Black Mould in Rented Properties: When Housing Disrepair and Respiratory Expert Evidence May Be Required

Black mould in a property is not simply a cosmetic concern. Persistent damp and mould may indicate underlying defects in the building, inadequate ventilation, water ingress, ineffective heating or other forms of housing disrepair. Where occupants develop respiratory symptoms, the issue may also become relevant to questions of medical causation and the extent to which housing conditions have affected their health.

For solicitors dealing with housing disrepair claims, obtaining appropriate expert evidence can therefore be important. A housing disrepair expert witness may assess the condition of the property, identify defects and consider whether remedial works are required. Where a claimant alleges that exposure to damp and mould has caused or exacerbated respiratory problems, a respiratory expert witness may be instructed to consider the medical evidence and provide an independent opinion on causation.

The Government’s current guidance on damp and mould in rented homes recognises that damp and mould primarily affect the airways and lungs and that the consequences can, in serious cases, be significant. It also emphasises that landlords should investigate the underlying causes rather than merely remove visible mould.

 

What Causes Black Mould in a Property?

Mould is a fungus that develops in moist environments. Although the term “black mould” is commonly used to describe dark-coloured mould growth, colour alone does not establish the species of mould present or determine its health effects.

There can be several causes of damp and mould in residential accommodation, including:

• Condensation caused by excessive moisture and inadequate ventilation.
• Penetrating damp arising from defects to roofs, walls, windows or external structures.
• Leaking pipes, plumbing defects or other sources of water ingress.
• Rising damp associated with problems affecting the structure or damp-proofing.
• Defective heating or ventilation systems.
• Inadequate insulation or low internal surface temperatures.
• Building defects that allow moisture to enter or remain within the property.

The Government’s damp and mould guidance specifically warns that there may be more than one cause of damp and mould and that simply cleaning or removing visible mould will not necessarily resolve the underlying problem. A proper investigation should therefore consider the source of moisture and the condition of the building as a whole.

This distinction can be particularly important in a housing disrepair claim. It may be insufficient to establish that mould is visible. The relevant question may also be why it has developed, whether the landlord knew or ought to have known about the underlying defect, and whether reasonable remedial measures were undertaken.

 

Can Black Mould Cause Respiratory Problems?

Damp and mould can affect the respiratory system because people are commonly exposed by breathing substances associated with mould and damp environments. The Government identifies respiratory effects including cough, wheezing and shortness of breath and notes that people with certain underlying conditions may be at increased risk.

This does not mean that every respiratory symptom experienced by a person living in a property with mould has necessarily been caused by the housing conditions. Establishing medical causation requires consideration of the individual circumstances, medical history, exposure and other potential causes.

This is where a respiratory physician expert witness may have an important role.

A respiratory expert can review the available medical records, history and relevant investigations and provide an independent opinion on issues such as:

• The nature and diagnosis of the respiratory condition.
• The symptoms reported by the claimant.
• The likely causes or contributing factors.
• Whether exposure to damp and mould is capable of causing or exacerbating the condition in question.
• Whether the timing of symptoms is consistent with the alleged exposure.
• The significance of pre-existing respiratory disease.
• Prognosis and likely future consequences, where relevant.

The expert’s role is not to assume that mould caused an illness simply because the two circumstances coexist. Rather, the expert should consider the available evidence objectively and explain the reasoning supporting any opinion on causation.

 

When Is a Housing Disrepair Expert Witness Required?

A housing disrepair expert witness may be appropriate where there is a dispute about the physical condition of a property or the cause and extent of alleged defects.

An expert assessment may consider matters including:

• The presence and extent of damp and mould.
• The likely source or sources of moisture.
• Building defects contributing to the problem.
• Ventilation, heating and insulation.
• The adequacy of previous repair works.
• Whether remedial works have addressed the underlying cause.
• The nature and extent of any continuing disrepair.
• The works reasonably required to remedy the defects.

An expert may also consider photographic evidence, repair records, inspection reports, correspondence, environmental information and other relevant documentation. Where appropriate, a physical inspection of the property can provide information that cannot reliably be obtained from photographs alone.

The Government’s guidance recommends inspection of the home to assess the presence, severity, location and underlying causes of damp and mould. It states that an assessment based solely on photographs may fail to identify the full extent of the problem.

This can make expert evidence particularly valuable where the parties disagree about whether the mould is the result of structural or building defects, condensation, lifestyle factors, or a combination of circumstances. ECR’s guide to building surveyor expert witnesses explains the wider role such experts can play in property-related disputes.

 

The Importance of Distinguishing Housing Evidence from Medical Evidence

Housing disrepair and medical causation are related but distinct questions.

A housing expert may be able to explain why mould developed, whether defects existed and what works were required. A respiratory expert, by contrast, addresses medical questions concerning the claimant’s health and the relationship between the alleged exposure and the medical condition.

Neither expert should be expected to stray beyond their professional competence.

For example, a building surveyor may identify persistent damp, defective ventilation and extensive mould growth, but that does not in itself establish that the claimant’s asthma or other respiratory condition was caused by the property.

