Mains water leak treated as if it were rising damp

Background

A lower ground Victorian flat has ongoing damp issues, despite the installation of rising damp treatments, including damp-proofing on external walls. Dampness is worsening at the alcove wall and floor corner joint in an external bedroom, particularly after rain, and the concrete sub-floor, which replaced the original wooden floorboards and cavity, shows signs of moisture. The rising damp treatment has not resolved the issue, and uncertainty remains about whether an appropriate damp-proof membrane (DPM) was applied under the concrete floors. The damp persists, and without understanding the root cause, any recommended treatment could be ineffective.

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Data loggers – see damp.ai/detect

The surface relative humidity reaches 100%RH at times, like early morning of 26th and 29th October. Both these occasions were when the external conditions were cold and high humidity, but not raining. The grey line at the base of the graph, shows the dew point differential, comparing the bedroom vapour levels to the bathroom. The bathroom clears of vapour quickly, showing that the extractor fan is working well. However, on the flip-side, the bedroom has excessively high levels of vapour. This is unlikely to come from rain, which at most would release about the same vapour as a damp T-shirt.

Conclusion from data loggers

Follow Dews Law by keeping internal vapour, as measured in °C by the dew point, below the outside temperature, day and night – see recommendations.

Evidence & Illustrations

The primary concern is dampness in the rear corner of the bedroom, next to the party wall. The outside skin of wall has been dry-lined, which is a method by which plasterboard is attached to a wall to reduce the risk of moisture passing through – it could be thought of as a form of damp proofing. Thermal insulating plasterboard would be more appropriate in this case as there is solid floor with no risk to structural timber.

The floor has been replaced with a solid floor, suggesting that the flat has suffered from rot in the past. There is mould in the corner and on the floor. Mould growth occurs where relative humidityexceeds 85%RH for more than six hours. Excessive humidity is usually due to insufficient ventilation, poor air circulation, and cold surfaces. 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.

The thermal lens, where blue is about 5°C colder than yellow, highlights areas of heat loss. There is significant heat loss in the corner of the room.

Looking outside the ground has been partially excavated, to the extent that you can feel the underside of brick behind the plinth. While it is possible that rainwater is penetrating through. If this were the case you would expect to see brown stains on the wall. Furthermore, it is unlikely that the damp seen inside that coincides with times of rain, is in fact caused by rain. If it were there would have to be water moving through a gap, rather than being absorbed through pores. It is far more likely that the water you are seeing is condensation. When it is rain the external vapourlevels are considerably higher, making extractor fan less efficient and dramatically increasing the risk of condensation.

The base of the wall should be insulated, for example with expanding foam, covered by a cement base render and ideally drained with a concrete patio displacing water away from the property.

I did not have a good look at the neighbour’s side. However, I could tell that it is about 1 or 2 course of bricks higher. This means that the base of you floor will be lower and therefore it will be colder and more prone to condensation.

It is important to mention that fish tanks, especially warm water tanks cause considerable condensation. All the water used to top up the tank is replacing water that has evaporate and condensed, probably on the coldest part of the room.

This a section of the illustration by Aquarend in 2020, which carried out remedial works, to damp proof the broiling against rising damp. The red number are presumably From a two pin conductance Protimeter in units of WRE (Wood Moisture Equivalence). 250 is considered damp, but the meter will flash at 200 WRE or above. 999 WRE normally means saturated. I assume the red number refer to damp meter readings at the wall base and green about 1 meter up the wall. Essentially the corner of the bedroom appears to be have been dry before the damp proofingtreatment – certainly dryer than it is now. There is dampness in the bathroom, where “pooling water” and “boiler overflow” have been noted.

Damp proofing treatment is theoretically to stop rising damp. Rising damp comes from groundwater, which is pumped out in London, so highly unlikely to be the root cause. The Sika Waterproofing render is used to hide damp, rather than to treat the root cause of the damp.

There is mould and rust, but no brown stain from penetrating damp, to the front of the build. This tells me that excess vapour is general, not just specific to the bedroom.

The cracks in the plaster along the party are a sign of past damp proofing treatment against rising damp. The wall is damp, as measured by a damp meter in radio frequency mode, which uses radio wave that pass up to about 70mm into a masonry wall. This suggests that there is and probably, was another source of water.

I tested and found a leak on your mains water system. There can be innocent explanations, such as leaking shower heads, cistern, taps etc. I could find none, so I suspect you have a leak and have had one for a very long time, explaining the rotten timber floor that needed replacement and past damp proofing treatment. It would be expensive to dig up the concrete to replace the pipe. But what you could do is bypass the old pipe with a new mainswater pipe, perhaps embedding it in the wall behind insulation and the skirting board. My gut feeling is that given the pipe will be under the solid floor, and therefore water will be drawn down, it is unlikely to have had an impact on the damp of primary concern, i.e. the damp in the bedroom corner, which I believe is caused by condensation. There will be a cost. 1 litre per hour costs about £27 per year. On that basis it could be worth following my main recommendations before considering the cost of bypassing the mains water pipe.

