Damp and mould in survey reports: why “mentioning it” is no longer enough

Most survey failures do not arise because a defect was missed entirely. They arise because something was seen, but not properly explained.

Damp and mould are a classic example. Many reports still include a brief line along the lines of “mould noted to bedroom wall – clean and improve ventilation”. From a distance, that can feel adequate. In practice, it often isn’t — and increasingly, it isn’t defensible.

The problem is not that the mould was overlooked. It is that the survey failed to explain why it matters, what it indicates, and what may happen if it is ignored. In today’s regulatory and legal climate, that gap is becoming harder to justify.

The context has changed — whether we like it or not.

The Building Safety Act 2022 sits within a wider shift towards accountability, competence and risk-based decision-making in the built environment. While the Act is primarily focused on higher-risk buildings and life-safety themes such as fire and structural risk, the emphasis on competent judgement and foreseeable risk aligns with expectations increasingly applied across housing work more generally.

Surveyors cannot reasonably argue ignorance where a risk is well established, routinely encountered, and preventable. Damp and mould fall squarely into that category.

The expectation is no longer just “did you see it?” but “did you understand it, contextualise it, and advise proportionately?” Simply noting that mould exists, without meaningful interpretation, leaves too much unsaid — and places the surveyor in a weak position if outcomes later escalate.

“It’s only mould” — a mindset that no longer holds

A phrase still heard too often in practice is: “It’s only mould — the client can wipe it off.”

That mindset is not supported by building science, by the health evidence base, or by how mould behaves in occupied dwellings.

Mould is not a decorative defect. It is a symptom of moisture imbalance. Where moisture persists, mould recurrence is predictable. Where recurrence is predictable, risk is foreseeable.

Treating mould as a superficial cleanliness issue encourages cosmetic responses and repeated failure. From a reporting perspective, it also leads to vague advice that does not stand up to scrutiny.

Minimum reporting standard (what “good” looks like)

If you want a defensible mould narrative without overreaching, your report should usually cover four basics:

• What you saw and where: location, extent, and whether staining looks historic or active.
• What it most likely indicates: the probable moisture mechanism  (condensation risk vs leak/penetration vs plumbing/service route vs air-leakage pathway).
• What happens if conditions persist: recurrence is foreseeable; risk of spread, fabric deterioration, and ongoing indoor air quality concerns increases.
• What next step is proportionate: action that addresses causes (ventilation/heating/fabric repairs), plus targeted investigation where the pattern justifies it, and clear signposting where it moves beyond survey scope.

This is not about writing an essay. It’s about making sure the client understands why it matters and what to do next, and that your reasoning is clear if the report is ever scrutinised.

Where surveyors should actually be looking

One of the most common weaknesses in mould reporting is over-reliance on what happens to be visible at the time of inspection.

Effective inspection goes wider than that.

Surveyors should be actively alert to mould and moisture risk in:

• cold external wall corners and window reveals, particularly in bedrooms and north-facing rooms
• behind furniture, wardrobes and beds where airflow is restricted
• ceiling edges, wall–ceiling junctions and poorly insulated lintels
• bathrooms, kitchens and utility areas — not just at silicone seals, but on surrounding finishes
• areas with recent redecoration that may conceal prior staining
• rooms that appear under-heated or poorly ventilated
• properties with retrofit insulation or airtightness upgrades without visible ventilation improvement

The absence of noticeable surface mould does not mean there is no risk. Historic staining, patchy redecoration, or faint discolouration can all indicate moisture conditions that remain active or readily recur.

Warning signs that matter more than colour

Many surveyors are understandably cautious about commenting beyond what they can “prove”. This can lead to an over-focus on colour as a comfort blanket — if it’s black, it’s mould; if it isn’t, we hedge.

That approach misses the point.

Colour is not the key risk indicator. Duration, recurrence, and substrate involvement are.

Red flags that should elevate concern include:

• staining that repeatedly bleeds through paint finishes
• wallpaper lifting, bubbling or detaching
• plaster that feels friable or softened
• musty or persistent odours, particularly when heating is off
• mould reappearing after cleaning or redecoration
• growth emerging from junctions, skirtings or interfaces rather than flat surfaces

These signs indicate that moisture is affecting the fabric, not just surface condensation. From a reporting perspective, they justify firmer language and clearer advice than a generic “clean and ventilate”.

Ventilation and thermal context are not optional extras

Another common reporting weakness is treating ventilation as an afterthought — or assuming that the presence of a fan or trickle vent is equivalent to performance.

Ventilation and thermal context matter as much as staining, because they explain why mould is there and whether it will return.

