Background
The issue has been ongoing for some time, and the root cause has yet to be determined. The wall was treated with a mould eradication solution, but this does not appear to have resolved the problem. An assessment is requested to identify the root cause and provide recommendations for rectification. If the cause is internal, it will be the landlord’s responsibility to address. If external, the matter will need to be escalated to the council.
Awaab’s Law and Dew’s Law
Awaab’s law establishes a legal responsibility for landlords to address hazards in UK rental properties promptly. These hazards include damp and mould – see legal requirements for further details.
Dew’s Law is a principle that dictates internal vapour, measured as the dew point temperature, should always be kept below the external temperature. This is important because:
- The dew point is the temperature at which the air’s humidity reaches 100% relative humidity(RH), leading to condensation, and for longer periods at 85%RH; mould.
- Most properties have cold zones, particularly near the external walls, especially their corners or tops or walls, or around cold water pipes, which are often at or near the external temperature.
- Ventilation replaces internal air with external air, but without additional heating or dehumidification, irrespective of insulation and ventilation, there is a risk of condensation and mould, even in summer and even in unoccupied properties.
Every property is at risk of mould and condensation
By monitoring internal vapour, expressed as °C and comparing it to the outside temperature and forecast temperature a property can be proactively heated, ventilated and or dehumidified to ensure the risk of mould and condensation is minimised. Monitoring is best achieved remotely and with occupiers, so that they are engaged as part of the solution.
Data loggers – see damp.ai/detect
I haven’t received any data from the loggers placed in the property. There are no signs of penetrating damp. f damp were penetrating, there would be an obvious brown stain, typically a single centre of dampness or point of entry, and mould, if present, would be more concentrated close to the point of entry.
Internal versus external cause
I don’t believe the issue is external per se. However, the construction, with large amounts of external surface area, and lack of built-in ventilation, compounds the risk of mould. The council, as freeholder, should be asked to help you resolve these risks.They are the ultimate landlord and therefore presumably share some of the responsibilities under Awaab’s Law with regards to ventilation and should help with insulation, given the insulation design and construction is a compounding factor.
Mould risk in unoccupied properties
The property is vacant so no vapour should be being generated by occupants. Unoccupied and unheated properties are at risk of mould even with ventilation. The external air is at 100% relative humidity (RH) when it is raining. So even with ventilation alone, where internal air is replaced with external air, there is a risk of regularly exceeding 85%RH relative humidity, resulting in a mouldrisk. The easiest and most cost effective solution is to run a dehumidifier, draining into a sink, or similar.
Evidence & Illustrations

To keep the property dry | |
|---|---|
| Remove mould | |
| Consider sanding down mould where dry, and removing it with either bleach or anti-mould foam. I personally use HG Mould Remover Foam Spray, though other reputable brands should provide similar results. | £100 |
| Tenancy agreement for damp | |
| Update the tenancy agreement, see Tenants’ responsibility to stay mould and damp free. Tenants should monitor humidity levels, use a dehumidifier, remove mould if it reappears, and communicate with the landlord or agent. Dealing with damp and mould requires teamwork, communication, and an understanding that it is not always easy for tenants, nor do they necessarily fully comprehend their challenges and responsibilities. | |
| Improve bathroom ventilation | |
| Install bathroom extractor fan, ideally a continuous flow bathroom extractor fan such as Brookvent Airstream DMEV 100 HT (Continuous Running Extractor Fan with Humidistat Timer) – I have installed one in a rental property I own myself, that was bought cheaply because of mould. Although important to have an isolator, it can be sited in a way that doesn’t tempt tenants to use it. Ideally the vent should be located away from the door, closer to the shower. Ideally the ducting should be rigid, for reduced air resistance, and insulated to reduce risk of condensation in pipe. I would also install a bathroom spring to encourage tenants to keep the door closed. | £700 |
| Target vapour from cooking with an extractor fan | |
