Background
The flat has been owned for nearly eight years, with damp issues often treated cosmetically rather than fundamentally. Major concerns include poor drainage and improperly draining gutters impacting the main external wall, as depicted in attached images. Ventilation issues are also apparent, with significant condensation on older, unreplaced windows during colder months, and orange deposits visible in the cellar, indicative of past inadequate treatments. Efforts are being made to resolve these root causes to prevent future problems and enhance the living experience.
Data loggers
The grey line at the base of the graph, is the dew point differential. Dew point is both a measure of vapour in air expressed as °C and the temperature that condensation takes place at. When the line is below zero, as in this case, there in more vapour in the bathroom compared to the hall. This points to the bathroom as being a major source of vapour.
In conclusion, from the data loggers
It is summertime, but if you keep this level of vapour management then you have little risk of damp next winter, i.e. keep internal dew points below the external temperature. I encourage you to follow recommendations including; use a 20L/day dehumidifier, don’t use the heated rail and bleach or otherwise remove mould (see recommendations).
Evidence & Illustrations
To keep the property dry | |
|---|---|
| Target vapour from bathroom | |
| Keep the bathroom door closed with the fan running or window open until the humidity from the shower has subsided—typically at least 30 minutes after the last shower. Keeping vapour in the bathroom dramatically reduces the risk of mould elsewhere in the property but may increase the risk of mould in the bathroom, necessitating regular mould wipe-downs. Consider using a little HG Mould Remover Foam Spray on vulnerable areas such as cold zones and seals in the bathroom weekly. | |
| 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 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 outlet, 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 outlet (use this to drip into a sink when away in winter). A dehumidifier will save money compared to heating a property. Like an air source heat pump, for every £1 of energy spent on a dehumidifier, you get back roughly £1.50 of heat. Furthermore, when it’s cold, dry air feels warmer than humid air, so a dehumidifier will reduce energy consumption both when at home and away (as you don’t need to heat the house to stop mould). | £180 |
| Target vapour from clothes drying | |
| If needing to dry clothes inside, use a powerful dehumidifier (20 litres per day or more – see above) near the clothes dryer. Don’t dry clothes in an unventilated room and avoid heated clothes racks, as they can produce vapour at a faster rate than dehumidifiers can remove it. | |
| Keep objects away from walls | |
| Consider moving furniture and objects away from cold walls affected by damp to improve airflow, thereby reducing the build-up of relative humidity. Most damp-induced allergies result from dust mites, which colonise in the same conditions as mould grows, which is why mould is often the only tell-tale sign. To reduce mites, vacuum around cold zones daily, turn duvets and pillows daily, wash sheets weekly, making sure they are fully dry (outside or using a dehumidifier) and turn the mattress weekly. | |
| Reduce vapour from cooking | |
| Cook with lids on pots and pans to reduce the production of vapour from cooking by 80%. Use a ducted extractor fan if available and whenever cooking. | |
| Monitor vapour with data loggers | |
| Monitor relative humidity and temperature against the damp wall or ceiling to observe the effects of improvements, such as the ORIA Wireless Thermometer Hygrometer (20m (2 Packs)). Keep dew points (as seen at the base of each meter on the SensorBlue app) at or below the external temperature (which you can find on https://www.metoffice.gov.uk or https://www.bbc.co.uk/weather. Additionally, monitor improvements on the damp wall with a pencil line and damp meter such as the Dr. Wood moisture meter, logging improvements each month. | |
| Remove mould | |
| Sand down mould where dry, and remove it with either bleach or anti-mould foam. I personally use HG Mould Remover Foam Spray, but I imagine there is no major difference between brands. | £100 |
| Remedial actions – estimate of costs | £280 |
Actions if all else fails | |
|---|---|
| Install a kitchen extractor fan | |
| I would instruct a general builder to install and duct out a kitchen extractor fan. The most important element, often overlooked because it can be challenging and time-consuming, is ducting to the outside. Ideally, it should use rigid ducting (not flexible, as the ridges create eddies that slow airflow) and be as short as possible with as few bends. Also note that ideally, a kitchen door should be present, thereby reducing the diffusion of vapour into other parts of the property. Cook with lids on pots and pans, and use a dehumidifier to further control moisture. | £500 |
| Improve bathroom ventilation | |
| Consider replacing the bathroom extractor fan (with a flow of 15L/S or more after installation) with at least a 30-minute overrun. Given the issues, I would install continuous flow bathroom extractor fans such as Brookvent Airstream DMEV 100 HT (Continuous Running Extractor Fan with Humidistat Timer). Once the fans are ducted out properly, make sure to keep the bathroom doors closed and fan running until dry, normally at least 30 minutes after taking a shower. | £600 |
| Consider targeted insulation | |
| I don’t think the cost justifies the benefit, but you could consider Wallrock thermal lining paper around the zone showing signs of damp. Insulation is never the primary solution but can mitigate the risk. The root cause is poor ventilation; the solution is improved provision of ventilation, use of ventilation, dehumidification, and monitoring. | £1,000 |
| Monitor sub-floor humidity | |
| Use a hygrometer, like the data loggers, to monitor sub-floor relative humidity. The sub-floor relative humidity will fluctuate. If it remains above 85%RH for an extended period then consider installing a fan into the sub-floor to blow air out. Increasing ventilation is tricky as there is limited accessibility. A company called ELTA made a Sub-Floor Ventilation Fan, which many clients with similar issues have installed with success, but ELTA have been closed down. This site seems to offer the same unit: https://www.builders-superstore.co.uk/product/ventilation-fan-sub-floor-mains-powered/ | £1,000 |
| Cellar options | |
| 1) Do nothing, 2) Remove impermeable or semi-impermeable paint from cellar walls and replace with permeable paints like lime-based options to allow walls to breathe and moisture to evaporate naturally. 3) Structural water proofing; evaluate the feasibility and cost-effectiveness of structural waterproofing methods, such as plastic membranes, although these should be carefully considered due to their potential to trap moisture and push it elsewhere. | |
| Maintain Rainwater Goods | |
| Every 6 months, during or soon after a rainstorm, check the flow of water to ensure that rainwater goods—gutters, downpipes, and drains—are clear of blockages and functioning properly. | |
| Install Rain-Guard | |
| Consider fitting a rain-guard (weather bar or weatherboard) under external doors to prevent rainwater from entering under the door. | £100 |
| Optimal actions – estimate of costs | £3,200 |
I conclude that the primary cause of internal dampness is excess vapour from insufficient ventilation.
Mould is only ever caused by excess vapour. In the case of mould in numerous zones across a property, such as seen here, is a sign of poor ventilation or insufficient dehumidification as a whole.
I fixed the defective bathroom extractor fan switch. 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: Near low productive aquifer with intergranular flow See British Geological Survey.
Therefore risk of Rising Damp: highly unlikely, see explanation by Dr Robyn Pender of Historic England.
I confirm that I inspected the property on 240524SH0800. I conclude that the primary cause of internal dampness is excess vapour from insufficient ventilation. 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 240524SH0800
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?