Background
A terraced Victorian townhouse, with damp across the basement.
Data loggers – see damp.ai/detect
Using A.I. I have created an automatic data logger analyser (in beta – the graph works well, the analysis needs more data) damp.ai/detect and in the calibration drop down use:
P1: +0.87°C -1.4%RH,
P2: -0.44°C +11.7%RH (the maximum recalibration on the sensor blue app is 9.9),
P3: -1.68°C +7%RH.
The main things to look for are:
- P1: relative humidity – consistent 50 – 65%RH is indicative of hygroscopic salts.
- P1, P3 dew points, there should always be below the external temperature, spikes above the external temperature suggest poor ventilation.
- P2’s relative dew points, indicates vapour coming from one room relative to another.
Evidence & Illustrations
Internal dampness is unwanted moisture. In the residential environment, the causes can be broken down into four sources, from least common to most common:
- Rising damp which comes from groundwater: typically it presence itself as high damp meter readings across the whole property and neighbouring property, with no rise into corners. Rising damp is very uncommon especially in cities where groundwater is pumped out. Fortunately it is easy to prove by drilling down 1M either side (avoiding cables and pipes) and seeing if free water is equally distributed. No water means no rising damp. Higher water on one side than another means a leaking pipe, which should be repaired to reduce the risk of subsidence and rot.
- Penetrating damp which comes from rainwater: typically see high up a wall, but can be the base of a wall, normally accompanied by a brown stain.
- Leaks or other source of mainswater: typically accompanied by a brown stain, often spreads wide across a solid floor.
- Condensation and mould from excess vapour causing: the most common cause in homes, accounting for about 85% of damp issues, typically colourless, but not always, sometimes with salts, found in cold reveals and at the cold base of a wall. If no other source is found, then dampness should be treated as coming from excess vapour by drying a damp wall with a fan and dehumidifier monitoring dampness in a wall. If the wall starts to dry within a few months, then you have probably solved the cause moisture. Either way maintain internal vapour, as measured by dew point, below the external temperature (Dews Law).
- Hygroscopic salts mainly originate from the historic burning of coal or animal excrement, but less commonly can be caused by groundwater. These salts cause deliquescence, a form of condensation. It is not a source of moisture, it is benign but dampness in walls in dynamic equilibrium – that is both evaporation and condensation. From my experience, historic burning of coal, reveals when a chimney has been replastered accounts for about 1/3 of dampness in summertime.
1. Rising damp – a whole industry has evolved to carry out rising damp treatment, when in large part it is rare and misdiagnosed (misdiagnosis costs the country about $1Billion). Any source of moisture will be absorbed upwards. So the term rising damp is restricted to dampness caused by groundwater, that is the water under the water table, not rainwater percolating through soil. In London, there are bore holes that pump water out to about 70M, so way too far below your house to be the root cause.
1, Holes in wall causes heat loss increasing the risk of condensation, the most common cause of internal dampness. 2, The holes eventually become clogged up, here will paint, presumably for decorative reasons.
3, Rising damp is rarely if ever the root causes, especially in London, so dampness continues.
I believe that this chimney has been damp proofed by replacing the plaster with impermeable, or water resistant plaster. While this is a valid method of damp-proofing, it is over engineered in my opinion. Hygroscopic salts can never be removed completely from the underlying brick wall, so the best way to deal with them is by covering. A simple method is to use an oil based primer, such as Zinsser Cover stain – at least 2 coats, covering whole section of wall, or at least 300mm overlap.
2. Leaks or similar from mainswater.
It is possible that water is coming from a drain, but all the drains appears to exit the building above the lower ground floor and therefore should not have an affect.
3. Penetrating damp from rainwater
4. Condensation from excess vapour
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.
4.b Hygroscopic salts – these are not a source of moisture, cause deliquescence, which is a form of condensation.