| Consider installing a kitchen extractor fan, ducted out. The best fans are sited above the hob, in the form of a hood, they need to be ducted out with a minimum airflow of 30 litres per second. Alternative provide a 150mm kitchen extractor fan, sited in the window, as your neighbours have – the council should have people available to install this, as they probably own the windows. These fans need to have a 60 litre per second capacity. I would consider making the fan sensor activated, with a 30 minute overrun. I would consider installing a spring on the kitchen door. | |
| Use a dehumidifier | |
| Maintain relative humidity, especially at night when it’s cold outside, with a dehumidifier such as PureMate 20L/Day Portable & Compact Dehumidifier with 6.5 Litre (£179.99 Refrigerant), Duux Bora Smart Dehumidifier (DXDH02UK £300 Refrigerant) or Meaco DD8L Zambezi (£260 Desiccant – best for colder environments) – Which! Best buys. There are plenty of alternatives available. I choose a dehumidifier based on daily and tank capacity, low noise, whether it has a pipe out, and ease of programmable functions over other considerations such as weight and aesthetics. The technology is old and easy to manufacture. So if these brands are not available, you are sure to find another alternative. Evaluate based on daily capacity (20L minimum) and whether it has a continuous pipe out (use this to drip into a sink when away in winter). | £180 |
| Target vapour from clothes drying | |
| Either provide a tumble dryer (like a heat pump), or provide a powerful dehumidifier. Don’t allow tenants to dry clothes without using a dehumidifier, especially in an unventilated room. | |
| Follow Dew’s Law | |
| Follow Dew’s Law to effectively manage internal vapour, it is crucial to maintain the internal vapour levels, as measured by the dew point in degrees Centigrade, below the external temperature. This can be achieved through adequate ventilation and the use of dehumidifiers. Monitor the internal Dew Point with a reliable device, such as the Habotest Hygrometer or Dew Point Meter HT607, or utilise the sensorblue app paired with the ORIA Wireless Thermometer Hygrometer. Govee Thermo-Hygrometer and other WIFI smart meters provide continuous monitoring of humidity levels in problem areas and send alerts when levels are too high, helping tenants to proactively manage moisture before mould forms. These tools help in accurately gauging humidity levels, ensuring they remain optimal. For more detailed information on detecting and managing damp issues, please visit https://damp.ai/detect. | |
| Remedial actions – estimate of costs | £980 |
Actions if all else fails | |
|---|---|
| Consider installing insulation | |
| Consider installing thermal insulating plasterboard or thermal lining paper, such as Wallrock thermal liner or Sempatap thermal solid wall insulation to cold surfaces, with a thick insulating underlay below the flooring – ask the council, as they may be planning to install EWI (External Wall Insulation). | £2,000 |
| Anti-Mould Coatings | |
| Consider painting vulnerable areas with anti-mould paint, this is not instead of the above. | £100 |
| Consider insulating pipes | |
| Pipe insulation will reduce the risk of dampness caused by cold pipes. | £10 |
| Education for Tenants | |
| Consider providing educational materials (e.g. leaflets, guides, or even a video – see video to this survey) to tenants on how to reduce moisture, the importance of using extractor fans, and proper ventilation techniques. This would help reduce recurring issues with mould and damp. | |
| Regular Property Inspections | |
| Consider scheduled property inspections (e.g. every month initially, then every six months). This ensures that tenants are managing moisture levels and any maintenance issues can be caught early, such as blocked vents or malfunctioning extractor fans. | |
| Optimal actions – estimate of costs | £2,110 |
I conclude that mould from excess vapour from insufficient ventilation, with an increased risk caused by poor insulation.
Mould only grows where there is excess vapour. Vapour can only be controlled with targeted ventilation and dehumidification. Heat loss is a compounding factor, but not the root cause. Ventilation, dehumidification, insulation, monitoring relative humidity, and working with tenants to ensure they understand and respond to excess vapour will reduce the risk of mould growth.
. By taking a root cause approach, rather than a focus on blocking the symptoms of damp the savings are likely to be around £2,000. This contrasts with typical damp proofing contractor recommendations such as chemical treatment for rising damp and untargeted ventilation, such as PIV systems.
Flood risk: Low risk See Flood Risk (note most flood risk is not from groundwater).
Sub-soil rocks: Near moderately productive aquifer with intergranular flow See British Geological Survey.
