Responsive Report to Identify Causes & Fix Damp
All our reports are now online, mobile friend, interactively linked to detailed glossary of terms and examples of similar issues and recommendations with A. I. integration in case you or your builder needs assistance.
In conclusion from the data loggers
- During the period under investigation the surface relative humidity on the damp floor (green line) is high, peaking at 100%RH and risking condensation on the coldest surfaces. Relative humidity is above the mould risk of 85%RH and at risk of condensation.
- The surface relative humidity is calculated considering the temperature difference between the data logger and cold surface at the time of the survey – this is an approximation and illustrative. You can check the difference more accurately with a laser thermometer on a cold night to update the interface tab in the spreadsheet.
- For each -1°C the relative humidity will be about 5%RH higher. The effect increases as the temperature difference between inside and outside increases such as when it’s cold.
- The grey line in the graph is called the dew point differential. It tells me that excess vapour is evaporating off the damp wall rather than within the kitchen as a whole, except brief periods. The most significant increases line up with warmer temperature and vice versa which tells me that evaporation from the wall is causing the increased vapour. Increased vapour is not affected b y external rain. This suggests to me that the cold water pipes are acting a bit like a dehumidifier, taking water out, passing it into the wall, which it then evaporates out of.
- It is interesting that there is no increase in the external (light blue) dew point relative to the kitchen despite some heavy rain around 26 – 27 September, this suggests that penetrating damp is not a root cause, at least not significantly.
- The example property dew point is in fact from my house, where I run a dehumidifier to maintain a healthy environment and reduce the need for and cost of heating. The difference between your dew points and the example property are narrowing suggesting ventilation improvement and or drying.
- Overall, there clear signs of condensation being the root cause. Data loggers will be useful for ongoing monitoring following the implementation of my recommended actions. Working from home results in more cooking and more respiration. The energy crisis has resulted in people turning down the heat in unoccupied rooms and closing vents and windows. Risk of condensation can be reduced with a 20L+ dehumidifier.
|Damp stain on internal rear wall either side of patio doors which is getting worse.
In my opinion, the primary cause of damp in the corner comes from condensation forming on the pipes under the boiler, but external damage to tiles could be adding to the damp through ingress, that is penetrating damp.
Evidence & Illustrations
To keep the property dry
|Seal cracks and gaps on external tiles and coatings
|Instruct a general builder to fill gaps and cracks between tiles and between the wall and external tiles and with a water-proof grout. Any cracks in the render should also be filled with an external acrylic caulk for small gaps less than 3mmor a similar material to the original render, probably a cement-based mortar, for larger gaps (>3mm).
|Check water flowing into sub-floor air brick
|This is a tricky recommendations as you don’t want to lose ventilation. However, the lowest run of holes in the air vents looks vulnerable to rainwater pouring in. You could seal these up, but the best approach is to see what happens during a rainstorm, when wind is directed to the holes and monitor sub-floor relativity.
|Monitor sub-floor humidity
|Use a hygrometer probe under or near damp wall (left in place during survey). A probe can be pushed through cracks in floorboards or by discretely drilling out a hole. The sub-floor relative humidity will fluctuate. If it remains above 85%RH for an extended period then consider installing a fan into the sub-floor to blow air out. Increasing ventilation is tricky as there is limited accessibility. A company called ELTA made a Sub-Floor Ventilation Fan, which many clients with similar issues have installed with success, but ELTA have been closed down. This site seems to offer the same unit: https://www.builders-superstore.co.uk/product/ventilation-fan-sub-floor-mains-powered/
|Insulate around all water pipes, especially cold water, also consider insulating the wall under the cupboard and behind the kitchen units.
|Target vapour from bathroom
|Ask tenants to 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. Consider adding a spring to the bathroom door as an extra reminder.
|Target vapour from cooking
|Ask tenants to cook with tops on pots and pans to reduce the production of vapour from cooking by 80%. Run the kitchen extractor fan when cooking and, or if humid.
|Target vapour from clothes drying
|Ask tenants to 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.
|Monitor vapour with data loggers
|Monitor relative humidity and temperature against the wall or ceiling to observe the effects of improvements, such as ORIA Wireless Thermometer Hygrometer (20m (2 Packs)) – already in place. When away from a property, such as landlords, consider monitoring remotely with a WIFI linked logger. In addition monitor improvements on the damp wall a pencil line and damp meter, logging improvements each month.