It is highly unusual to find mould and hygroscopic salts together, although I have replicated it. The main reason is that hygroscopic salts buffer humidity around the critical relative humidity. For Calcium nitrate the CRH is about 50%RH at room temperature. In this case, I believe something to do with the material backing the mirror, distance from the wall and bricks behind the wall has cause the buffering effect to be overwhelmed. I would guess that but for constant and intense cleaning, the house would be covered in mould and that condensation a major factor causing dampness in this property.
Other walls
I also note the kitchen fan is very noisy, so is probably rarely used and the condenser drying in the utility room feels humid near is suggesting a source of vapour. The property has been used for short term rentals. Occupiers are less likely to use dryers and extractor fans than owners, increasing the risk of condensation and mould.
Other matters
To keep the property dry | |
|---|---|
| Visit neighbour | |
| Ask neighbour on right-hand side about any damp they may have on the other side of the chimney breast. A leak should come from above and would typically cause staining on the ceiling and chimney breast on the other side of the wall. Clearly the leak has to be stopped and the wall dried out before coving the hygroscopic salts, otherwise vapour could blister behind the primer. | |
| Use fan to expedite drying | |
| Direct a fan onto the damp patch to speed up the drying process. | £50 |
| 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 a dehumidifier based on daily and tank capacity, low noise, whether it has a pipe out, and ease of programmable functions over other considerations such as weight and aesthetics. The technology is 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 |
| Follow Dew’s Law | |
| Follow Dew’s Law to effectively manage internal vapour, it is crucial to maintain the internal vapour levels, as measured by the dew point in degrees Centigrade, below the external temperature. This can be achieved through adequate ventilation and the use of dehumidifiers. Monitor the internal Dew Point with a reliable device, such as the Habotest Hygrometer or Dew Point Meter HT607, or utilise the sensorblue app paired with the ORIA Wireless Thermometer Hygrometer. These tools help in accurately gauging humidity levels, ensuring they remain optimal. For more detailed information on detecting and managing damp issues, please visit https://damp.ai/detect. | |
| 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 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, be aware that some condenser dryers release vapour, so monitor vapour, as dew point and use a dehumidifier to remove excess vapour. | |
| Reduce vapour from cooking | |
| Cook with tops on pots and pans to reduce the production of vapour from cooking by 80%. | |
| Repaint external walls | |
| Wire brush the paint on the external walls back to brick, as much as possible at least to remove the surface salts. Then use a paint that is as impermeable, ideally the same as the existing paint, or more impermeable, such as Zinsser or Dulux external masonry paint. | £1,000 |
| Remedial actions – estimate of costs | £1,230 |
Actions if all else fails | |
|---|---|
| Bathroom extractor fan | |
| Consider installing a continuous flow bathroom extractor fan such as Vent-Axia Extractor Fan With Humidistat & Timer Continuous Running and Timer, or Brookvent Airstream DMEV 100 HT (Continuous Running Extractor Fan with Humidistat Timer). | £600 |
| Consider installing a kitchen extractor | |
| Ideally, kitchens should feature a quiet, user-friendly extractor fan strategically placed right above or adjacent to boiling pots and pans, ensuring vapour is efficiently expelled outdoors. Unfortunately, some installers overlook the necessity of outdoor ducting, effectively nullifying the fan’s purpose, or they opt for lengthy, flexible ducting that’s susceptible to damage and hampers airflow with its ridges and bends. To maximize the likelihood of its use, the fan’s noise level and ease of operation are crucial factors. A fan that operates quietly and automatically is more likely to be used consistently, enhancing kitchen ventilation and comfort. | £1,000 |
| Hygroscopic salts | |
