Background
A one-bedroom flat in a converted terraced house (circa 1900) has experienced persistent damp issues, particularly in the bedroom 🏠. Despite a chemical damp-proof course, repointing, and bathroom repairs, damp patches reappear after rain 🌧️, and wardrobes in chimney alcoves remain cold and musty 🧥🦠. Clothes in the north wardrobe develop mould, while the south wardrobe is less severe but still unusable at lower levels. The client suspects external defects, such as render or pointing, may be causing penetrating damp, and is concerned about rising repair costs. A single root cause for these issues remains unclear.
Data loggers – see damp.ai/detect
Represents Surface Relative Humidity. During the monitoring period, it remains consistently high at or near 100% RH during condensation events 💧.
Explanation: 100% RH indicates the relative humidity level at which water vapour condenses into liquid on cold surfaces. This is a critical indicator of conditions conducive to mould growth or water damage.
💙 Blue Line (Dew Point):
Represents the Dew Point—the temperature at which air becomes saturated with moisture lading to condensation 🌈.
Behaviour: The dew point is often above the outside temperature.
Recommendation: To prevent condensation, the dew point should stay below the outdoor temperature through targeted ventilation and dehumidification—a principle known as Dew’s Law 🌬️.
Context: Efficient ventilation ensures indoor vapour levels align with outdoor conditions, reducing condensation risks even during rainy periods.
🩶 Grey Line (Dew Point Differential):
Represents the Dew Point Differential, located at the base of the graph.
Behaviour: When this line is above 0°C, it indicates higher vapour levels in one space compared to another (e.g., living room vs. utility room).
Insight: In this case, higher readings suggest activities such as respiration or cooking vapours contributing to increased humidity in certain rooms.
Conclusion from data loggers
Recommendations:
Regular Monitoring: Use hygrometers to monitor indoor RH and ensure conditions remain below condensation thresholds 📉.
Targeted Ventilation: Install or adjust extractor fans to remove excess moisture, particularly in high-use areas like kitchens and bathrooms 🌀.
Dehumidification: Use a dehumidifier to lower indoor vapour levels efficiently ⚡. This not only reduces condensation risks but also warms the air through enthalpy, improving comfort 🌡️.
Curtain Management: Ensure curtains don’t block airflow near radiators or walls 🧵.
Evidence & Illustrations
This report has been carefully prepared to help you understand the true cause of the damp issue, enabling you to dry out the wall effectively. Addressing this now ensures that, when the time comes to sell the property, potential buyers won’t be deterred by signs of dampness, and their surveyors won’t feel inclined to misdiagnose rising damp or suggest the need for a so-called rising damp guarantee from a damp-proofing contractor.
Electrical sockets are prone to dampness because a section of the wall is cut out to install a metal box, which is then covered in absorbent plaster. Wiring often travels into the cold sub-floor void. These factors exacerbate the effects of both condensation and absorption of moisture.
The socket remains cold partly because it was ‘insulated’ from the radiator by the curtain . Vapourspreads through diffusion, similar to smoke (Brownian motion) 🌫️, while heat in residential settings is mainly transferred by air currents 🌬️. This is why mould and condensation often appear in cupboards, behind sofas, curtains, and similar areas 🛋️🦠.
The root cause is the vapour 💧, with the compounding factors being the cold wall and the long curtain. In almost every property, no matter how well insulated 🏡, certain areas will be close to the outside temperature. These include places near wiring or pipe entries, cold corners where air can’t flow, or behind soft furnishings 🚪🌡️.
The solution is to follow Dew’s Law 🌈: maintain indoor vapour levels—expressed as the dew point in °C—below the outside temperature through targeted ventilation and dehumidification. You can look up historic, current and forecast temperature on the metoffice.co.uk web and bbc.co.uk/weather websites.
For instance, if the indoor humidity is 40% RH at 10.5°C, then the dew point would be -2.5°C. When the outside temperature reaches -2.5°C ❄️, there is hardly any vapour, making extractor fans 🌀 far more effective than when it is warm and raining 🌧️. Our temperate, humid climate makes extractors less effective compared to dry conditions. Excess indoor vapour is more prevalent during rainy weather.
