Background
A Victorian terraced house with underfloor cavity, or void, is suffering from multiple damp-related issues. 🌿 Rising damp ⬆️ is suspected, with colourless damp patches observed both above and below ground level. Dots at the base of the wall show that the property has previously been damp-proofed against rising damp 💉🧱.
In the kitchen, damp patches in several locations suggest possible water ingress 🌧️, though the exact source remains unclear. Upstairs, a previous issue linked to a leaking neighbour’s roof 💧onto a party wall has reportedly been resolved.
The property owners are seeking expert advice to address damp in a sustainable and cost-effective manner, estimating the costs for remedying the issues. Their goal is to ensure long-term solutions rather than temporary fixes. ✨
Data loggers – see damp.ai/detect
💚 Green Line (Surface Relative Humidity):
Represents the surface relative humidity. During the monitoring period, there are significant high surface relative humidity events or spikes, which appear to correlate with cooking activities rather than sudden cooling of the surface. High relative humidity at these times suggests vapourgeneration from cooking as the primary source.
💙 Blue Line (Dew Point):
Represents the amount of vapour in the air. To prevent condensation, the dew point should stay below the 🩷 Pink Line (Outdoor Temperature), in accordance with Dew’s Law. A high dew point indicates excessive moisture in the air, which requires ventilation and dehumidification to manage.
🩶 Grey Line (Dew Point Differential):
Represents the difference in vapour levels between the study and the kitchen, shown at the base of the graph. The grey line indicates that more vapour is generally generated in the study compared to the kitchen, except during cooking events, when the kitchen contributes higher vapour levels. This suggests localised activities are influencing vapour levels significantly.
Conclusion from data loggers
- High humidity spikes align with cooking, suggesting inadequate vapour control in the kitchen during these times.
- The dew point is consistently too high, increasing the risk of condensation.
- Vapour generation is generally higher in the study, except during cooking events.
Recommendations:
- Improve ventilation in the kitchen, particularly during cooking, by using a functioning extractor fan vented externally.
- Monitor vapour sources in the study and explore ventilation options to manage consistent vapour generation in that space.
- Consider dehumidification measures to maintain lower dew point levels across the property.
Evidence & Illustrations
As the saying goes; ‘when the fix fails, it’s likely the fault wasn’t found.’ That is the cause isn’t rising damp, and damp-proofing isn’t the right treatment.
Some say differentiating between rainwater in soil and groundwater is being pedantic. I disagree as rainwater will be naturally drawn down through capillary action and gravity to the zone of saturation. The zone of saturation is the groundwater. The rise of rainwater above unsaturated soil is minimal, about 10cm, and he rise of rainwater above unsaturated soil is minimal, about 10 cm, and is typically confined to sub-floor level brick.
Other matters
To keep the property dry | |
|---|---|
| Cracked Rainwater Gulley | |
| A blocked or cracked underground rainwater pipe or gulley can cause serious problems, such as dampness, rot, or even subsidence. lack of water in the gulley, is likely to indicate an underground crack allowing water to escape into the sub-floor void. Addressing these issues quickly is vital. Options include hiring a CCTV drain company or installing an alternative drainage solution, such as an elbow and a 2-metre pipe discharging water away from the house. I would discharge the Aco drain onto the street, by drilling a hole below the front wall and blocking the drain to your neighbour’s side, at least until any underground cracks are repaired. Read more online at damp.ai. | £100 |
| Check rainwater goods | |
| The front gutter with a gutter clearer or instruct a roofer or gutter clearer to clear it. I would advise using a ladder. Check rainwater goods every 6 months, during a rainstorm or soon after for signs of overflowing water – fixing rainwater goods as appropriate. | £500 |
| sub-floor rot | |
| A piece of timber supporting a joist is rotten. It does not appear to be significant or original. If it were to fail, it would likely drop gradually, posing no immediate safety concerns. Rot will cease to progress once the water source is removed or vapour levels in the sub-floor void are reduced, though some damage may remain. The primary challenge is access rather than the cost of timber. Acting quickly to reduce moisture and monitoring sub-floor relative humidity and the timber condition should help you avoid the need for repairs. | |
| Monitor sub-floor relative humidity | |
| Place one data logger in the sub-floor void and another outside. Compare the relative humidity and dew points recorded below the floor with those outside. Aim to increase sub-floor ventilation (see evidence section above) until the sub-floor humidity consistently tends towards 85% RH or below, and the internal dew point is regularly within 1°C or less, of the external dew point. Dew points indicate the amount of vapour in the air and are a critical measure in assessing moisture levels. Both readings will be influenced by air from the property. Efforts should be made to minimise vapour travelling from the house into the sub-floor void, where it could condense and exacerbate moisture-related issues. | £20 |
