Understanding dampness: from symptoms to sources

Poor housing conditions continue to pose a significant challenge across the UK. A 2021 Building Research Establishment (BRE) report found that 2.6m homes in England, around 11% of the national housing stock, were of poor quality.

The report suggested that this could be costing the NHS £1.4bn per year in patient treatment bills – a cost that rises exponentially when other services such as care in the community, health visitors and nursing care are factored in.

Among the most common and damaging defects is dampness, which the World Health Organisation identifies as a leading contributor to building envelope failure.

Yet despite its prevalence and deleterious effects, dampness remains one of the most misunderstood problems in the built environment. Misdiagnosis can result in ineffective remedial works, unnecessary costs and an overreliance on commercially driven solutions that fail to address the root cause.

This article series therefore advocates an independent and holistic pathological approach to determine the true causes of damp and mould in buildings, which often involves the invasive testing and monitoring of building elements and environmental conditions.

These methods have been incorporated into PAS 2035:2023 and BS 40104:2025. The findings and advice from these standards can be summarised as follows.

• Dampness investigations should be holistic, evidenced-based and undertaken by trained independent non-commercial practitioners who are qualified to carry out pathological building surveys.
• Wrong diagnosis leads to wrong remediation.
• Wrong remediation can destroy buildings, especially after the installation of external and internal wall insulation.
• Retrofitting must be evidence-based, ventilation-led and moisture-risk assessed.
• Inappropriate or unnecessary damp-proofing interventions can fail to resolve the moisture source and may, in some circumstances, exacerbate moisture retention or damage vulnerable building fabric.

While some housing maintenance professionals, national newspapers and others – including BSRIA's Mould in Social Housing and UK government guidance – argue that these conditions can be exacerbated by occupants under-heating and inadequately ventilating their homes, the Housing Ombudsman cautions against assuming occupant behaviour is the primary cause without a proper investigation.

So, who is to be believed?

The tragic death of two-year-old Awaab Ishak in December 2020, and the coroner's findings published following the inquest in November 2022, prompted significant regulatory and policy change in form of The Hazards in Social Housing (Prescribed Requirements) (England) Regulations 2025, commonly known as Awaab's Law.

This new legislation compels social landlords in England to respond promptly to tenant complaints of mould and damp within strict timeframes (see Table 1).

The Homes (Fitness for Human Habitation) Act 2018 introduced section 9A of the 1985 Act, which implies a new covenant into residential tenancy agreements in UK housing law and came into effect in October 2025.

While its initial focus is damp and mould, over the next two years it will be extended to cover the remaining Category 1 hazards under The Housing Health and Safety Rating System (England) Regulations 2005 (see Table 2).

As building surveys typically rely on observation and electrical resistance or capacitance moisture meters, surveyors can find themselves uncertain about the cause and source of dampness and mould.

Under the principle of caveat emptor (buyer beware), they may recommend further investigation where dampness is suspected but cannot be fully assessed within the scope of the survey.

The concern is not the referral itself, but the independence of the next-stage assessment. A conflict of interest may arise if the firm diagnosing the problem is also positioned to sell or install the remedial solution.

As a result, many properties receive expensive, unnecessary chemical damp-proof courses while the actual sources of moisture remain untouched, allowing damp and mould to return.

Such commercially driven diagnoses often leave dampness hidden in the home, which continues to hydrate the building's internal atmosphere, raising humidity and contributing to further mould outbreaks.

Of particular concern is where an older property has received both a retrofit chemical damp-proof course and retrofit external or internal wall insulation. Such practices can lead to serious levels of retained internal moisture and more rapid decay/deterioration of certain building elements, including timber, plaster and decorations.

The challenge in the built environment sector is that practitioners should be able to demonstrate appropriate competence, experience, professional indemnity cover and independence for the nature and complexity of the investigation.

Further training and regulation are needed to ensure there are sufficient building pathologists with the knowledge, skills and equipment to go beyond the identification of the symptoms and find the cause and source of the dampness.

This article concerns diagnostic building pathology investigations that may go beyond the scope of an RICS home survey and should not be confused with a statutory HHSRS assessment or PAS 2035 retrofit assessment. RICS' damp and mould consumer guide covers common sources of moisture, the impact on health and ways to deal with dampness. It offers advice for homeowners, tenants, landlords and managing agents, as well as case studies and helpful descriptions.