Comparison of 3 Damp Surveys 🏠💧 none contractors
Hunt & Nash RICS (2016)
- Found “relatively high damp meter readings” 📉 in the rear bedroom.
- Recommended obtaining a specialist damp contractor report 🛠️.
- Did not specify rising or penetrating damp; no cost estimate provided.
Academy Remedial Surveyors (2016)
- Diagnosed rising damp, recommending a chemical damp-proof course 💉🧱.
- Attributed the issue to neighbour’s property bridging the DPC.
- Suggested re-plastering flank wall, rear elevation, and chimney breast.
- Estimated cost: £2,000–£2,500 💷.
Damp Detectives (2022)
- Ruled out rising damp ❌.
- Identified causes as:
- Condensation/poor ventilation 🌬️.
- Water penetration from cracked bathroom tiles behind wardrobes 🚿.
- Recommended:
- Replacing bathroom tiles/waterproofing.
- Upgrading ventilation in bathroom and kitchen.
- No chemical DPC suggested.
Key Contrasts 🔍
- Academy Remedial was the only surveyor to diagnose rising damp and recommend chemical DPC 💉🧱.
- Damp Detectives focused on condensation and penetrating damp as root causes, avoiding chemical treatments.
- The RICS survey was cautious, suggesting further investigation without firm conclusions.
Takeaway 💡
Damp diagnosis varies widely. Academy emphasised rising damp, while Damp Detectives highlighted ventilation and water ingress as the primary concerns, providing the most detailed analysis. This highlights the contentious nature of chemical DPC recommendations and the importance of targeted solutions.
Unique Aspects of Our Report 🌟
- Fixing the Bathroom Extractor Fan 🛠️
- We prioritise addressing poor ventilation at the source, starting with ensuring the extractor fan operates effectively, a key factor often overlooked in other reports.
- Clear Guidance on Ventilation and Dehumidification 📏
- We explain Dew’s Law: maintaining indoor vapour levels (dew point) below the outside temperature to prevent condensation.
- Practical steps ensure you know how much is “too little” ventilation or dehumidification, helping you manage the environment effectively 🌡️.
- Progress is measurable using a damp meter, so you can confirm improvements in the wall over time 📊.
- Detailed Video Analysis 🎥
- Our video explains not just what’s happening but why. For instance, we address why rising damp is a remote possibility and how to differentiate it from other causes.
- Comprehensive Recommendations 📋
- Our report includes actionable, detailed advice, breaking down solutions step by step for clarity and ease of implementation.
To keep the property dry | |
|---|---|
| Mould Removal | |
| When mould is dry, consider sanding it down and removing it with bleach or anti-mould foam. While I personally recommend HG Mould Remover Foam Spray, the effectiveness between brands is likely similar. | |
| 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. 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. | |
| Cooking Tips | |
| Always cook with tops on pots and pans to reduce vapour emission by 80% and or use an externally ducted kitchen extractor fan – see below. Ideally keep the kitchen door closed and window open – or bathroom vent running, when it is humid. | |
| Target vapour from bathroom | |
| TIP: Keep the bathroom door closed with the fan running or window open until the humidity from the shower has subsided – typically at least 30 mins after the last shower. | |
| Target vapour from clothes drying | |
| Use a tumble dryer (like a heat pump), dry in a vented room with the door closed (possibly a bathroom with the extractor running or window open), or use a powerful dehumidifier. Don’t dry clothes in an unventilated room. | |
| Monitor dampness in wall | |
| Monitor improvements on the damp wall with a pencil line and or damp meter such as dr.wood moisture meter, logging improvements each month. | £23 |
| Use fan to expedite drying | |
| Direct a fan onto the damp patch to speed up the drying process. | £50 |
| 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 a 6.5-litre tank (£179.99, refrigerant) Duux Bora Smart Dehumidifier (DXDH02UK, £300, refrigerant) 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 capacity, tank size, low noise, continuous drainage (pipe out), and ease of programmable functions over other considerations such as weight and aesthetics. The technology is well-established and functions similarly to fridges, with a comparable fire risk profile. If these brands are unavailable, you can confidently select another alternative. When evaluating, prioritise a minimum daily capacity of 20L and continuous drainage capability (use this to drip into a sink when away in winter). Tip: Use a dehumidifier whenever leaving a property vacant. Set it to 70%RH and drip into a sink—especially in winter. This method is more efficient than other humidity management methods, including ventilation. | £180 |
| Keep objects away from walls | |
