Data loggers
In conclusion from the data loggers
- During the period under investigation the surface relative humidity on the mouldy wall (green line) is high, peaking at 100%RH and risking condensation on the coldest surfaces. Relative humidity is often 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 while some vapour is coming from the bathroom, most of the vapour is coming from the bedroom relative to the bathroom.
- It is interesting to see what happens when the property is empty. The family had a weekend away from 13 to 16th October. While there was a steady decline in external dew point and in the bathroom, this was not the case in the bedroom. Likewise the property was kept warm, which is great, but it would have been more efficient to use a dehumidifier. The lower external temperatures would have increased the surface relative humidity and therefore mould risk.
- 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 excess vapour causing condensation and mould, 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 ore efficient use of the dehumidifier.
- The relative humidity is a measure of how much vapour is in the air compared to air’s capacity to hold vapour. 100% is called the dew point. It is where air cannot hold any more vapour, resulting in condensation. Above 85%RH for long periods of 6 or more hours risks mould. You have to remember that the data logger won’t measure the temperature of the coldest section of wall. Roughly, for every 1°C decrease in temperature increases relative humidity by about 5%RH.
- The dew point is the temperature where the air around the sensor will start to condense. In this case 18.3°C, which is exceptionally high. It is likely that the surface temperature of some of the walls were below 18.3°C.
- The dew point in the bathroom is lower. Dew point is a proxy for vapour quantity, so when comparing one room to another we can say there is more vapourin the bedroom compared to the bathroom, despite a recent shower. I believe part of the reason is that the bathroom door is left open, which it should not be, as you want as much high concentration vapour to be targeted and removed by the bathroom extractor fan.
- VPD is the vapour pressure deficit. Effectively the opposite of dew points, it tells us how much more vapour can be held in air.
- High and low shows that the temperature has been 26°C on the bathroom ledge. Modern showers pour hot water high speed creating considerably more steam than was historically the case. So ventilation needs to be targeted.
- Normally the sensors have batteries that can last 1 year, but they can only store about 980 – 100 days worth of data. So need to be reset every so often, either within the app by pressing the logger’s name within the app then go down to count up and press “Sending restart Command” or by briefly taking the batteries out.
Evidence & Illustrations
Chimneys are made from a single brick enclosing a void, this can cause slight heat loss. 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.
Relative humidity measures the amount of vapour in the air relative to the air’s capacity to hold vapour. It is influenced by vapour pressure and temperature. As temperature rises, the air can hold more vapour. Conversely, as temperature drops, the air’s capacity to hold vapour decreases until it reaches the dew point at 100%RH, resulting in the formation of dew or condensation.
A secondary cause of high relative humidity is a low temperature relative to the source of humidity.
Unsurprisingly the wall has clutter reducing the airflow. Vapour moves through diffusion, whereas warm air moves mainly through air currents. Clutters increases surface relative humidity and the risk of mould.
Active vents, i.e. electrical are better than passive vents. Either seal it up with insulation or keep it open.
To keep the property dry | |
|---|---|
| Ask tenants to remove 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. | |
| Ask tenants to remove vapour from clothes drying | |
| Ask tenants to use the dehumidifier provided in the room where clothes are drying, with the door closed, make sure to decant the dehumidifier daily. | |
| Ask tenants to remove vapour from cooking | |
| Cook with tops on pots and pans to reduce the production of vapour from cooking by 80%. | |
| 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). | |
| 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. | |
| Remove mould | |
| Consider sanding down mould where dry, and removing it with either bleach or anti-mould foam. I personally use HG Mould Remover Foam Spray, but imagine there is no major difference between brands. | £100 |
| Remedial actions – estimate of costs | £100 |
Actions if all else fails | |
|---|---|
| Target insulation | |
| I would insulate the wall where mould is growing for example with thermal insulated lining paper. | £200 |
| Optimal actions – estimate of costs | £200 |
I conclude that there was condensation and mould caused by insufficient ventilation and slight thermal imbalance.
The tenants are relying on a bathroom extractor fan which was not working sufficiently, now fixed. Clothes are dried internally without using the dehumidifier in the room where clothes are dried.
I fixed the bathroom extractor fan, increasing the timer length to 30 minutes and ask tenants to keep the bathroom door closed and used the dehumidifier when drying clothes.. 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 Dampremote possibility, see explanation by Dr Robyn Pender of Historic England.
I confirm that I inspected the property on 231019SH0800. I conclude that there was condensation and mould caused by insufficient ventilation and slight thermal imbalance. 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 231019SH0800
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: dry
- :Victorian ground floor flat
- :conversion into flats, central heating, double glazing and lifestyle changes including more frequent hot showers and clothes washing, including greater occupancy during the Covid pandemic.
- :tenant
- :mould seen in bedroom
- :mould and condensation in bedrooms
- :heat loss from around the chimney breast
- :There is no reason to be concerned about the sub-floor ventilation.
- :There were no concerns about humidity in the sub-floor void.
- :ground floor flat
- :a semi-detached
- :Victorian
- :solid wall made of two brick widths (225mm)
- :There were no major concerns seen externally that would account for internal issues.
- :The exterior appeared to be OK from a damp perspective. There are no obvious signs of significant penetrating damp.
- :The drains are of no special concern.
- :No suspicion of a mains water leak
- :There are no obvious signs of a significant mains or wastewater leak.
- :The floor is of no special concern.
- :There was no loft.
- :There are no suspicions of significant timber decay.
- :It is difficult to know when dampness started.
- :The bathroom extractor fan had a blocked backdraught shutter and short timer. I repaired both.
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.
Primary dampness is at base of the wall accompanied by mould.
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. There are no significant additional maintenance issues, but the bathroom extractor fan should e checked regularly for flow.
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.
Excess vapour. There is a risk of mould until the mould is remove with anti-mould spray and until humidity is brought down so that dew point matches outdoor dew point.
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 ventilation and dehumidifiers provided, as directed
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.
The property is not the subject of a sale. In our opinion, there is no material financial risk once you have followed our recommendations.
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.
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?