To keep the property dry
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.
Move or cover fish tank
The heated fish tank generates about two teaspoons of water every day. Although this may not seem significant compared to the two litres of water vapour produced daily by the average adult, it can contribute considerably to the overall humidity in the room, especially when combined with respiration at night. To mitigate this, I recommend slightly cracking open the window at night to improve ventilation.
Use a dehumidifier
Maintain relative humidity, especially at night when it’s cold outside, with a dehumidifier such as the PureMate 20L/Day Portable & Compact Dehumidifier with a 6.5-litre tank (£179.99, refrigerant), the Duux Bora Smart Dehumidifier (DXDH02UK, £300, refrigerant), or the 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 well-established and easy to manufacture with a similar function and fire risk profile to fridges. 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). I use a dehumidifier whenever leaving a property vacant, dripping into a sink, set to 70%RH, especially in winter – it is more efficient than other humidity managing methods including ventilation.	£180
Fill gap under outside wall
Insulate under the bedroom rear wall, and cover in a cement base mortar or render. Ideally drain with an Aco drain, or at least displace rainwater away from the property, such as with concrete patio sloping away from the building.	£800
Bathroom Humidity Management
After showering, keep the bathroom door closed and the window open or fan running for at least 30 minutes to allow vapour to dissipate.
Reduce vapour from cooking
Cook with tops on pots and pans to reduce the production of vapour from cooking by 80%.
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.
Remedial actions – estimate of costs	£980

This estimate is based on approximate time, costs and competence to complete repairs. It is not a quote for work. We are independent. A general builder can complete most work. trustedtraders.which.co.uk is good sources of general builders. Once the recommended remedial actions are completed and the walls allowed to dry, dampness will not have a material impact on the value of the property. It is the client’s responsibility to check that a contractor has sufficient insurance and competence to undertake any work that we recommend.

Actions if all else fails
Solutions for leak
First, ask a plumber to double-check that there is indeed a leak. Then, consider either locating and repairing the leak or bypassing it. One option is to embed a new mains water pipe in the wall behind the skirting board. Make sure to insulate the pipe to prevent condensation, especially when it becomes cold in the winter. Leak detection companies are a fairly mixed bag, some with a background as unsuccessful damp proofers. One of the few that has done a good job for a client is De-Yany Leak Detection Specialists, 17 Pevensey Avenue N11 2RB Email: LALeakdetection@gmail.com, 07886 702094. I have no connection. Alternatively use a company like Leakbusters.net.	£2,000
Optimal actions – estimate of costs	£2,000

I conclude that the primary cause of internal dampness is excess vapour from insufficient ventilation. There is also a mains water leak which may not have a direct impact on the dampness.

there was suck back on the glass of water when the stopcock was turn off, demonstrating a loss of water almost certainly caused by a leaking pipe under the floor.

. By taking a root cause approach, rather than a focus on blocking the symptoms of damp the savings are likely to be around £10,000. 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: Near low productive aquifer with intergranular flow See British Geological Survey.
Therefore risk of Rising Damp: low risk, see explanation by Dr Robyn Pender of Historic England.

I confirm that I inspected the property on 1 November 2024. I conclude that the primary cause of internal dampness is excess vapour from insufficient ventilation. there is also a mains water leak which may not have a direct impact on the dampness.. 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 1 November 2024

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.

Note neither condensation nor rising damp are causes. They are symptoms.

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.

FACT: dehumidifiers are a win-win as all energy is released as heat with a 50% bonus through enthalpy, but they need to be targeted to the source of the vapour or location of dampness and mould, should be insufficient, typically 20 L/ day theoretical capacity with 6 Litre container and decanted daily or drained into a sink or similar.

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.

Help It takes teamwork to solve damp and mould issues in properties. It isn’t easy or obvious. We can help with damp.ai. Time permitting the plan is to run online workshops for solving damp issues, within the community.

Mains water leak treated as if it were rising damp

Background

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Video evidence, tips & tricks

Data Evidence Explanations

Data loggers – see damp.ai/detect

Conclusion from data loggers

Evidence & Illustrations

Remedial actions

Recommended remedial actions

To keep the property dry

Optimal remedial actions

Actions if all else fails

Conclusions & reasoning

Conclusion summary for main concern

Reasoning

Root cause fix should save: £10,000

Risk of rising damp: low risk

Survey report & limitations

Site visit 1 November 2024

Damp & Survey methodology

W.H.O. indoor air quality guidelines

W.H.O. indoor air quality guidelines

FACTS about Condensation and Mould

TIPS To Stay Condensation and Mould Free

AI & related examples

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