Therefore risk of Rising Damp: low risk, see explanation by Dr Robyn Pender of Historic England.
I confirm that I inspected the property on 240909SH1230. I conclude that mould from excess vapour from insufficient ventilation, with an increased risk caused by poor insulation.. All buildings can be exposed to unvented vapour and external dampness to some degree. You will mitigate the risk of damp if you follow all our recommendations. This report is intended to be read in full including supplementary links in this report. Observations and opinions must not be taken in isolation. Given the right weather conditions almost any house can be affected by rain. Like any building, you need to be aware of the risks of damp arising in the future and should plan a programme of monitoring, prevention and maintenance accordingly. Damp Surveys Ltd reports are designed to provide you with an informed, independent expert opinion as to the cause of dampness in the property, together with any recommendations for further investigation or remedial work. We do not warrant any findings in this report unless we enter into a separate warranty agreement with you.
The survey was conducted during daylight hours. Damp will be more noticeable at night and when the weather is colder and more humid. Gutters are more likely to fail when full of leaves and during periods of prolonged rain and adverse wind. We make best endeavours but cannot guarantee being able to identify all forms of damp, rot and insect infestation affecting the property.
We carried out a careful and thorough inspection of as much of the property as was accessible. However, when a full inspection is not possible, we make a professional judgement regarding the likelihood of a defect being present. In certain circumstances, this may lead to a recommendation for further action to open up an area for additional investigation. We were unable to inspect the entire roof, all the guttering, and some of the drains. Similarly, inspection of woodwork or other parts of the structure that were covered, unexposed, poorly lit or inaccessible such as in the loft, cellar, or sub-floor void was not possible, and therefore we are unable to assert that such parts of the property are free from defect. There were no obvious signs of damp resulting from these limitations
Negligence claims must be made within 90 days of the damp survey site visit. Clients must make best endeavours to monitor humidity and temperature on a damp wall and the closest source of humidity, by purchasing and placing two data loggers for example the Smart Hygrometer measuring humidity on the wall and nearest source of vapour, before and after following our recommendations. These data loggers have sufficient memory capacity to store 90 days of data.
This report is for the sole use of the client (named on the invoice, but omitted here for anonymity) for whom the survey was undertaken and can only be relied upon for 90 days from the survey date. Unless expressly stated otherwise in this report, nothing in this report confers or is intended to confer any rights on any third party pursuant to the Contracts (Rights of Third Parties) Act 1999.
Simon Hichens
Site visit 240909SH1230
Simon Hichens BSc Chemistry RICS Qualified Expert Witness (Chartered Surveyors)
PCA Certificated Surveyor of Dampness & Timber in Buildings (Property Care Association)
Damp Surveys Ltd, 119 Longton Ave London SE26 6RF Reg. 10977488 (England & Wales)
Founder of damp.aï & Member of the Society for the Protection of Ancient Buildings (SPAB)
Our damp surveys are designed to provide a holistic diagnosis that identifies and deals with causes rather than a focus on symptoms. Symptoms will disappear over time, once damp is stopped at source. We look for risks of dampness, but unless moisture is present, we can’t guarantee to identify all risks of future moisture. Our reports:
- identify root cause(s) of major unwanted dampness within the property,
- identify major symptoms of unwanted dampness,
- identify major structural damage caused by dampness,
- recommend actions and estimated costs to stop damp at source and mitigate its effects,
- recognise that treating damp is often a staged approach, treating obvious causes first.
Understanding damp
For survey purposes, damp is defined as unwanted water. Water brings life. We need it. Unfortunately, fungus and insects also thrive in water. While a damp wall can cause decorative spoiling, it is not moisture, but the life it brings that causes the greatest concern in the home environment. FACT: vapour causes 85% of residential damp problems.
Independence and Methodology
Our only income is through damp survey fees. We are independent of contractors and never profit from remedial work. We do not receive or pay any fees or other inducements. Our motivation is peace of mind and practical, durable solutions. We use an array of equipment to identify the root cause of damp within walls. Our damp surveys follow guidance from RICS, Historic England and PCA joint position statement and support RICS’s highest standard, level 3 “Home Survey Standard” (HSS).
