Data loggers
See https://damp.ai/glossary/monitor-humidity-with-data-loggers/ on how to use the data logger app. To work out the external dew point, you can install a logger outside and look at the dew points indicated on the logger app (for example SensorBlue), or as a rough guide if you pick up the Met Weather, look up your area, then take the external temperature and external relative humidity then take off 1° for each 5% below 100%RH to estimate the dew point. So for instance if the external temperature is 14°C and humidity 80%, as a rough calculation, the external dew point is about 14-(100-80)/5 = 10°C.
Evidence & Illustrations
Mould is growing near the external walls. Mould growth occurs where relative humidity exceeds 85%RH for more than six hours. Excessive humidity is usually due to insufficient ventilation, poor air circulation, and cold surfaces.
I understand that the extractor fan has only just been installed. This would account for about 1/2L of water vapour for every shower, and slightly less for baths. But I also understand that this bathroom is rarely used.
The heat loss causes condensation, when the temperature drops below the dew point.
To keep the property dry | |
|---|---|
| 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). | £180 |
| 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. In addition monitor improvements on the damp wall a pencil line and damp meter such as dr.wood moisture meter, logging improvements each month. 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. In addition monitor improvements on the damp wall with a pencil line and damp meter such as dr.wood moisture meter, logging improvements each month. | |
| keep some late night heat | |
| TIP: Maintain a small amount of heat 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. | |
| Use fan to expedite drying | |
| Direct a fan onto the leak to speed up the drying process. | |
| 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, such as the annex. | |
| 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 cooking with an extractor fan | |
| Consider installing a kitchen extractor fan, ducted out. | |
| 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. | |
| Push back the lead flashing to prevent water splashing from the gutter. | |
| This needs a ladder, but only takes a few minutes. I would gently move back the lead by about 1cm (not too far as you still want rain to drip into the gutter). Make sure to clear the gutters of debris while up there. | £200 |
| Reposition and secure the outside drain to prevent drips. | |
| Adjust the rainwater drain to the front. This could be your neighbours’ responsibility. | £100 |
| Remedial actions – estimate of costs | £480 |
Actions if all else fails | |
|---|---|
| Consider installing ducting behind bathroom fan | |
| The ground floor bathroom vent ducting should have a rigid duct, failing that use a flexible duct pulled about 90% taught to improve airflow. | £100 |
| Consider installing a bathroom extractor fan with 30 minute overrun after lights are switched off. | |
| Consider installing a bathroom to the first floor bathroom. With at least a 30 minute overrun. | £500 |
| repair render cracks | |
| It is not urgent, but consider repairing render cracks. | |
| Repair or replace the kitchen extractor fan. | |
| Consider repairing or replacing the current kitchen extractor fan, it appears to be suitable ducted out, although I could not check it, which is something you can do with an anemometer outside, once it is functioning. | £500 |
| Consider targeted insulation | |
| Consider insulating the atrium, such with internal thermal lining paper or thermal insulating plasterboard. | |
| Inspect gutters and rainwater goods semi-annually. | |
| Paint external woodwork | |
| £Paint woodwork, such as the atrium to protect it against window rot. | |
| 200 | |
| Optimal actions – estimate of costs | £1,100 |
I conclude that the primary cause of damp is condensation from excess vapour, notably in the kitchen, from drying clothes, and the bathroom..
Condensation forming on a cold wall can mimic a leak or rising damp, but the root cause is condensation, not rising damp. Rising damp is defined as the upward movement of groundwater, which is the water beneath the water table. All forms of damp will appear to rise through absorption including condensation. The downstairs bathroom fan is working OK now, but should have duct out of the void behind it. There is no upstairs bathroom extractor fan. The kitchen extractor fan is not working. Vapour is not removed form drying clothes.
Improved the extraction rate of the bathroom extractor fan by about 400%. I moved the dripping water butt overflow pipe.. By taking a root cause approach, rather than a focus on blocking the symptoms of damp the savings are likely to be around £6,000. 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: Near low productive aquifer with intergranular flow See British Geological Survey.
Therefore risk of Rising Damphighly unlikely, see explanation by Dr Robyn Pender of Historic England.
I confirm that I inspected the property on 231025SH1000. I conclude that the primary cause of damp is condensation from excess vapour, notably in the kitchen, from drying clothes, and the bathroom.. 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 231025SH1000
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.
- Weather:Cloudy, 13°C, 95% relative humidity.
- :The building, originally a laundry, was converted into two houses around the 1850s, capitalising on the rapid railway service to London’s prestigious hotels.
- :The property was purchased during the Covid pandemic. Issues emerged soon after the roof, much of which had to be replaced, but problems persist under the roof, on the ground floor, and in the atrium.
- :The property was transformed into a residential space with a very open plan. Kitchen extractor fan ceased functioning, and solid floors were noted, with some fans not operating effectively.
- :A couple occupies a large space.
- :Mould seen on some cold external walls
- :Dampness at the base of walls, particularly in the kitchen area and along the corridor. Owners suspect the cause is rising damp.
- :Dampness under the roof and in the atrium.
- :Inadequate kitchen ventilation and reduced heating, especially in the atrium. Drying clothes internally.
- :Not necessary due to solid flooring.
- :Not applicable due to solid flooring.
- :house from split building
- :a semi-detached
- :Victorian
- :9 inches thick.
- :Some buddleia growing under what seems to be a damaged or overflowing gutter, potentially historic. A Water butt overflow pipe is dripping as was a rainwater drain to the front.
