Damp patches have been observed appearing on the flank wall following periods of rainfall, leading to investigations and replacements of the roof, windows, and external render by multiple builders. Despite these efforts, the issue persists, prompting a request for expert judgment to be provided before any further expenditures are undertaken. The situation underscores the complexity of diagnosing and remedying damp problems, highlighting the necessity for specialised expertise to identify the underlying cause and recommend effective solutions.
In conclusion, from the data loggers
- There are large variances in the dew points, suggest insufficient bathroom and background ventilation, that is mainly from the kitchen and drying clothes, but also from respiration.
- The dew points are well above the external temperature. A well ventilated or dehumidified property should more or less match external temperatures.
Evidence & Illustrations
There was also mould in the bedroom, used as a home office. Mould growth occurs where relative humidity exceeds 85%RH for more than six hours. Excessive humidity is usually due to insufficient ventilation, poor air circulation, and cold surfaces. Relative humidity measures the amount of vapour in the air relative to the air’s capacity to hold vapour. It is influenced by vapour pressureand 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.
To keep the property dry
|Use a dehumidifier
|To manage relative humidity, especially when poorly ventilated, humid or cold, consider using 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 – optimal for colder environments) – all highly rated by Which!. There are numerous alternatives if these specific models are not available. When selecting a dehumidifier, prioritise factors like daily and tank capacity, low noise levels, the availability of a continuous drainage option, and ease of use for programming functions, over aesthetics and weight. The technology behind dehumidifiers is well-established and straightforward to produce, ensuring you can find a suitable alternative focusing on a minimum daily capacity of 20L and the presence of a continuous drainage feature.
|Use fan to expedite drying
|Direct a fan towards any damp areas to expedite the drying process.
|Target vapour from bathroom
|After showering, keep the bathroom door closed and the window open or fan running for at least 30 minutes to allow vapour to dissipate.
|Target vapour from cooking
|Always use tops on pots and pans to reduce vapour emission by 80% and where applicable use an externally ducted kitchen extractor fan.
|Target vapour from clothes drying
|Opt for a tumble dryer, dry laundry in a well-ventilated room with the door closed (such as a bathroom with the extractor fan on or window open), or employ a sufficinetly high capacity dehumidifier. Avoid drying clothes in poorly ventilated areas and anywhere near cold walls.
|Mark improvements on damp walls with a pencil line or sticky note and use a moisture meter, such as the Dr. Meter Wood Moisture Meter 2 in 1 Pin & Pinless Multifunctional Water Detector £23.99 or similar damp meter, to log and monitor reduction to dampness in walls. By doing so, you will gain early confidence in these recommendations. Use devices like the ORIA Wireless Thermometer Hygrometer to monitor relative humidity and temperature near walls or ceilings, look to keep the dew point at or below the external temperature. The dew point is shown on the app (if not use https://mouldpoint.co.uk to calculate the dew point from humidity and temperature readings).
|Stay above the mould and dew points
|The dew point indicates when condensation begins, showing the air’s moisture content. To avoid condensation and mould, ensure proper ventilation and dehumidification keep the indoor dew point below the outdoor temperature. Use targeted extractor fans and strategically place dehumidifiers in areas prone to vapour production or dampness. Operating a dehumidifier in bedrooms before bedtime, by clothes drying during the day, and in kitchens overnight is highly effective. Always run at least one dehumidifier when leaving a property vacant, especially in winter. Place it on a sink to catch leaks, with the door open and the window closed, set to 70%RH. Doing this allows you to turn the heating down to its minimum to protect against frost, saving money while minimizing the risk of mould and condensation.
|Keep objects away from walls
|Reposition furniture and open curtains away from walls, to improve flow of air from the radiator to damp walls.
|Remedial actions – estimate of costs
Actions if all else fails
|Bathroom extractor fan
|For optimal vapour removal from the bathroom consider installing a continuous flow bathroom extractor fan, such as the Vent-Axia Extractor Fan With Humidistat & Timer or the Brookvent Airstream DMEV 100 HT. These should ideally be installed away from the door, nearer to the shower, with rigid ducting to minimize air resistance and potentially insulated for long runs.
|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.
|Consider targeted insulation
|After ensuring walls are dry and mould-free, consider insulating damp walls with thermal lining paper, such supplied by Rockwool.
|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.
|Optimal actions – estimate of costs
I conclude that dampness primarily caused by condensation from excess vapour due to insufficient ventilation, made worse by heat loss.
the bathroom extractor fan isn’t working. There is mould elsewhere in the property, which there wouldn’t be, unless there was excess humidity. The damp zone is just in the shade in winter, and next to the bathroom which is not used and therefore probably colder than it would otherwise be
I tried to repair the bath extractor, without success. By taking a root cause approach, rather than a focus on blocking the symptoms of damp the savings are likely to be around £5,000. This contrasts with typical damp proofing contractor recommendations such as chemical treatment for rising damp and untargeted ventilation, such as PIV systems.
Flood risk: No risk See Flood Risk (note most flood risk is not from groundwater).
Sub-soil rocks: Rocks with essentially no groundwater See British Geological Survey.
Therefore risk of Rising Damp: remote possibility, see explanation by Dr Robyn Pender of Historic England.
I confirm that I inspected the property on 240109SH1200. I conclude that dampness primarily caused by condensation from excess vapour due to insufficient ventilation, made worse by heat loss. 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.
Site visit 240109SH1200
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.
For survey purposes, damp is defined as unwanted water. Water brings life. We need it. Unfortunately, fungus and insects also thrive in water. While a damp wall can cause decorative spoiling, it is not moisture, but the life it brings that causes the greatest concern in the home environment. FACT: vapour causes 85% of residential damp problems.
Independence and Methodology
Our only income is through damp survey fees. We are independent of contractors and never profit from remedial work. We do not receive or pay any fees or other inducements. Our motivation is peace of mind and practical, durable solutions. We use an array of equipment to identify the root cause of damp within walls. Our damp surveys follow guidance from RICS, Historic England and PCA joint position statement and support RICS’s highest standard, level 3 “Home Survey Standard” (HSS).
During the survey we assess likelihood of rising damp*, mainswater leak, penetrating damp, condensation, timber rot and woodworm. We profile the damp patches and consider the likely sources of dampness and test ventilation against building regulations requirements. We consider changes to the property and factors just before the first sighting of damp.
- Weather: inclement
- Property: 1920s end of terrace or semidetached
- Background: a lot of money has been spent on remedial work including replacing the external render without benefit
- Changes: loft extension
- Occupancy: family
- Mould & notes: mainly dampness, including calcium sulphate on surface, but some signs of mould
- Primary damp concern: a circle of damp in line with the extension to the loft on the flank wall
- Other damp concerns: dampness on the ground floor, utility and toilet wall
- Tenure: House
- Attachment: semidetached
- Build: 1920s
- Walls: 9 inch, thick wall
- Exterior comment: there are some small cracks in the external render, but no signs of penetrating damp internally
- Penetrating damp assessment: penetrating damp does not appear to be the primary course
- Leak signs: no signs of leak
- Leak assessment: The bathroom which would be the only source of damp in the area isn’t being used and therefore does not appear to be the root cause nor is the colour one characteristic of leak
- Floor: not a concern
- Loft: loft conversion
- Timber assessment: there appears to be no risk to timber
- Last dry: There has been an ongoing problem since the property was purchased
- Ventilation assessment: there is insufficient ventilation from the bathrooms and kitchen
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.