During the survey we assess likelihood of rising damp*, mainswater leak, penetrating damp, condensation, timber rot and woodworm. We profile the damp patches and consider the likely sources of dampness and test ventilation against building regulations requirements. We consider changes to the property and factors just before the first sighting of damp.
“Management of moisture requires proper control of temperature and ventilation to avoid excess humidity, condensation on surfaces and excess moisture in materials. Ventilation should be distributed effectively throughout spaces, and stagnant air zones should be avoided.”
FACT: Houses contain 30 – 40 litres of water as vapour typically. Each day, each occupant adds on average about 1.5 litres as follows:
- Each shower results in 1/2L condensing (each additional shower in a series won’t add as much as the first, so long as the door is kept closed)
- Vapour from drying clothes releases about ½ litre per day if dried indoors
- Respiration releases about ¾ litre per day (of which ¼ l at night)
- Cooking produces about ¼ litre per day per person
- Unvented vapour can cause condensation, mould and allergenic dust mites. The simple rule for keeping your property dry and mould free is;
- Vent out as much vapour as produced, each and every day!
- Central heating and double-glazing reduce background ventilation. To overcome this you should use mechanical extractors. Where properties are rented, consider using monitoring devices (such as a Govee WIFI hygrometer) and if necessary, install continuous flow extractors, but beware there can be a thermal cost caused by continuous heat lost.
FACTS about Condensation and Mould
- FACT: warm air holds more water vapour than cold air. The warmer it is, the more air’s capacity to hold water vapour. Conversely the colder it is, the less capacity, until air cannot hold any more vapour. We call that the dew point or 100%RH. As soon air reaches capacity, condensation will form on the coldest surfaces.
- FACT: Mould and dust mites
- FACT: Mould only grows when air is humid for long periods. In the occupied home environment, it is 6 hours over 85% RH. For properties that are unoccupied for long periods, it is 75% RH for many days of consistent and high humidity. Avoid allowing the surface relative humidity of cold walls to exceed 85% RH by ventilating, dehumidifying, insulating, and ensuring airflow, particularly in cold corners, base of walls and ceilings, eaves, and cold window and door reveals.
- FACT: Dust mites are microscopic insects that can cause allergies. They grow in similar conditions to mould. So ventilate more to avoid allergies.
- FACT: Health concerns: There are no health and safety issues from damp noted. It is in the occupier’s interests to keep a property properly ventilated or dehumidified and temperatures above the dew and mould points throughout the property, thereby reducing the health risk associated with dust mites, bacteria, protozoans, as well as decorative spoiling caused by mould.
TIPS To Stay Condensation and Mould Free
- TIP: Reduce the production of vapour at source:
- TIP: Keep bathroom extractor fans running, or window open for at least 30 minutes.
- TIP: Keep bathroom doors closed at all times, and bathroom windows open safely.
- TIP: When filling the bath, run the cold water first then add the hot.
- TIP: Dry clothes outside, in a dryer, in a closed room with a dehumidifier or window open, never on radiators or heated rail without a door closed and a means of removing the vapour.
- TIP: Cook with tops on pots and pans, avoiding excessive boiling.
- TIP: Keep the kitchen door closed and extractor fan on where possible.
- TIP:Mechanical vents are best, but if you only have passive vents, such as a whole in the wall or chimney, then vents open with space for air to move, insulate where possible.
- TIP: Keep trickle vents open or alternatively, open windows on safety locks.
- TIP: Stop mould forming:
* Maintain external wall temperatures above 12°C, with low background heating.
* Declutter leaving space for warm air to circulate around cold surfaces.
* Where possible, avoid placing wardrobes and furniture against external walls.
* Avoid overfilling wardrobes and cupboards as it restricts air circulation.
* Use dehumidifiers or small wardrobe dehumidifying bags and replace regularly.
* Wipe mould and condensation off walls and clothes as soon as it appears. - TIP: Monitor relative humidity
* We recommend monitoring temperature and relative humidity with a data logger to see what is happening.
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?
潮湿报告说什么是潮湿的主要原因和防止潮湿的主要措施?
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?