Surveyors should be considering:

• whether extract ventilation is present, functional, and likely to be used
• whether background ventilation is adequate for occupancy
• whether rooms appear intermittently heated or under-heated
• whether insulation continuity and cold-surface risk are obvious
• whether furniture layout is creating local microclimates

A sentence such as “improve ventilation” without explaining the underlying moisture balance tells the client very little and offers the surveyor little protection.

The orange mould example — and why knowledge gaps matter

Here is a simple but revealing training prompt:True or false: orange mould exists in dwellings.

Some surveyors would instinctively answer false. That instinct exposes a broader issue.

Orange, rust-coloured or brownish growths and staining do occur in buildings, often associated with prolonged dampness affecting timber products, paper facings, adhesives or composite materials. They are not decorative anomalies and they are not imaginary.

The issue is not whether a surveyor can name the organism. It is whether an unusual appearance is recognised as a potential indicator of longer-term moisture exposure and material degradation.

Knowledge gaps matter because they shape confidence. When something does not fit the “black mould” mental model, it is more likely to be downplayed, dismissed, or vaguely described — precisely where a more straightforward explanation is needed.

The advice gap: where many reports fall down

A recurring problem in survey reports is the gap between identification and advice.

Many reports do one of the following:

• Mention mould but give no next steps, or
• Recommend cleaning only, or
• default to “further investigation” without explaining what that means or why it matters

From a client’s perspective, this is unhelpful. From a professional-risk perspective, it is weak.

Clients are entitled to understand:

• Why the issue matters,
• What could happen if it is ignored, and
• What a proportionate next step looks like.

“Further investigation may be required” is not wrong — but it is incomplete unless framed properly.

How far should a surveyor go?

Surveyors are not expected to remediate mould, specify ventilation systems, or diagnose fungal species. But we are expected to join the dots competently.

A defensible position looks like this:

• We explain the likely moisture mechanism (e.g. condensation risk, ventilation underperformance, suspected leak or penetration).
• We explain the risk of recurrence and escalation if conditions remain unchanged.
• We advise proportionate next steps, which may include environmental correction, monitoring, targeted investigation, or specialist input where justified.
• We make clear what is outside our remit, while still explaining why signposting is appropriate.

What is no longer defensible is identifying mould and leaving the client to guess whether it matters.

Improving narrative advice — without overreaching

Good mould advice is narrative, not alarmist.

Compare:

“Mould noted on the bedroom wall. Clean and improve ventilation.”

With:

“Mould growth on the external wall and window reveal of Bedroom 2 is consistent with sustained surface condensation at cold surfaces, likely exacerbated by restricted airflow and limited ventilation. While currently localised, recurrence is foreseeable unless underlying moisture and thermal conditions are addressed. Continued exposure may result in spread, fabric deterioration and ongoing indoor air quality concerns. Further assessment of ventilation performance and thermal risk is recommended, alongside removal of contaminated finishes and monitoring for recurrence.”

The second example does not overstep competence. It explains why, what may happen, and what should be done next. It is far easier to defend.

“Further investigation” — but say what you mean

If further investigation is warranted, say what kind and why.

For example:

• Investigation to confirm the moisture source and pathway
• Inspection to establish whether substrate involvement is present
• Assessment of ventilation performance rather than just presence
• Opening up where concealed dampness is suspected

This framing shows that your recommendation is reasoned rather than generic.

The surveyor’s position, clearly stated.

Damp and mould are firmly within the surveyor’s professional territory. They are foreseeable, common, and rooted in building performance.

The expectation is not perfection. It is competence, clarity and proportionality.

That means moving beyond “there is mould” and towards:

• This is why it matters
• This is what it suggests about the building
• This is what may happen if ignored
• This is what should be done next

Do that consistently, and your reports become not just safer, but genuinely more useful to clients.

Professional context

The author is a UK residential building surveyor and researcher focusing on practitioner-led approaches to damp and mould assessment, with particular emphasis on visual diagnosis, moisture behaviour and proportionate advice in domestic surveys. Current work includes the development of structured tools and guidance aimed at improving inspection consistency, reporting clarity and professional defensibility in mould-related cases.

Click here for other articles from the author.

Authored by
Mr Kieran R. McColl, BSc (Hons) Building Surveying & Planning
PhD Candidate, London South Bank University
MCABE, MRPSA, FNIBME, FISSE

References

Building Safety Act 2022 (c. 30). London: The Stationery Office.

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Thacher, J.D., Gruzieva, O., Pershagen, G., Neuman, Å., Wickman, M., Kull, I. and Melén, E. (2017) ‘Pre- and postnatal exposure to dampness and mould and development of asthma to age 16 years’, Environmental Health Perspectives, 125(1), pp. 127–133.

World Health Organisation (WHO) (2009) WHO guidelines for indoor air quality: dampness and mould. Copenhagen: WHO Regional Office for Europe.