|Stay above the mould and dew points
|Dew point is the temperature that condensation starts at. Either reduce vapour and or maintain heat especially late at night when it’s cold outside: More efficient alternatives include 1) insulating cold walls, 2) strategically placing one or more dehumidifiers, positioned where the night-time dew point is highest – use data loggers to locate the optimal position (typically a damp room near a damp wall, e.g., kitchen, bathroom). Personally, I run a dehumidifier whenever leaving a room unheated.
|Maintain airflow close to cold walls
|TIP: Keep objects away from walls where condensation or mould has built up. Consider insulating cold internal surfaces, for example, with floor insulation from B&Q or Wallrock Thermal Liner (ensure to use Wallrock Thermal Liner Adhesive).
|Remedial actions – estimate of costs
Actions if all esle fails
|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 daily and tank capacity, low noise, whether it has a pipe out and easy 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).
|Consider replacing the bathroom extractor
|In my opinion, the optimal fans are ones that are targeted, with the fan located near the shower head (without being so close that water sprays onto it), removing vapour during and for at least 30 minutes after taking a shower or bath (which typically produces slightly less vapour). Ideally the fan should be separately wired up with an overrun. Installing the overrun can account for a majority of the cost. Consider installing a continuous flow extractor fan such as Brookvent Airstream DMEV 100 HT (Continuous Running Extractor Fan with Humidistat Timer). Note a continuous flow fan will expel warm air, thereby increasing heating cost by about £120 p.a. but this may be a small price to pay. You can use an isolator to manually turn off the fan when the property is sufficiently ventilated, but the risk is it is left off.
|The UK has pledged to reduce its greenhouse gas emissions to net zero by 2050. You can expect energy savings of approximately 5% – 10% p.a. for the first £1,000 to £2,000 spent by being selective in your approach. This recommendation serves as a starting point for discussion. You should assess whether this approach aligns with your financial and practical needs.
|Remedial actions – estimate of total costs
I conclude that there is no evidence of rising damp, which comes from groundwater in contact with walls. The risk of groundwater is very low. The damp patch is more or less colourless suggesting that the damp is not primarily caused by ingress. The sub-floor air bricks are low to the ground, the void has high humidity and therefore there is a risk of condensation forming in the sub-floor void. There were also many signs of excess humidity causing condensation and mould, and a risk of condensation forming on a cold water pipe.
Having studied extensive data from data loggers, the hygrometer probe and taken damp meter measurements, I think there are multiple sources acting together. 1) Rainwater entering the sub-floor void, possibly through splashing into the air brick, then condensing on the DPC. 2) Gaps in tiles letting water into the wall. 3) Condensation from the main part of the property forming at the cold base of internal walls. 4) Condensation causing damp on the cold water pipe under the cupboard. All could be caused by internal condensation as vapour pressure is igh, so which you should do the easy things like grout around tiles first, your focus should be on reducing and monitoring internal vapour, before more extensive works. It is possible that the hygrometer probe is being influenced by internal humidity in the property, keep monoting it befoe considering more extensive solutions.
I increased the bathroom extractor fan overruns from 5 minutes to 30 minutes.. 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 Damprising damp is a remote possibility, see explanation by Dr Robyn Pender of Historic England.
I confirm that I inspected the property on 20 September 2023. I conclude that there is no evidence of rising damp, which comes from groundwater in contact with walls. The risk of groundwater is very low. The damp patch is more or less colourless suggesting that the damp is not primarily caused by ingress. The sub-floor air bricks are low to the ground, the void has high humidity and therefore there is a risk of condensation forming in the sub-floor void. There were also many signs of excess humidity causing condensation and mould, and a risk of condensation forming on a cold water pipe. 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 dataloggers for example the Smart Hygrometer measuring humidity on the wall and nearest source of vapour, before and after following our recommendations. These dataloggers 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.
Site visit 20 September 2023
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.
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.
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.
W.H.O. indoor air quality guidelines
“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 (the ceond in aseries won’t add as much)
- 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 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 dehumidifer or window open, never on radiators or heated rail without a door closed and 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 properties with similar damp issues: electric-sockets
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?
What language does your builder speak?
The report is written in English, but is translated into the following popular languages often heard in London: Arabic, Bengali, Chinese, French, German, Gujarati, Italian, Polish, Portuguese, Punjabi, Romanian, Spanish, Tamil, Turkish, Urdu ... and many more, just ask.