Healthy Homes: Mould in Buildings and Retrofit
According to WHO Housing Guidelines, healthy housing is a human right and a first call for disease prevention. This means that for the retrofit sector, understanding of the impact of mould in buildings is a requirement, not an option.
Damp patches, superficial as they may look, infect far more than the walls and ceilings they grown on. Mould significantly damages respiratory health, disrupts lives, and costs the economy billions worldwide. In 2020, prolonged black mould exposure caused the tragic death of two-year old Awaab Ishak and this has resulted in widespread regulatory changes to Landlord legislation in Scotland and the UK: Awaab’s Law.
For those delivering retrofit or involved in the refurbishment of homes, you have a crucial role to play in the mitigation of mould exposure. It’s critical to: 1. have awareness of the issue; 2. understand the way you can mitigate risk, on both a systemic and individual level.
Unhealthy homes, unhealthy people
Mould in our homes and work represents one of the most pressing social and health challenges facing the UK today, particularly in Scotland, where a high proportion of older housing stock combined with climate contributes to a persistent high risk of moisture.
This problem is frequently seen across the UK. Condensation, the most common cause of damp and mould in UK homes, is widely reported to affect around 1 in 5 households.
There also is strong evidence linking damp and mould to respiratory illness, infections, and poor indoor air quality (IAQ) and respiratory conditions are the fourth most common reason for sickness absence in the UK labour market.
What are the health effects of mould?
Exposure to mould is like breathing in a slow-acting toxin. While the immediate effects may seem minor to completely unnoticeable, the cumulative impact can permanently alter a person’s respiratory health and quality of life.
Research consistently shows that living in damp or mouldy environments is associated with a 30% to 50% increase in the risk of asthma. Certain groups are disproportionately affected. For instance, children living in mouldy homes have a significantly increased relative risk for both allergic and nonallergic respiratory diseases.
Why moisture matters in retrofit
In a recent Healthy Buildings Network seminar, Dr Sarah Price of Leeds Beckett University outlined why moisture remains the single biggest risk in domestic retrofit, drawing on academic research, national audit findings, and her work on PAS 2035.
Moisture in buildings is linked to around 80% of building failures. This moisture can take different forms, either as water vapour (humidity), liquid (rain penetration, leaks, rising damp), or even ice.
Mould thrives in environments with a relative humidity (RH) exceeding 60-70%. The optimal indoor relative humidity range for health and comfort is around 40–60%, which many UK homes exceed. Therefore, the impacts on humidity and identifying and mitigating water leaks should be key priorities in any refurbishment work.
A UK-specific health and housing case study
Data from major UK social housing retrofit programs, such as the Social Housing Decarbonisation Fund (SHDF), highlight the prevalence of these issues before intervention. Prior to structural improvements, 39% of UK residents in surveyed projects reported issues with mould or mildew in their homes. Significant percentages of UK residents faced conditions that foster mould growth, including 54% reporting draughts, 47% experiencing heavy condensation, and 46% struggling to heat their homes to a comfortable temperature.
Following fabric-first retrofits, 55% of residents agreed their homes had fewer issues with damp, mould, and condensation, and 33% reported a positive impact on their mental health.
Moisture in traditional vs modern construction
Building typology is a key distinction for dealing with moisture, in particular in UK retrofit sector which deals with buildings that could typically range from anywhere between 1 to 150 years old. Traditional buildings are often moisture-open: they absorb and release moisture, whereas modern buildings are typically moisture-closed, more likely to use insulation, vapour control layers and airtight systems.
Problems arise when modern, vapour-closed approaches are applied to traditional buildings and drying pathways are unintentionally blocked.
This is why a careful, building-specific approach and risk assessment, rather than “one-size-fits-all” solutions, must be used. Applying the wrong solution to the wrong building could mean that an upgrade, intended to make building healthier, better and more comfortable in fact makes it worse.
What can the retrofit and building community do?
Moisture is the critical, often underestimated risk in retrofit. Despite years of research and standards development (e.g. PAS 2035), the same mistakes are being repeated due to skills gaps, poor design integration, and systemic issues.
Sarah recommends some key points for tackling this. In her view, successful retrofit requires a whole-house, building-specific approach and a deep understanding of moisture behaviour, combined with appropriate materials for traditional buildings and effective ventilation. This should all be underpinned by stronger training, competence frameworks, and oversight.
Strategic recommendations
Systems thinking
Evaluating the interactions between different building components, such as insulation, heating, and ventilation, to ensure that energy-saving measures like airtightness do not inadvertently cause health issues like stagnant air or mould.Appropriate material choice
Different materials will be more appropriate for different building types. For example, recent modelling research also highlighted by Dr Price, examining moisture risk at joist ends in internal wall insulation retrofits, found wood fibre insulation to be lower risk than mineral wool or PIR.Proactive, preventative approach
Taking a proactive approach to reduce the risk of damp and mould - understanding the condition of a home and adopt a preventative approach to dealing with damp and mould, making the necessary interventions to ventilation, energy efficiency and building deficiencies before damp and mould occur.
Going forward
The solution to the UK's mould crisis requires rigorous application of existing knowledge, commitment to quality craftsmanship, and recognition that healthy housing represents both a human right and method for disease prevention.
The health of millions depends on the sector's willingness to embrace this challenge with the seriousness, skill and systemic thinking it demands.
For more information, the UK Government have guidance for registered social landlords on understanding and addressing the health risks of damp and mould in the home.