Rising damp was diagnosed in a recent property purchase. A Homebuyers survey, conducted in August, followed by a Kenwood Damp Proofers Plc quote for work in early October, revealed high to moderate damp readings in three main areas: the front bay window, the party wall in the bathroom, and the wall behind the kitchen base unit. Both surveys indicated potential damage or bridging of the Damp Proof Course (DPC) at the front bay window. The Homebuyers survey suggested a salt barrier finishing plaster (a form of rising damp treatment), whereas Kenwood proposed a more expensive injection solution, quoting £4,000.
In early November, the new homeowner noticed that the walls by the front bay window were the central issue, with water accumulation along the skirting board, wet wall areas, and the emergence of black mould. Suspicions arose about the old bay windows with single glazing, rotting timber, and poor insulation, alongside concerns over the integrity of the external wall’s DPC. Despite high damp readings, no significant signs of damp were observed in the bathroom, which adjoins the neighbour’s property in this terraced housing. The homeowner also noted minor floor condensation issues near the back garden door, adding to the complexity of the damp problems identified in the property.
In conclusion, from the data loggers
- By implementing a quick fix to the bathroom ventilation and adhering to a few simple recommendations, you have saved yourself at least £4,000 and considerable disruption. The recommended damp proofing treatment for rising damp would not have solved the root cause, but rather it would have moved the problem along to the interface between the impermeable slurry and old plaster.
Evidence & Illustrations
Sub-floor vents are vital for safety, especially in case of undetected leaks, but they can also cause heat loss, increasing the risk of mould and condensation. To mitigate this, monitor the sub-floorrelative humidity regularly, perhaps weekly, using a hygrometer probe (readily available on Amazon or eBay for around £5). If conditions allow, you can block these vents with insulation or a cover, like the ‘Airbrick Flood Defence Cover’ found on eBay. To monitor, insert the hygrometer probe through a floorboard cracks or a hole drilled discreetly, such as under the central under stair cupboard. If humidity exceeds 85%RH for prolonged period, more than a day without decreasing, reopen the vent and investigate for leaks, for instance, by checking for pressure loss in the mains water. Be aware that failing to monitor can greatly increase the risk of timber rot. Also, consider that freeholder permission might be required for these modifications.
Insulation in the sub-floor vents
Note insulation reduces heat loss and therefore risk of mould and condensation, but needs to be accompanied by ventilation, dehumidification and strategies for maintain low dew points especially when away, such as leaving a dehumidifier to drip safely into a sink.
Using a dehumidifier to reduce the mould and condensationand reduce your carbon footprint
Utilising a dehumidifier not only combats mould and condensation but also optimises energy use, potentially reducing your carbon footprint. Dehumidifiers are uniquely efficient: all the energy they consume is released as heat, with an additional 50% heat bonus derived from the enthalpy process. This process occurs when water vapour condenses into liquid, releasing latent heat. In contrast, traditional electric heaters convert all their consumed energy directly into heat, without any such bonus. This inherent efficiency of dehumidifiers makes them a more environmentally friendly choice compared to standard electric heaters, as they provide added heat output for the same energy consumption.
- If used consistently, a dehumidifier will lower your carbon foot print, by about 50% compared to an electric heater and about 500 times less than a gas boiler (according to a ChatGPT calculation).
- Humid air feels colder than the equivalent dry air, so you can reduce the thermostat and therefore consumption of heat.
- You shouldn’t have to leave heating on when away, so long as the dehumidifier is running and safely dripping into a sink, except for making sure not to allow the temperature to drop below zero, which is anyway unlikely in a ground floor flat.
To keep the property dry
|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.
|Use fan to expedite drying
|Direct a fan onto the damp patch to speed up the drying process.
|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).
|Monitor vapour with data loggers
|Monitor relative humidity and temperature against the wall or ceiling to observe the effects of improvements, such as ORIA Wireless Thermometer Hygrometer (20m (2 Packs)) – already in place. In addition monitor improvements on the damp wall a pencil line and damp meter such as dr.wood moisture meter, logging improvements each month. Monitor relative humidity and temperature against the wall or ceiling to observe the effects of improvements, such as ORIA Wireless Thermometer Hygrometer (20m (2 Packs)) – already in place. In addition monitor improvements on the damp wall with a pencil line and damp meter such as dr.wood moisture meter, logging improvements each month.
|I would buy a Dr. Meter Wood Moisture Meter 2 in 1 Pin & Pinless Multifunctional Water Detector £23.99 to log and monitor reduction to dampness in walls.
|Stay above the mould and dew points
|Dew point is the temperature that condensation starts at. Either reduce vapour and or maintain heat especially late at night when it’s cold outside: More efficient alternatives include 1) insulating cold walls, 2) strategically placing one or more dehumidifiers, positioned where the night-time dew point is highest – use data loggers to locate the optimal position (typically a damp room near a damp wall, e.g., kitchen, bathroom). Personally, I run a dehumidifier whenever leaving a room unheated.
|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.
|Target vapour from cooking with an extractor fan
|Consider installing a kitchen extractor fan, ducted out.
|Remedial actions – estimate of costs
Actions if all else fails
|Monitor sub-floor humidity
|Sub-floor vents, while crucial for safety in case of unnoticed leaks, can lead to heat loss. By regularly monitoring the sub-floor relative humidity, such as weekly with a hygrometer probe (available on Amazon or eBay for around £5), you can safely block these vents with insulation and or a cover, (I use one off eBay “Airbrick Flood Defence Cover” £22). Insert the probe through floorboard cracks or a discreetly drilled hole. If the humidity rises above 85%RH for more than a day without coming back down, then open the vent and consider investigating for a leak, such as by testing for loss of pressure on the mains water. Neglecting to monitor, especially in the event of a leak, significantly increases the risk of timber rot. You may need freeholder permission.
|Consider targeted insulation
|Optimal actions – estimate of costs
I conclude that condensation and mould due to insufficient ventilation.
Inadequate ventilation, damp proofing treatment not a solution, the ventilation was improved during survey, solving the problem
fixed the vent issue in the bathroom. 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 Damp: highly unlikely, see explanation by Dr Robyn Pender of Historic England.
I confirm that I inspected the property on 231215SH0800. I conclude that condensation and mould due to 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.
Site visit 231215SH0800
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.
- Rising damp concern: You bought the property recently after being told by a surveyor and then a damp proofing contractor that you had rising damp.
- Damp treatment: Treated in the past with impermeable slurry
- Weather: Overcast
- Property: Victorian, ground floor flat in a terrace
- Background: Recently purchased, previous quote for rising damp treatment
- Changes: Conversion to flats, worsened by Covid and energy crisis
- Occupancy: Two people, sometimes working from home
- Mould & notes: Mould under sink, signs elsewhere
- Primary damp concern: Dampness in front bay, under sink, and bathroom
- Compounding: Heat loss in bay, sub-floor vents and cold zones in bathroom and kitchen
- Airbricks: Causing heat loss to front wall, linked to mould
- Sub-floor humidity: The sub-floor had normal levels of relative humidity.
- Tenure: Ground floor flat
- Attachment: Terraced
- Build: Victorian
- Walls: 9-inch thick solid walls
- Exterior comment: Dampness causing salt blisters on front wall, no penetrating damp
- Penetrating damp assessment: Not the primary cause
- Drains: No drain suspicions
- Leak signs: No signs of a leak
- Leak assessment: Leak unlikely to be a factor
- Floor: Suspended timber floor
- Loft: Not appropriate
- Timber assessment: No signs of timber issues
- Last dry: Damp noted in homebuyer survey
- Ventilation assessment: Fixed blocked vent, extended vent time
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.