| Consider moving objects away from colds wall, including curtains and especially in corners. | |
| Check rainwater goods | |
| Check for leaks from rainwater goods, from gutters to drains and clear as required. | |
| Remedial actions – estimate of costs | £253 |
Actions if all else fails | |
|---|---|
| Consider targeted insulation | |
| Consider targeted insulation in specific areas of the home, including wall, floors, pipework, and reveals around doors and windows. A typical flat could benefit from at least £500 – £1,000 worth of targeted insulation, significantly reducing energy costs and improving thermal comfort. Focus should be given to vulnerable areas, such as cold corners, cupboards, and flank walls, where condensation and mould are most likely to occur. For spaces like cupboards, where airflow is limited, consider materials such as thermal lining paper (e.g., Wallrock) or wood fibre insulation, often marketed as floor underlay but equally effective for lining walls behind cupboards. These materials improve surface temperatures, reduce the risk of condensation, and are easy to apply in tight or enclosed spaces. While thermal lining paper and wood fibre are vapour-permeable, making them suitable for reducing condensation risks, vapour management remains essential. Insulation should always work alongside ventilation solutions, such as discreet air vents in cupboards or cold flanks, to prevent moisture build-up. I would buy a roll of Wallrock thermal lining paper to line the cupboards, focused on the cold surfaces including the base of drawers. Remember, insulation is not a standalone solution but can help reduce cold surfaces where mould tends to develop, complementing a holistic approach to moisture management. | £50 |
| Consider installing a kitchen extractor | |
| Ideally, kitchens should feature a quiet, user-friendly extractor fan strategically placed right above or adjacent to boiling pots and pans, ensuring vapour is efficiently expelled outdoors. Unfortunately, some installers overlook the necessity of outdoor ducting, effectively nullifying the fan’s purpose, or they opt for lengthy, flexible ducting that’s susceptible to damage and hampers airflow with its ridges and bends. To maximize the likelihood of its use, the fan’s noise level and ease of operation are crucial factors. A fan that operates quietly and automatically is more likely to be used consistently, enhancing kitchen ventilation and comfort. | £600 |
| Optimal actions – estimate of costs | £650 |
I conclude that the primary cause of mould and dampness at the base of the wall is excess vapour from the kitchen, bathroom and drying clothes.
Mould only grows where relative humidity exceeds 85%RH for long periods of time. The primary cause of mould is poor ventilation, insufficient air movement, made worse by cold surfaces.
I improved the flow rate of the bathroom extractor fan.. By taking a root cause approach, rather than a focus on blocking the symptoms of damp the savings are likely to be around £5,000. This contrasts with typical damp proofing contractor recommendations such as chemical treatment for rising damp and untargeted ventilation, such as PIV systems.
Flood risk: No risk See Flood Risk (note most flood risk is not from groundwater).
Sub-soil rocks: Rocks with essentially no groundwater See British Geological Survey.
Therefore risk of Rising Damp: remote possibility, see explanation by Dr Robyn Pender of Historic England.
I confirm that I inspected the property on . I conclude that the primary cause of mould and dampness at the base of the wall is excess vapour from the kitchen, bathroom and drying clothes.. 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
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.
- Rising damp concern: You were concern you might have rising damp.
- Damp treatment: Despite the low risk of rising damp, there has been an attempt at chemical treatment against rising damp. Rising damp treatment is normally a sign of insufficient ventilation. The walls have been drilled into by about 200mm and injected with damp proofing chemicals. In theory the chemicals are absorbed into the brick pores reducing the bricks ability to absorb moisture. Walls are replaced with damp proofers slurry. This can cause problems with absorption imbalance, resulting in increased condensation on other walls or vapour becoming absorbed and trapped behind the slurry. There was evidence of surface condensation in areas probably not treated with replacement plaster but no evidence of trapped vapour. The solution is through ventilation and humidity control.
“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.
Relevant examples of similar damp issues or remediation:
Vendor Lost Sale Following Damp Proofer Survey
[mwai_chatbot_v2 id=”default”] 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?
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?