Background
A detailed investigation was requested for a property with multiple damp issues, including white salts, brown stains, and colourless patches above ground. Visible damage, such as bubbling paint and discolouration around a uPVC window, was noted on a ground-floor external wall, staircase walls, and near a radiator. Despite a gutter survey and roof repair, the problems persist.
Data loggers – see damp.ai/detect
In the above the data is for the kitchen. When the grey line is dew point differential line; below 0, more vapour is recorded on the second data logger relative to the first. We can see times of day when vapour is being produced by the kitchen. When comparing to the first graph, we can see more vapour is coming from the kitchen relative to the bathroom.
Conclusion from data loggers
There has been a dramatic improvement in the surface relative humidity, reducing the risk of condensation – well done.
Evidence & Illustrations
B) There is a gap between the render and the pipe. The metal in the pipe will expand and contract at a different rate from the render, increasing the risk of cracks around and behind the pipe. This could also lead to pipe rust and leakage, which often goes unnoticed.
B) There is a line in the render. It is probably nothing to worry about. However, render applied at different times can crack along the seam. I didn’t observe a crack.
C) I didn’t observe cracks in the short flat floor section acting as a cover above the front door.
The white salts are calcium sulphate salts, that come from plaster. They are benign, normally a sign of repeated cycles of evaporation and condensation and can simply be rubbed away with sandpaper prior to redecoration.
Other matters
I couldn’t locate the vent outlet for the top floor bathroom extractor fan. While it is unlikely to have a direct effect on ground floor damp, if my suspicions are correct, there is a risk of vapour being blown into the roof void, leading to a risk of condensation in the roof and potentially dampness and rot. If you can, I recommend asking the builder for details on the vent’s outlet. If in doubt, or my suspicions are confirmed, stop using the vent, open the bathroom window, and keep the door closed instead – the old fashioned way or consider installing a new vent and outlet, ideally in a way that you can check it.
To keep the property dry | |
|---|---|
| Check rainwater goods | |
| Inspect rainwater goods (gutters, downpipes, etc.) every six months, ideally during or shortly after a rainstorm, to check for overflowing or leaks. Fix any issues as needed to ensure proper water drainage. | |
| Fill render crack | |
| Address visible cracks in the exterior walls, and search for hidden cracks, including around the downpipe. If the downpipe is leaking, repair or replace it, see below. For small cracks (up to 3mm), use an acrylic-based caulk; for larger cracks, use a cement-based mortar. Rake out cracks to remove loose material before filling. Filling all visible cracks may solve the ingress issues, but hidden cracks, particularly around the downpipe, and differing expansion rates between metal and render suggest further treatment might be necessary, see the “if all else fails” section below. | £300 |
| Reduce vapour from cooking | |
| Cook with tops on pots and pans to reduce the production of vapour from cooking by 80%. | |
| 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. | |
| 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. | |
| 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 |
| Remedial actions – estimate of costs | £503 |
Actions if all else fails | |
|---|---|
| Replace the downpipe | |
| Replace the damaged metal downpipe with a plastic alternative, potentially replacing all front guttering for uniformity. Ensure gaps and cracks are sealed, particularly where the downpipe connects to the wall. The estimate includes materials, a two-day labour cost, and platform hire for access. | £2,000 |
| Consider EWI | |
| Install EWI, external wall insulation, on the flank wall after filling cracks and removing the downpipe. This will reduce heat loss and mitigate the recurrence of penetrating damp. Extend the gutter to accommodate the insulation and reposition the downpipe away from the wall. The estimate includes prior costs (£2,000 for the downpipe and gutter replacement and £1,000 for crack repairs). | £10,000 |
| Optimal actions – estimate of costs | £12,000 |
I conclude that the primary cause of internal dampness is render cracks near and behind the downpipe on the flank wall, worsened by excess vapour from insufficient ventilation.
The brown stain shows that there has been penetrating damp. There are visible cracks in the render and a risk of hidden cracks behind the downpipe.
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: , see explanation by Dr Robyn Pender of Historic England.
I confirm that I inspected the property on . I conclude that the primary cause of internal dampness is render cracks near and behind the downpipe on the flank wall, worsened by excess vapour from insufficient ventilation.. 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:
See past damp cases
[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?