| Hygroscopic salts may resemble grease stains but rest assured, they’re harmless. They don’t cause damage, yet can appear unsightly, especially during summer heatwaves, potentially complicating property sales or rentals. Keep this report handy to reassure prospective buyers of their benign nature. Effective Solutions: The prime method to conceal these salts involves an impermeable blocker with at least 300mm overlap, preventing the spread of any damp appearance. Aim for a uniform treatment across wall sections to ensure consistent humidity interaction. Remember, these salts often lurk just below the surface. Cost-Effective Remediation Methods: Zinsser Cover Stain: The simplest, most affordable approach. Two coats of this solvent-based primer-sealer should do the trick, costing about £15 plus potential labour. It’s user-friendly, easy to remove and reapply, making it ideal for DIY fixes. For larger areas, consider a gloss paint layer between two Zinsser coats for uniformity. This is a homeowner-friendly task but can also be efficiently tackled by a builder as part of a bigger project. Sempatap/Wallrock: Ideal for mildly cold walls, this lining paper creates a barrier, offering slight insulation. It’s a half-day job costing about £100 per linear metre. Thermal Insulating Plasterboard: For very cold walls, removing plaster and installing this board with a vapour barrier is best, mirroring professional damp proofing. It’s a day-long task, costing around £400 per linear metre. Note on Damp Proofing Slurry: Often less effective, as it can activate salts, it’s also invasive and costly. Starting Point: Zinsser Cover Stain is your go-to. It’s budget-friendly and effective for immediate action, with the option to escalate to plasterboard installation if necessary. Humidity Management: Excessive humidity can highlight salts at the impermeable material’s edge. If this happens, a second Zinsser application is recommended. | £200 |
| Optimal actions – estimate of costs | £1,800 |
I conclude that the primary cause of the main damp issue is almost certainly hygroscopic salts and excess vapour. It is unlikely, but I can’t exclude a leak from the neighbour’s side.
The dampness on the wall looks like it comes from hygroscopic salts. The mould behind the mirror is highly unusual. It suggests that, but for regular deep cleaning, the house would be mouldy, and that excess vapour is a significant factor.
. By taking a root cause approach, rather than a focus on blocking the symptoms of damp the savings are likely to be around £30,000. This contrasts with typical damp proofing contractor recommendations such as chemical treatment for rising damp and untargeted ventilation, such as PIV systems.
Flood risk: No risk See Flood Risk (note most flood risk is not from groundwater).
Sub-soil rocks: Rocks with essentially no groundwater See British Geological Survey.
Therefore risk of Rising Damp: remote possibility, see explanation by Dr Robyn Pender of Historic England.
I confirm that I inspected the property on 240808SH1200. I conclude that the primary cause of the main damp issue is almost certainly hygroscopic salts and excess vapour. it is unlikely, but i can’t exclude a leak from the neighbour’s side.. 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 240808SH1200
Simon Hichens BSc Chemistry RICS Qualified Expert Witness (Chartered Surveyors)
PCA Certificated Surveyor of Dampness & Timber in Buildings (Property Care Association)
Damp Surveys Ltd, 119 Longton Ave London SE26 6RF Reg. 10977488 (England & Wales)
Founder of damp.aï & Member of the Society for the Protection of Ancient Buildings (SPAB)
Our damp surveys are designed to provide a holistic diagnosis that identifies and deals with causes rather than a focus on symptoms. Symptoms will disappear over time, once damp is stopped at source. We look for risks of dampness, but unless moisture is present, we can’t guarantee to identify all risks of future moisture. Our reports:
- identify root cause(s) of major unwanted dampness within the property,
- identify major symptoms of unwanted dampness,
- identify major structural damage caused by dampness,
- recommend actions and estimated costs to stop damp at source and mitigate its effects,
- recognise that treating damp is often a staged approach, treating obvious causes first.
Understanding damp
For survey purposes, damp is defined as unwanted water. Water brings life. We need it. Unfortunately, fungus and insects also thrive in water. While a damp wall can cause decorative spoiling, it is not moisture, but the life it brings that causes the greatest concern in the home environment. FACT: vapour causes 85% of residential damp problems.
Independence and Methodology
Our only income is through damp survey fees. We are independent of contractors and never profit from remedial work. We do not receive or pay any fees or other inducements. Our motivation is peace of mind and practical, durable solutions. We use an array of equipment to identify the root cause of damp within walls. Our damp surveys follow guidance from RICS, Historic England and PCA joint position statement and support RICS’s highest standard, level 3 “Home Survey Standard” (HSS).
