respiratory symptoms and lung conditions. 

There is a comprehensive review of the scientific evidence on building deterioration and health problems associated with building moisture, moulds and other biological agents. The most important effects are increased prevalence of respiratory symptoms, allergies and asthma as well as perturbation of the immunological system. WHO’s published guidelines for protecting public health and for avoiding adverse health effects stress the prevention or minimising of persistent dampness and microbial growth on interior surfaces and in building structures.15–17 

Microbial growth may result in greater numbers of spores, cell fragments, allergens, mycotoxins (toxic by-products of mould growth), endotoxins, β-glucans and volatile organic compounds (VOCs) in indoor air. The causative agents of adverse health effects have not been identified conclusively, but an excess level of any of these agents in the indoor environment is a potential health hazard.18 

WHO19 and the Institute of Medicine20 review of the epidemiological evidence con- clude that there is sufficient evidence of an association between indoor dampness-related factors and a wide range of respiratory health effects, including asthma development, asthma exacerbation, current asthma, respiratory infections, upper respiratory tract symptoms, cough, wheeze and dyspnoea. There is clinical evidence that exposure to mould and other dampness-related microbial agents increases the risks of rare conditions, such as hypersensitivity pneumonitis, allergic alveolitis, chronic rhinosinusitis and allergic fungal sinusitis.21–24 

Fungi produce large numbers of spores, which can become attached to dust on building surfaces in the indoor air and can then be inhaled by occupants and deposited on the mucosal surface of the upper airways and in the eyes. Repeated exposure to large amount of fungal material risks the development of specific allergic reactions. 

Extrinsic allergic alveolitis (EAA) encompasses a broad spectrum of pulmonary interstitial and alveolar diseases caused by repeated (occupational) exposure to a wide variety of organic dusts, moulds, microbes and chemicals. Repeated expo- sure to various moulds can cause EAA. 

Mould-induced EAA includes wood pulp worker’s lung (Alternaria species), malt worker’s lung (Aspergillus clavatus), farmer’s lung (A. fumigatus), maple bark stripper’s lung (Cryptostroma corticale) and sewage worker’s lung (Cephalosporium species). 

Long-term exposure to mould and the development of mould allergies, such as allergic rhinitis, is prevalent in all age groups; typical symptoms of allergic rhinitis include runny nose, itchy nose, sneezing, nasal con- gestion, sniffling, sore throat, cough, itchy eyes and runny eyes. 

Mould allergies are usually caused by repeated exposures to damp and moulds and the immune responses of susceptible individuals. 

 Figure 6: Borescope Inspection of cavities and voids 


Figure 7: Extensive mould infestation 



  1. (1)  Singh, J. (1994), Building Mycology – Management of Decay and Health: An Integrated Approach, E & FN Spon, London. 
  2. (2)  Singh, J. (2020), ‘Moulds and health implications: Building risk assessment in a litigious age’, Journal of Building Survey, Appraisal & Valuation, Vol. 9, No. 3,
    pp. 1–14. 
  3. (3)  World Health Organization (WHO) (1988), ‘Indoor air quality: Biological contaminants’, available at https://iris. 9789289011228-eng.pdf?isAllowed=y.%20 Accessed%207%20Sept%20 2021.&sequence%20=%203 (accessed 25th September, 2023). 
  4. (4)  Singh, J. (June 2022), ‘Moulds in historic buildings’, Context, Vol. 172, pp. 45–46. 
  5. (5)  CIBSE (1999), ‘Minimising pollution at 

air intakes’, CIBSE Tech. Memo TM21, available at knowledge-research/knowledge-portal/ tm21-minimising-pollution-at-air-intakes (accessed 25th September, 2023). 

  1. (6)  Flanningan, B. (1992), ‘Indoor Microbiological Pollutants – Sources, Species, Characterisation an Evaluation’, in Knoppel, H. and Wolkoff, P., (eds), Chemical, Microbiological, Health and Comfort 


Page 331 

Water damage and mould growth in buildings 

Aspects of Indoor Air Quality – State Of The Art In SBS, Kluwer, Dordrecht, pp. 73–98. 

  1. (7)  Gravesen, S., Frisvad, J. C. and Miller, J. D. (1992), ‘Fungi as contaminants in indoor air’, Atmospheric Environment. Part A. General Topics, Vol. 26, No. 12, pp. 2163–2172. 
  2. (8)  Singh, J. (1991), ‘New advances in identification of fungal damage in buildings’, Mycologist, Vol. 5, No. 3, pp. 139–140. 
  3. (9)  Singh, J. (1993), ‘Biological contaminants in the built environment and their health implications’, Building Research Information, Vol. 21, No. 4, pp. 216–224. 
  4. (10)  Singh, J. (1994), ‘Indoor air quality in buildings’, Office Health and Safety Briefing, Crona. 
  5. (11)  World Health Organization (WHO) (2009), ‘Guidelines for indoor air quality: Dampness and mould,’ available at dle/10665/164348/9789289041683 -eng.pdf?sequence=1 (accessed 25th September, 2023). 
  6. (12)  Singh, J. (1996), ‘Impact of Indoor Air Pollution on Health, Comfort and Productivity of the Occupants’, Aerobiologia, Vol. 12, pp. 121–127. 
  7. (13)  Singh, J., Yu, C. W. F. and Kim, J. T. (2010), ‘Building Pathology, Investigation of Sick Buildings —Toxic Moulds’, Indoor 

and Built Environment, Vol. 19, No. 1, 

pp. 40–47.
(14) Gravesen et al., ref. 7 above.
(15) World Health Organization (WHO) 

(2009), ‘Damp and mould health risks, prevention and remedial actions’, available at https://intranet.euro.who. int/__data/assets/pdf_file/0003/78636/ Damp_Mould_Brochure.pdf (accessed 25th September, 2023); World Health Organization (WHO), ref. 11 above. 

(16) Institute of Medicine (US) Committee
on Damp Indoor Spaces and Health (2004), ‘Damp Indoor Spaces and Health’, Washington, DC. 

(17) World Health Organization (WHO), ref. 15 above. 

(18) Ibid.
(19) Ibid.
(20) Institute of Medicine (US) Committee on 

Damp Indoor Spaces and Health, ref. 16 

(21) Health Canada (1987), ‘Exposure 

Guidelines for Residential Indoor Air Quality’, available at https://publications. 156E.pdf (accessed 25th September, 2023). 

(22) Singh et al., ref, 13 above.
(23) World Health Organization (WHO), 

ref. 15 above.
(24) Singh, J. (November–December 2019), 

‘Spore Law’, Built Environment Journal, pp. 48–52. 

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