Why mould often grows behind sofas


In a ground floor Victorian terrace flat, complete with a cellar and side extension, persistent damp issues have been observed in two distinct areas. The first, located in the front room, features mould originating from a corner adjoining the cellar and the building’s front wall beneath a bay window, despite previous mould treatment efforts and remedial actions addressing a misaligned drain and damp-proof injection under the bay window. Despite these measures and the provision of a dehumidifier to tenants, the problem persists, suggesting that the source of moisture may not be fully addressed. Recommendations include the installation of a ventilation system in the cellar to mitigate moisture, though skepticism remains regarding the identification of all moisture sources. The second area, at the base of the wall in the side extension, exhibits dampness and peeling paint despite treatment, indicating ongoing moisture intrusion from adjacent structures. This situation underscores the complexity of diagnosing and remedying damp issues in older properties, where multiple, interrelated factors often contribute to moisture penetration and accumulation.

image of the front of the Joint Position Statement RICS Historic England PCA (property care association) dated September 2022, featuring picture of drain


RICS (Royal Institute of Chartered Surveyors), Historic England (a public trust protecting sites of historic interest) and the Property Care Association (an association of mainly damp proofers) set out a Joint Position Statement (JPS), in September 2022 – see below.

There has long been disagreement about the causes of damp amongst surveyors. Historic England surveyors represent one extreme. They typically do not believe rising damp is a likely cause of internal dampness and rarely recommend altering walls to alleviate damp. By contrast PCA surveyors typically recommend rising damp treatment whenever they see dampness at the base of a wall and often recommend altering a building. RICS surveyors tend to be somewhere near the centre of these extremes. However, unlike Historic England and PCA surveyors, they rarely specialise in damp and often refer issues to PCA surveyors. We and most other independent surveyors are more closely aligned with Historic England’s position except that we are perhaps more pragmatic. For example, if a hole in the wall is the optimum way of solving internal dampness, then we will recommend it, but not otherwise.

JPS questions and answers

In addition to the content typically included in a professional and impartial survey report (e.g. client, surveyor and property details; limitations and exclusions), the report should include the following information:
1 A summary of the surveyor’s observations, including an Assessment of Significance.

damp and mould mainly at base of the coldest walls 4specially behind the sofa

2 The importance of regular building maintenance and how a lack of even basic maintenance can lead to problems arising. This is especially important and relevant to roofs, gutters, hidden gutters, rainwater disposal and changes in external ground levels.

As is common with all buildings, gutters and other rainwater goods should be checked twice annually, ideally during or soon after a rainstorm, for evidence of overflow and rain not being dispersed properly from the property. You should also check that there is no flow of water flow during periods of absence for signs of a leak, for instance, by note the number on the mains water meter outside your house. improve ventilation

3 An impartial diagnosis of the damp problem, which should be clearly explained and laid out systematically to communicate the relevant risks to the reader.


4 Where recommendations for the repair and recovery of moisture-affected structures are stated, the solutions should be clearly explained and prioritised as appropriate.

The solutions are explained in the Recommendations section. The primary recommendation is improve ventilation

5 The client should be provided with alternative options for which each recommendation should include advantages and disadvantages and the relevant cost and time implications.

This question is primarily directed at PCA damp proofers, to encourage them to consider methods that address the source of water not just the symptoms, such as by hacking off plaster and replacing it with slurry. You can sometimes take this damp proofing approach with short-term success. However, water will eventually find its way through. Furthermore, treatment is disruptive resulting in high cost and a poor finish, with no worthwhile guarantee of success. It likely to lower the value of the property. In our opinion you are better off trying to stop the water at its source, as we recommend. ”

6 Where monitoring and staged interventions are appropriate or beneficial, the client should be informed of the reasons for these options, together with the likely cost and time implications of such recovery strategies.

Properties should be monitored for humidity and temperature using data loggers, see datalogger section of this report. The cost of data loggers is currently less than £20 for two, aim to keep the dew point, as shown on the app screen of each logger (bottom centre on the SensorBlue), within 3°C of the external temperature, especially at night (use ventilation and/or dehumidification to reduce the internal dew point – measure external conditions or refer to weather forecasts for night-time temperatures, such as BBC Weather – a short explanation is; that this will make sure the relative humidity of all surfaces will be below the mould point even if poorly insulated). We also suggest noting values monthly using a multi-functional radio wave and conductance damp meter costing about £24 to monitor and map damp patches on internal walls. This way you can monitoring the dry progress, which typically takes 1 month per 25mm thickness of walls and more if coated. This helps determine if the root cause has been fixed or there is an additional or new source of water, and therefore more actions are required. Ideally this should be started before or soon after starting our recommendations and for about a year, repeating monthly to check progress.

7 Where appropriate, clearly state whether the building concerned represents a financial risk to the buyer or lender and why.

8 Any conflicts of interest should be clearly stated.

There is no conflict of interest. We never profit from our recommendations.

As a background, although we charge a fee for undertaking damp surveys, profit is not our primary motivator. We are motivated to:

  • solve damp problems in properties,
  • encourage clients to spend money wisely for the protection of the property and, where possible to lower the environmental impact,
  • stop or at least play our part to reduce the over-diagnosis of rising damp and so called “damp proofing” treatment by replacing plaster with chemicals and slurry, rather than dealing with the root cause.
Mould behind sofa
Ask A.I. about your report, in the “Type your message” you could ask:

What does the damp report say are the main causes of damp and main actions to stop damp?

¿Qué dice el informe de humedad sobre las principales causas de la humedad y las principales acciones para detenerla?
नमी की रिपोर्ट के अनुसार नमी के मुख्य कारण और नमी को रोकने के लिए मुख्य कार्य क्या हैं?
Que dit le rapport sur l’humidité concernant les principales causes de l’humidité et les principales actions pour l’arrêter?
Was sagt der Feuchtigkeitsbericht über die Hauptursachen von Feuchtigkeit und die Hauptmaßnahmen zur Bekämpfung von Feuchtigkeit?
Что говорится в отчете о влажности о основных причинах влажности и основных действиях по ее устранению?
Cosa dice il rapporto sull’umidità riguardo le principali cause dell’umidità e le principali azioni per fermarla?

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