Breaking the Mould: Should landlords be doing more?

February 26, 2018

Sustainable Homes’ study, Breaking the Mould, is investigating the causes of damp and mould in UK homes.

The first phase of the study has now been completed, and showed clear links between the severity of mould and incidence of respiratory conditions. Some species of mould can be highly toxic, and disturbing while cleaning can sometimes be hazardous. The study also revealed that mould is most likely to occur in homes with higher occupant density, and in homes that are less well insulated. This suggests that landlords may need to have a greater duty of care when housing families in older homes with poorer insulation. Residents must be made more aware of the need for adequate ventilation.

The aim of this study was to improve understanding of how various factors interact to raise or lower the likelihood and severity of mould occurring. The resident is usually not best equipped to resolve all of these factors, so the knowledge learned should help inform landlords to make decisions on design, management, resident interaction and most crucially health and wellbeing.

Why are we undertaking this research?

Our homes have the potential to either enhance or diminish our wellbeing, so it is important that we understand what factors have what implications, and how we can make changes that enhance health and wellness.

Damp and mould in the home can have serious health implications for residents, by raising exposure to allergens, causing or aggravating respiratory conditions and creating ideal conditions for dust mites. It is also an extremely widespread issue: in this study 1 in 2 respondents reported the presence of mould in their homes. There was also a clear link between the amount of mould present, and the chance that a resident with a respiratory condition would be living there (see chart below).

Percentage of homes with at least one resident with a respiratory condition

A common approach for both social and private landlords is to place an onus of the responsibility on the resident, to clean it and to prevent it reoccurring. This research shows instead that landlords have much greater capacity than residents to tackle the issue. Indeed, of the three primary factors that give rise to mould, only one can be controlled by the resident, and all three have solutions that landlords can implement:

  • Density of occupation (the number of residents per m²) is the most important influence on mould risk. Residents are not able to change the size of their home or their family, but landlords can take into consideration the appropriate occupation density when housing residents.
  • Homes with poor or failed insulation give rise to cold spots on walls, to which condensation is attracted. This is also a factor outside residents’ control. Thermal imaging can be carried out to identify cold spots and then rectify insulation flaws.
  • Residents do not always link the importance of ventilation with their experience of condensation and mould. They are often much more concerned with keeping the heat in, than with a regular ventilation regime. Clear advice from landlords on good ventilation practice could help residents manage condensation and mould issues.

If landlords can quickly diagnose the cause of mould within each home and identify suitable remedies, they can potentially improve the health of an enormous number of residents. In addition they can optimise the quality, condition and suitability of their housing. Understanding the complex, interrelated factors causing damp and mould is an important first step for improving management.

Conditions for mould growth

Mould growth requires the following conditions:

  • Mould spores, which are found very commonly in the air
  • Moisture, particularly water vapour that has condensed onto a surface. This occurs when there is more vapour than the air is able to hold
  • An acidic environment
  • Nutrients, which may come from wallpaper or fabrics
  • Time – mould growth appears 6 hours to 10 days after suitable conditions occur
  • Temperature – the higher the temperature, the faster the mould growth


Of these conditions, the most difficult to control is the level of moisture in the air, since the more people live in a home, the more moisture there will be. Providing enough ventilation to clear it can sometimes be extremely challenging, so there is an increased risk of condensation.


Factors increasing the condensation risk



Human input Breathing, perspiration, bathing, clothes washing and cooking all release moisture, which raises humidity
Ventilation The presence or absence of mould is largely down the ability to remove moist air from the home fast enough, via ventilation
Airtightness This can cause a build-up of moisture if there is not sufficient ventilation
Failure of insulation Gaps in insulation, unsuitable materials and insufficient insulation can create ‘cold bridges’, where heat can pass from outside to inside more easily. Mould may occur in these cold spots


This infographic shows common issues in the home that can contribute to damp and mould:

Link between occupant density and mould severity

The higher the density of occupants in a home, the greater the severity of mould. This is because moisture levels rise faster, so higher ventilation rates are needed to avoid damp from occurring. This was the most significant factor contributing to higher mould severity.

Incidence of mould compared to occupant density and respiratory conditions


Link between energy efficiency and reduced severity of mould

The use of ‘Big Data’ analysis techniques enabled us to identify the relative importance of a range of different factors in their contribution to condensation. The top five most important factors leading to mould were as follows:

  1. The greater the occupant density (residents per m²) – the greater the risk of mould
  2. Better insulated homes, with a higher Energy Performance Certificate (EPC) score, had a lower mould risk
  3. Age of the home: the newer the home, the lower the mould risk
  4. Loft insulation: the more loft insulation, the lower the risk
  5. Occupants during the daytime: the more people at home during the day, the higher the risk


Next steps

Phase 2 of the study is underway at present (February 2018). This monitoring stage, combined with a final questionnaire will enable us to include  analysis of internal temperature and ventilation rates to the factors that contribute to mould risk.

We are very grateful for the participation of Basildon Council, Croydon Council, East Thames Ltd (part of L+Q Group) and Whitefriars Housing (part of WM Group).


Breaking the Mould is sponsored by

Bill Wright

Bill Wright