- :Walls are dry lined, hiding penetrating damp issues.
- :No concerns with drains.
- :No concerns with mains water or wastewater.
- :There are no obvious signs of a significant mains or wastewater leak.
- :Solid floor.
- :The loft is open
- :There are no suspicions of significant timber decay.
- :The property was reportedly dry when purchased during the Covid pandemic.
- :The downstairs bathroom fan is working OK now, but should have duct out of the void behind it. There is no upstairs bathroom extractor fan. The kitchen extractor fan is not working. Vapour is not removed form drying clothes.
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 (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.
RICS, PCA, HISTORIC ENGLAND JPS REPORT
RICS (Royal Institute of Chartered Surveyors), Historic England (a public trust protecting sites of historic interest) and the Property Care Association (an association of mainly damp proofers) set out a Joint Position Statement (JPS), in September 2022 – see below.There has long been disagreement about the causes of damp amongst surveyors. Historic England surveyors represent one extreme. They typically do not believe rising damp is a likely cause of internal dampness and rarely recommend altering walls to alleviate damp. By contrast PCA surveyors typically recommend rising damp treatment whenever they see dampness at the base of a wall and often recommend altering a building. RICS surveyors tend to be somewhere near the centre of these extremes. However, unlike Historic England and PCA surveyors, they rarely specialise in damp and often refer issues to PCA surveyors. We and most other independent surveyors are more closely aligned with Historic England’s position except that we are perhaps more pragmatic. For example, if a hole in the wall is the optimum way of solving internal dampness, then we will recommend it, but not otherwise.
JPS questions and answers
In addition to the content typically included in a professional and impartial survey report (e.g. client, surveyor and property details; limitations and exclusions), the report should include the following information:1 A summary of the surveyor’s observations, including an Assessment of Significance.
Dampness at the base of the wall, resembling rising damp, but caused by condensation on a solid floor.
2 The importance of regular building maintenance and how a lack of even basic maintenance can lead to problems arising. This is especially important and relevant to roofs, gutters, hidden gutters, rainwater disposal and changes in external ground levels.
As is common with all buildings, gutters and other rainwater goods should be checked twice annually, ideally during or soon after a rainstorm, for evidence of overflow and rain not being dispersed properly from the property. You should also check that there is no flow of water flow during periods of absence for signs of a leak, for instance, by note the number on the mains water meter outside your house. Gutters need inspection during a rainstorm. The ground is slightly elevated but does not seem to be causing internal dampness.
3 An impartial diagnosis of the damp problem, which should be clearly explained and laid out systematically to communicate the relevant risks to the reader.
Condensation is the primary cause of damp. There are no significant risks other than damage to internal walls.
4 Where recommendations for the repair and recovery of moisture-affected structures are stated, the solutions should be clearly explained and prioritised as appropriate.
The solutions are explained in the Recommendations section. The primary recommendation is Use a dehumidifier capable of extracting 20 litres per day, repair the kitchen extractor fan, and monitor internal humidity, aiming to keep the dew point as low as the external dew point.
5 The client should be provided with alternative options for which each recommendation should include advantages and disadvantages and the relevant cost and time implications.
This question is primarily directed at PCA damp proofers, to encourage them to consider methods that address the source of water not just the symptoms, such as by hacking off plaster and replacing it with slurry. You can sometimes take this damp proofing approach with short-term success. However, water will eventually find its way through. Furthermore, treatment is disruptive resulting in high cost and a poor finish, with no worthwhile guarantee of success. It likely to lower the value of the property. In our opinion you are better off trying to stop the water at its source, as we recommend. ” No alternatives required or appropriate.
6 Where monitoring and staged interventions are appropriate or beneficial, the client should be informed of the reasons for these options, together with the likely cost and time implications of such recovery strategies.
Properties should be monitored for humidity and temperature using data loggers, see datalogger section of this report. The cost of data loggers is currently less than £20 for two, aim to keep the dew point, as shown on the app screen of each logger (bottom centre on the SensorBlue), within 3°C of the external temperature, especially at night (use ventilation and/or dehumidification to reduce the internal dew point – measure external conditions or refer to weather forecasts for night-time temperatures, such as BBC Weather – a short explanation is; that this will make sure the relative humidity of all surfaces will be below the mould point even if poorly insulated). We also suggest noting values monthly using a multi-functional radio wave and conductance damp meter costing about £24 to monitor and map damp patches on internal walls. This way you can monitoring the dry progress, which typically takes 1 month per 25mm thickness of walls and more if coated. This helps determine if the root cause has been fixed or there is an additional or new source of water, and therefore more actions are required. Ideally this should be started before or soon after starting our recommendations and for about a year, repeating monthly to check progress. Monitor visually and with a radio damp meter and data loggers, see recommendations.
7 Where appropriate, clearly state whether the building concerned represents a financial risk to the buyer or lender and why.
8 Any conflicts of interest should be clearly stated.
There is no conflict of interest. We never profit from our recommendations.
As a background, although we charge a fee for undertaking damp surveys, profit is not our primary motivator. We are motivated to:
- solve damp problems in properties,
- encourage clients to spend money wisely for the protection of the property and, where possible to lower the environmental impact,
- stop or at least play our part to reduce the over-diagnosis of rising damp and so called “damp proofing” treatment by replacing plaster with chemicals and slurry, rather than dealing with the root cause.
Relevant examples of similar damp issues or remediation:
To Be Revisited.
[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?