Similarly, a respiratory physician may identify a plausible relationship between environmental exposure and respiratory symptoms, but will not ordinarily be the appropriate professional to determine whether defective guttering, inadequate damp-proofing or a failed ventilation system constitutes housing disrepair.

In appropriate cases, the two forms of evidence can therefore work together. The housing expert establishes the relevant environmental facts, while the respiratory expert considers the medical implications of those circumstances.

 

What Evidence Should Be Preserved?

Where black mould or damp is present, contemporaneous evidence can become important in any subsequent dispute.

Tenants and their representatives should consider retaining:

• Dated photographs and videos of affected areas.
• Correspondence reporting the problem to the landlord or housing provider.
• Repair requests and responses.
• Records of inspections and repair visits.
• Photographs showing the progression of the mould.
• Information concerning leaks, condensation or ventilation problems.
• Medical records relating to relevant respiratory symptoms.
• GP, hospital or specialist correspondence.
• Records of prescribed medication where relevant.
• Evidence concerning disruption to occupation or use of rooms.

The Government recommends photographing and documenting the location of mould before removal where practicable, while also emphasising that health protection should remain the priority.

A comprehensive chronology can also assist an expert by establishing when the defect was first reported, what action was taken and whether symptoms developed or changed during the relevant period.

 

Housing Disrepair, Damp and Mould: The Current Legal Position

There are several legal standards relevant to damp and mould in rented accommodation in England. The Government identifies the Housing Act 2004, Environmental Protection Act 1990, Homes (Fitness for Human Habitation) Act 2018, Landlord and Tenant Act 1985 and the Decent Homes Standard among the relevant frameworks.

The Housing Health and Safety Rating System is also relevant to the assessment of hazards within residential properties.

The position has developed further for social housing tenants through Awaab’s Law. Since 27 October 2025, Phase 1 requirements have applied to emergency hazards and significant damp and mould hazards in the social rented sector. Current Government guidance for social landlords states that significant damp and mould hazards must be investigated within 10 working days and made safe within five working days following the investigation.

Where a property cannot be made safe within the prescribed period, the guidance provides for suitable alternative accommodation in relevant circumstances. Further preventative works may also be required to ensure that the hazard does not return.

These requirements reinforce the importance of identifying the underlying cause of damp and mould rather than treating only its visible symptoms.

It should, however, be recognised that the precise legal position will depend upon the tenure, facts of the case, applicable legislation and procedural circumstances. Expert evidence should assist the court with matters within the expert’s specialist knowledge rather than determine questions of law.

 

When Might a Respiratory Expert Be Appropriate?

A respiratory expert witness may be particularly relevant where a claimant alleges that living in a damp or mould-affected property has caused, aggravated or materially contributed to a respiratory condition.

Examples may include claims involving:

• Asthma symptoms.
• Persistent cough or wheezing.
• Breathlessness.
• Recurrent respiratory infections.
• Exacerbation of an established respiratory disorder.
• Other conditions where environmental exposure is alleged to be clinically relevant.

The need for expert medical evidence should be considered on the individual facts. The existence of mould does not automatically establish medical causation, and a claimant’s symptoms may have several possible explanations.

An appropriately qualified respiratory expert can provide an impartial assessment of the medical evidence and explain the degree of support for the alleged causal relationship. This can assist the court in separating established medical evidence from assumption or correlation.

 

The Role of Expert Evidence in Housing Disrepair Litigation

Expert evidence should be proportionate, relevant and directed towards the issues that require specialist knowledge. In civil proceedings, expert evidence is subject to the requirements of Part 35 of the Civil Procedure Rules and the associated Practice Direction 35.

The expert’s overriding duty is to the court. An expert report should therefore be independent, objective and reasoned, with the expert distinguishing between matters of fact and professional opinion.

Expert Court Reports’ existing guidance on instructing expert witnesses similarly emphasises the importance of selecting an expert with appropriate expertise, providing clear instructions and ensuring that reports comply with the relevant procedural requirements.

In a housing disrepair matter involving black mould and alleged respiratory harm, early consideration of expert evidence can help solicitors identify precisely which issues require specialist opinion. Depending upon the circumstances, this may involve a housing expert, building surveyor, respiratory physician or a combination of experts.

 

Conclusion

Black mould in rented properties can raise both housing and medical issues. Persistent mould may be evidence of an underlying defect requiring investigation and remediation, while prolonged exposure to damp and mould may also be relevant to respiratory health.

A housing disrepair expert witness can assist in establishing the physical condition of the property, identifying potential causes of damp and mould and explaining the remedial works required. Where there is an allegation that those conditions have caused or exacerbated respiratory illness, a respiratory expert witness may provide separate medical evidence concerning diagnosis, causation and prognosis.

The Government’s current guidance makes clear that landlords should address damp and mould promptly and investigate its underlying causes rather than simply removing visible mould. For social housing in England, Awaab’s Law has also introduced specific requirements concerning significant damp and mould hazards.

For solicitors considering a housing disrepair claim, careful selection of appropriately qualified and independent experts can therefore provide valuable evidence on both the condition of the property and any alleged health consequences.