The hallway of the property is experiencing recurring damp issues. Despite implementing damp-proofing measures two years ago, the problem persists in certain areas. To address these concerns, recommendations from a previous damp survey were followed, yet they did not resolve the issue. These included: filling all vent holes with thermal plasterboard, followed by skimming and painting; installing a wall-mounted electric heater with a timer on the garden-facing wall in the rear bedroom; washing down and repainting the walls around the rear and bay windows in the reception room with anti-fungal paint; and replacing the blinds on the rear bedroom window with curtains set outside the window box. Despite these interventions, damp and mould continue to be a challenge in the hallway.
In conclusion, from the data loggers
- Dew points are important to understand. The warmer the air, the more vapour it can hold. Conversely the colder air is, the less it can hold, until you get to the dew point when air is saturated with moisture, cannot hold anymore and so condensation takes place below this temperature. The dew point is the temperature in °C, when air is saturated, i.e. 100%RH. The more vapour in the air, the higher the dew point temperature is, and therefore the greater the risk of condensation. Dew point and vapour quantity or vapour pressure, exactly match each other. Ventilation blows out vapour laden “stale air”, replacing it with external air, with the vapour quantity and therefore dew point of the outside. A well ventilated property should have a dew point similar to the outside. The only way to drop below the external dew point is through condensation such as with a dehumidifier, which you should use if ever drying clothes internally.
- The dew point should be lowered by use of ventilation and dehumidification, to line up with, or ideally below the external temperature, as can be seen in the example property (my own). There is a risk of condensation on cold surfaces unless the dew points are lowered by properly ventilating, such that human generated vapour is removed, of by use of a dehumidifier.
- The dotted green line is the surface relative humidity (humidity of the cold surface) taking into account the dew point of logger 1 and the surface temperature. As can be seen the wall regularly reaches 100%RH when condensation takes place, and is persistently above 85%RH when mould growth is at risk.
- There are daily spikes in dew point (vapour production), sometimes midday, 6pm and midnight, but it does vary. I’m guessing this is bathroom or shower times.
- The tenant should be shown these graphs and the dew point on the data logger. We also publish daily forecast temperature, and mould and dew points for London in winter; on https://twitter.com/mouldpoint
- I am not convinced any of the previous recommendations would have addressed the excessive level of vapour, i.e. lower the dew point, in the internal atmosphere. Insulation will benefit the wall being insulated, but not the remainder of the property, likewise heat will benefit the wall being heated.
Evidence & Illustrations
To keep the property dry
|Ask tenants to remove vapour from bathroom
|Ask tenants to keep the bathroom door closed with the fan running until the humidity from the shower has subsided – typically at least 30 mins after the last shower. Consider adding a spring to the bathroom door as an extra reminder.
|Ask tenants to remove vapour from clothes drying
|I would provide tenants with a means of drying clothes internally, which could be a powerful dehumidifier or tumble dryer (like a heat pump). Alternatively ask them to dry in an vented room with the door closed (possibly a bathroom with the extractor running or window open). Ask tenants to never to dry clothes in an unventilated room. Consider offering to pay for the cost of running a dehumidifier or heat pump dryer, in the region of £1 per day, plus it is energy efficient as all energy is converted to heat plus a 50% bonus.
|Ask tenants to remove vapour from cooking
|Cook with tops on pots and pans to reduce the production of vapour from cooking by 80% and always run the kitchen extractor fan when cooking..
|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). The tenants should be able to reduce her energy consumption as dryer air feels warmer than humid air, therefore she can both reduce the risk of condensation and mould and her heating bill using a dehumidifier.
|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.
|Keep objects away from walls
|Move the mirror away from the window in the corridor and toys and other items away from walls to allow for air circulation.
|Use fan to expedite drying
|Direct a fan onto the damp patch to speed up the drying process.