During the survey we assess likelihood of rising damp*, mainswater leak, penetrating damp, condensation, timber rot and woodworm. We profile the damp patches and consider the likely sources of dampness and test ventilation against building regulations requirements. We consider changes to the property and factors just before the first sighting of damp.
“Management of moisture requires proper control of temperature and ventilation to avoid excess humidity, condensation on surfaces and excess moisture in materials. Ventilation should be distributed effectively throughout spaces, and stagnant air zones should be avoided.”
FACT: Houses contain 30 – 40 litres of water as vapour typically. Each day, each occupant adds on average about 1.5 litres as follows:
- Each shower results in 1/2L condensing (each additional shower in a series won’t add as much as the first, so long as the door is kept closed)
- Vapour from drying clothes releases about ½ litre per day if dried indoors
- Respiration releases about ¾ litre per day (of which ¼ l at night)
- Cooking produces about ¼ litre per day per person
- Unvented vapour can cause condensation, mould and allergenic dust mites. The simple rule for keeping your property dry and mould free is;
- Vent out as much vapour as produced, each and every day!
- Central heating and double-glazing reduce background ventilation. To overcome this you should use mechanical extractors. Where properties are rented, consider using monitoring devices (such as a Govee WIFI hygrometer) and if necessary, install continuous flow extractors, but beware there can be a thermal cost caused by continuous heat lost.
FACTS about Condensation and Mould
- FACT: warm air holds more water vapour than cold air. The warmer it is, the more air’s capacity to hold water vapour. Conversely the colder it is, the less capacity, until air cannot hold any more vapour. We call that the dew point or 100%RH. As soon air reaches capacity, condensation will form on the coldest surfaces.
- FACT: Mould and dust mites
- FACT: Mould only grows when air is humid for long periods. In the occupied home environment, it is 6 hours over 85% RH. For properties that are unoccupied for long periods, it is 75% RH for many days of consistent and high humidity. Avoid allowing the surface relative humidity of cold walls to exceed 85% RH by ventilating, dehumidifying, insulating, and ensuring airflow, particularly in cold corners, base of walls and ceilings, eaves, and cold window and door reveals.
- FACT: Dust mites are microscopic insects that can cause allergies. They grow in similar conditions to mould. So ventilate more to avoid allergies.
- FACT: Health concerns: There are no health and safety issues from damp noted. It is in the occupier’s interests to keep a property properly ventilated or dehumidified and temperatures above the dew and mould points throughout the property, thereby reducing the health risk associated with dust mites, bacteria, protozoans, as well as decorative spoiling caused by mould.
TIPS To Stay Condensation and Mould Free
- TIP: Reduce the production of vapour at source:
- TIP: Keep bathroom extractor fans running, or window open for at least 30 minutes.
- TIP: Keep bathroom doors closed at all times, and bathroom windows open safely.
- TIP: When filling the bath, run the cold water first then add the hot.
- TIP: Dry clothes outside, in a dryer, in a closed room with a dehumidifier or window open, never on radiators or heated rail without a door closed and a means of removing the vapour.
- TIP: Cook with tops on pots and pans, avoiding excessive boiling.
- TIP: Keep the kitchen door closed and extractor fan on where possible.
- TIP:Mechanical vents are best, but if you only have passive vents, such as a whole in the wall or chimney, then vents open with space for air to move, insulate where possible.
- TIP: Keep trickle vents open or alternatively, open windows on safety locks.
- TIP: Stop mould forming:
* Maintain external wall temperatures above 12°C, with low background heating.
* Declutter leaving space for warm air to circulate around cold surfaces.
* Where possible, avoid placing wardrobes and furniture against external walls.
* Avoid overfilling wardrobes and cupboards as it restricts air circulation.
* Use dehumidifiers or small wardrobe dehumidifying bags and replace regularly.
* Wipe mould and condensation off walls and clothes as soon as it appears. - TIP: Monitor relative humidity
* We recommend monitoring temperature and relative humidity with a data logger to see what is happening.
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?