Data loggers
In conclusion, from the data loggers
- Fantastic, this is a perfect example of mould risk before the survey and no mould risk after the survey.
- During the period under investigation the surface relative humidity on the damp wall (green line) is above the mould risk of 85%RH up to 26 October. The average drops from about 87%RH initially to about 83%RH taking it marginally out of the mould risk zone. Then from 30 October the average surface relative humidity drop to an average of about 67%RH when I presume you started running a dehumidifier.
- The grey line is the dew point differential. It shows me that vapour is coming from the bathroom relative to the second bedroom, as you would expect. The increase in differential after the survey tells me that the door is being kept closed, this stop vapour diffusing into other rooms and helps reduce the mould and condensation on cold walls.
- The example property’s dew point is, in fact, from my house, where I run a dehumidifier. Although I am missing my data from 4 November, I can see you are dropping below my and external dew points, which can only be done with a dehumidifier.
- It is important to note that this second bedroom it kept cold, 1 – 2°C colder than the bathroom, which is probably 1 – 2°C colder than the rest of the property. The surface temperature of the mouldy wall is a further 2°C colder than the bedroom temperature. It is this low temperature that is causing the high surface relative humidity, resulting in mould and condensation.
- The internal dew point is similar to the external dew point, only occasionally higher, suggesting that the ventilation is adequate. This illustrates that ventilation replaces internal vapour with external vapour, so there soon comes a point of diminishing return. Yet the surface relative humidity can be high when cold, this makes sense when you consider that rain occurs when temperature drops below the dew point. The only solution to dropping vapour quantity is to use a dehumidifier.
- The only way to keep the wall condensation or mould free is with insulation (to increase wall temperature), heat or a dehumidifier. Of all those options, dehumidifier is the cheapest solution and one of the environmental solutions, as low humidity feels warmer therefore less heat is needed (until about 70%RH).
- Overall the graph demonstrates success.
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 growth is inhibited by nitrates found in groundwater. The presence of mould at the bottom of a wall rules out rising damp as the root cause and points towards condensation from unvented excess vapour.
There was a time when surveyors used to recommend removing the lower sections of render to expose the brick wall. Unfortunately this increases heat loss and there risks of condensation, through concentrated rainwater absorbed into the base of the wall.
To keep the property dry | |
|---|---|
| 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 | |
| Cook with tops on pots and pans, turn the heat down to a simmer and or use the kitchen extractor fan. | |
| 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 |
| Use fan to expedite drying | |
| Direct a fan onto the damp wall to speed up the drying process. | |
| 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). | |
| 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 |
| Fill render crack | |
| Check and repair any cracks in the exterior walls to prevent water ingress. Address external render cracks by raking out, that is slightly enlarging and removing loose material and filling with an acrylic based caulk for small gaps and cement based mortar for larger gaps over 3mm. | £100 |
| Remedial actions – estimate of costs | £380 |
Actions if all else fails | |
|---|---|
| Consider insulating external gas pipes | |
| Consider running insulation along the gas pipes, check with British Gas to make sure it is not against their policy. | £50 |
| Consider installing thermal insulation to exterior of flank wall (or any other cold wall) – in the region of £100 per sq. m. + scaffolding. | |
| This may be unnecessary if you rarely use the room. | £1,000 |
| Optimal actions – estimate of costs | £1,050 |
I conclude that the primary cause of damp in this property is excess humidity, leading to condensation along a cold section of the wall in a poorly heated or insulated room..
The heat loss increases the surface relative humidity to a point where mould can grow.
Improved the bathroom extractor fan by cleaning it out and unblocked a drain.. 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: Risk of surface water (i.e. penetrating damp from rainwater, not rising damp from groundwater) See Flood Risk (note most flood risk is not from groundwater).
Sub-soil rocks: Rocks with essentially no groundwater 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 231026SH0800. I conclude that the primary cause of damp in this property is excess humidity, leading to condensation along a cold section of the wall in a poorly heated or insulated room.. 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 231026SH0800
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.
- Rising damp concern: You were concern you might have rising damp.
- Damp treatment: Dutch method. Despite the low risk of rising damp, there has been an attempt at a treatment against rising damp. Rising damp treatment is normally a sign of insufficient ventilation. The wall have been treated using the “Dutch” or Frank Schrijver method, whereby holes about 1 brick deep and 50mm wide are cut into the wall. The theory being that dampness in the brick will evaporate out. The side effect of this approach is reduced insulation increasing the risk of internal condensation. To reduce the risk of condensation on the inside of the treated walls, the normal absorbent plaster is replaced with damp proofers impermeable plaster (“slurry”). This can cause problems with absorption imbalance, resulting in increased condensation on other walls or vapour becoming absorbed and trapped behind the slurry. There was evidence of surface condensation in areas probably not treated with replacement plaster but no evidence of trapped vapour. The solution is through ventilation and humidity control.
- Weather: Cloudy with intermittent sun, 11°C and 89% relative humidity.
- Property: The property is a ground floor flat in a large semi-detached Victorian building.
- Background: The owner recently acquired the freehold.
- Changes: The house was divided into flats. A recent gas line installation along a flank wall. The wall has been rendered but damp proofed, with the Dutch system and leaving a gap at the base with exposed brickwork.
- Occupancy: Low occupancy.
- Mould & notes: The room with damp and mould issues is typically unheated, with the radiator positioned away from the affected wall.
- Primary damp concern: Mould and dampness along the flank wall.
- Other damp concerns: None.
- Compounding: Heat loss at the base of the wall, likely from the new gas line installation, exacerbated by water ingress from rain and a blocked drain.
- Airbricks: There appear to be sufficient airbricks.
- Sub-floor humidity: No concerns with sub-floor relative humidity.
- Tenure: ground floor flat
- Attachment: a semi-detached
- Build: Victorian
- Walls: 9 inches thick.
- Exterior comment: Signs of render cracks and slight damage to the rainwater goods at the rear.
- Penetrating damp assessment: The exterior appeared to be OK from a damp perspective. There are no obvious signs of significant penetrating damp.
- Drains: One of the drains was blocked, which I unblocked during the survey.
- Leak signs: No signs of a mains water leak.
- Leak assessment: There are no obvious signs of a significant mains or wastewater leak.
- Floor: Suspended timber floor.
- Loft: There was no loft.
- Timber assessment: There are no suspicions of significant timber decay.
- Last dry: The property was last dry prior to Covid.
- Ventilation assessment: The fan extractor fan is not running sufficiently fast and the overrun is not 30 minutes as it should be.
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.
Mould and condensation at the base of the wall.
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. Exterior maintenance required; no specific ground level issues.
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.
The diagnosis is condensation; there are no specific ongoing risks other than mould, which should be wiped away
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 Remove mould with anti-mould spray, use a dehumidifier in the bedroom, especially if maintaining different heating regimes. Ensure the bathroom door remains closed for at least half an hour after showering and keep the extractor fan running. Additionally, when drying clothes indoors, use a dehumidifier and ensure cooking vapour is extracted.
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. ” 5 alternative options
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 Filled In Later.
[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?