|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. Aim to keep the dew point on the data logger below the external temperature at least until you are confident of success. In addition monitor improvements on the damp wall a pencil line and damp meter such as dr.wood moisture meter, logging improvements each month.
|Remedial actions – estimate of costs
Actions if all else fails
|Consider targeted insulation
|Consider targeted insulation: insulating behind radiators to stop heat loss, insulate coving, such as with polystyrene coving and filling the sub-floor air brick opposite the bathroom with expandable foam, covered in render and silicone around the outside of the front cable.
|Tenancy agreement for damp
|Consider updating the tenancy agreement, see Tenants responsibility to stay mould and damp free, or at least communicate to tenants their responsibilities, and praise them for already communicating. Dealing with damp and mould requires teamwork, communication and appreciation that it is not always easy for tenants, nor do they necessarily understand their challenges and responsibilities.
|Optimal actions – estimate of costs
I conclude that there was condensation and mould caused by mould. The key issue appears to be the heated dyer and possibly not keeping he bathroom door closed and vent running fast.
The flat is warm and there is good ventilation in the bathroom and kitchen, however it is cluttered, clothes are dried internally and the bathroom door may be left open.
I opened trickle vents. By taking a root cause approach, rather than a focus on blocking the symptoms of damp the savings are likely to be around £2,000. This contrasts with typical damp proofing contractor recommendations such as chemical treatment for rising damp and untargeted ventilation, such as PIV systems.
Flood risk: Low 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: highly unlikely, see explanation by Dr Robyn Pender of Historic England.
I confirm that I inspected the property on 231122SH1000. I conclude that there was condensation and mould caused by mould. the key issue appears to be the heated dyer and possibly not keeping he bathroom door closed and vent running fast.. 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 231122SH1000
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 were concern you might have rising damp.
- Damp treatment: Despite the low risk of rising damp, there has been an attempt at chemical treatment against rising damp. Rising damp treatment is normally a sign of insufficient ventilation. The walls have been drilled into by about 200mm and injected with damp proofing chemicals. In theory the chemicals are absorbed into the brick pores reducing the bricks ability to absorb moisture. Walls are replaced with damp proofers slurry. This can cause problems with absorption imbalance, resulting in increased condensation on other walls or vapour becoming absorbed and trapped behind the slurry. There was evidence of surface condensation in areas probably not treated with replacement plaster but no evidence of trapped vapour. The solution is through ventilation and humidity control.
- Weather: dry overcast
- Property: Victorian ground floor flat
- Background: The property was surveyed and treated a few years ago, with limited success. There has been a new tenants since then.
- Changes: conversion into flats, central heating, double glazing with no or insufficient trickle vents and lifestyle changes including more frequent showers and clothes washing, extension to rea, including greater occupancy during the Covid pandemic.
- Occupancy: Young family
- Mould & notes: Mould on cold walls
- Primary damp concern: Dampness and mould along corridor next to bathroom.
- Compounding: Clothes dryer
- Airbricks: There is a solid floor no need for air bricks.
- Sub-floor humidity: Much of the rear, under the damp is above a solid floor.
- Tenure: ground floor flat
- Attachment: a terraced
- Build: Victorian
- Walls: solid wall made of two brick widths (225mm)
- Exterior comment: There were no major concerns seen externally that would account for internal issues.
- Penetrating damp assessment: The exterior appeared to be OK from a damp perspective. There are no obvious signs of significant penetrating damp.
- Drains: The drains are of no special concern.
- Leak signs: No suspicion of a mains water leak
- Leak assessment: There are no obvious signs of a significant mains or wastewater leak.
- Floor: The ground floor felt solid.
- Loft: There was no loft.
- Timber assessment: There are no suspicions of significant timber decay.
- Last dry: I understand damp issues have crept up over time with the new tenants.
- Ventilation assessment: The bathroom extractor fan is fast but noisy. There is an externally ducted kitchen extractor fan. Clothes are dried internally.
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.