| Monitor dampness in walls | |
| Mark improvements on damp walls with a pencil line or sticky note and use a moisture meter, such as the Dr. Meter Wood Moisture Meter 2 in 1 Pin & Pinless Multifunctional Water Detector £23.99 or similar damp meter, to log and monitor reduction to dampness in walls. By doing so, you will gain early confidence in these recommendations. | £23 |
| Reduce vapour from cooking | |
| Cook with tops on pots and pans to reduce the production of vapour from cooking by 80%. | |
| Use a dehumidifier | |
| Maintain relative humidity, especially at night when it’s cold outside, with a dehumidifier such as the PureMate 20L/Day Portable & Compact Dehumidifier with a 6.5-litre tank (£179.99, refrigerant), the Duux Bora Smart Dehumidifier (DXDH02UK, £300, refrigerant), or the 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 well-established and easy to manufacture with a similar function and fire risk profile to fridges. 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). I use a dehumidifier whenever leaving a property vacant, dripping into a sink, set to 70%RH, especially in winter – it is more efficient than other humidity managing methods including ventilation. | £180 |
| 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. | |
| 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. | |
| Remedial actions – estimate of costs | £823 |
Actions if all else fails | |
|---|---|
| Target vapour from cooking with an extractor fan | |
| Consider installing a kitchen extractor fan, ducted out. | £800 |
| Hygroscopic salts | |
| The front chimney is at risk of hygroscopic salts. I would treat the gulley and internal vapour first. So this is advice should those things fail to reduce damp in the wall after about 6 months or so. Hygroscopic salts may resemble grease stains but rest assured, they’re harmless. They don’t cause damage or mould, yet can appear unsightly, especially during summer heatwaves, potentially complicating property sales or rentals. Keep this report handy to reassure prospective buyers of their benign nature. Effective Solutions: The prime method to conceal these salts involves an impermeable blocker with at least 300mm overlap, preventing the spread of any damp appearance. Aim for a uniform treatment across wall sections to ensure consistent humidity interaction. Remember, these salts often lurk just below the surface. Cost-Effective Remediation Methods: Zinsser Cover Stain: The simplest, most affordable approach. Two coats of this solvent-based primer-sealer should do the trick, costing about £15 plus potential labour. It’s user-friendly, easy to remove and reapply, making it ideal for DIY fixes. For larger areas, consider a gloss paint layer between two Zinsser coats for uniformity. This is a homeowner-friendly task but can also be efficiently tackled by a builder as part of a bigger project. Sempatap/Wallrock: Ideal for mildly cold walls, this lining paper creates a barrier, offering slight insulation. It’s a half-day job costing about £100 per linear metre. Thermal Insulating Plasterboard: For very cold walls, removing plaster and installing this board with a vapour barrier is best, mirroring professional damp proofing. It’s a day-long task, costing around £400 per linear metre. Note on Damp Proofing Slurry: Often less effective, as it can activate salts, it’s also invasive and costly. Starting Point: Zinsser Cover Stain is your go-to. It’s budget-friendly and effective for immediate action, with the option to escalate to plasterboard installation if necessary. Humidity Management: Excessive humidity can highlight salts at the impermeable material’s edge. If this happens, a second Zinsser application is recommended. | £50 |
| Optimal actions – estimate of costs | £850 |
I conclude that the primary cause of dampness in the ground floor chimney breast is water in the sub-floor void, causing condensation on the damp proof course, resulting in rising damp-like symptoms.
I believe the high sub-floor relative humidity is coming from your neighbour’s gulley, which should be full of water, but it is not. This suggests there is a crack in the gulley. There are other issues, including excess vapour and a blocked gutter.
By taking a root cause approach, rather than a focus on blocking the symptoms of damp the savings are likely to be around £10,000. This contrasts with typical damp proofing contractor recommendations such as chemical treatment for rising damp and untargeted ventilation, such as PIV systems.
Flood risk: Risk of surface water (i.e. penetrating damp from rainwater, not rising damp from groundwater) See Flood Risk (note most flood risk is not from groundwater).
Sub-soil rocks: Near low productive aquifer with intergranular flow See British Geological Survey.
Therefore risk of Rising Damp: highly unlikely, see explanation by Dr Robyn Pender of Historic England.
I confirm that I inspected the property on . I conclude that the primary cause of dampness in the ground floor chimney breast is water in the sub-floor void, causing condensation on the damp proof course, resulting in rising damp-like symptoms.. 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.
“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:
Home Buyer Surveyor Claims Rising Damp Without Evidence
[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?