Background
Black mould, in the corner of bedrooms and bay, is perplexing.
Data loggers
In conclusion, from the data loggers
- There need to be a massive focus on reducing internal vapour (dew point) through targeted ventilation and dehumidification, including vapour released from drying clothes. See https://dampsurveys.com/cases/why-dehumidifers-are-the-best-weapon-against-mould/
- I would increase use of ventilation, consider replacing defective facts and ducting and increase the amount of water removed using a higher capacity dehumidifier, increasing the airflow around the corner, see recommendations.
Evidence & Illustrations
Targeted ventilation
Fast, targeted ventilation plays an essential role in managing vapour (dew points) within properties, ensuring they remain at or close to external dew points, which is crucial for preventing mould growth. The German method of ventilating homes by opening windows in the morning can be effective but often results in significant heat loss. Moreover, much of the vapour in a home is produced later in the day, particularly during activities like cooking. In the UK, with its wetter climate, external air tends to have higher dew points, making the management of internal humidity even more important.
According to UK building regulations, bathrooms should have a ventilation rate of at least 15 litres per second, with a 30-minute overrun and closed doors to ensure effective moisture removal. Kitchens, especially when cooking, require a higher ventilation rate of 30 litres per second to remove excess moisture and odours, not just during the cooking of smoky or spicy foods. Noisy extractor fans might discourage their use, suggesting the potential need for replacement with quieter models.
Areas in homes, like cold external corners and bays, are at an increased risk of heat loss due to their larger external surface areas. This loss can elevate surface relative humidity to over 85%RH, the threshold at which mould growth becomes a risk. In such scenarios, the role of dehumidification becomes critical, particularly in poorly insulated properties.
Dehumidification helps in maintaining lower internal dew points, a crucial factor during rainy conditions when external air is saturated with moisture. The replacement of vented air with air at the external dew point through dehumidification can significantly reduce the likelihood of condensation and mould growth. When internal wall temperatures are close to external temperatures, dehumidifiers can effectively lower the internal dew point, preventing the conditions that allow mould to thrive.
In summary, good targeted ventilation, along with the strategic use of dehumidifiers, is vital in maintaining appropriate dew points, especially in the UK’s humid climate. Such measures are crucial for preventing mould growth and ensuring a healthy living environment.
To keep the property dry | |
|---|---|
| Instruct the builder to complete ventilation | |
| Instruct the builder who installed the ventilation in the ensuite bathroom to complete there ducting out of the building and make sure the fan is operating correctly. You may have to have an specialist fan installer to finish off the work of the pervious builder. | £20 |
| Remove mould | |
| 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. | £20 |
| Maintain airflow close to cold walls | |
| TIP: To prevent condensation and mould build-up, it’s crucial to keep objects away from cold walls. Insulating cold internal surfaces can be a highly effective solution, consider using Wallrock Thermal Liner in bedroom bay. Also consider moving cupboards away from the corner. | |
| Reduce allergenic dust mites | |
| TIP: To reduce damp-related allergies from dust mites, regularly turn bedclothes and pillows, rotate the mattress, vacuum carpets near cold walls, and wash bedclothes weekly, especially during high humidity and low temperatures. | |
| Use fan to expedite drying | |
| Direct a fan onto the damp patch to speed up the drying process. | |
| Keep some late night heat | |
| TIP: Maintain a small amount of heat 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. | |
| Reduce vapour from cooking | |
| Cook with tops on pots and pans to reduce the production of vapour from cooking by 80%. | |
| 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). | £180 |
| Remedial actions – estimate of costs | £220 |
Actions if all else fails | |
|---|---|
| Consider replacing the noisy kitchen extractor | |
| A noisy fan is unlikely to be used often when cooking, yet the kitchen is open plan, with a warm water fish tank, so needs extra help removing vapour. | £200 |
| 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. | |
| Consider targeted insulation | |
| Internal insulation into cupboard, especially in the cold corners. Consider moving the cupboards away from the cold corner to increase flow or warm air currents. | £1,000 |
| Optimal actions – estimate of costs | £1,200 |
I conclude that condensation and mould from excess vapour.
Inadequate bathroom extractor fans, one terminating in loft
I improve the vent in the family 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: 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 231213SH1400. I conclude that condensation and mould from excess vapour. 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 231213SH1400
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.
- Rising damp concern: None
- Damp treatment: Likely treated against rising damp
- Weather: Overcast, cold
- Property: 1920s
- Background: Long-term mould and condensation issues
- Changes: Modernised with showers and bathrooms, including ventilation
- Occupancy: Family
- Mould & notes: Mould in external corners and in the bay
- Primary damp concern: Condensation and mould
- Compounding: Poor ventilation causing vapour to meet cold surfaces
- Airbricks: There appears to be a solid floor.
- Sub-floor humidity: Not relevant as there appears to be a solid floor.
- Tenure: house
- Attachment: Detached
- Build: 1920s
- Walls: Solid, probably
- Exterior comment: No major external concerns
- Penetrating damp assessment: No significant penetrating damp
- Drains: No drain concerns
- Leak signs: No signs of leaks
- Leak assessment: Low leak risk
- Floor: Appears to be solid
- Loft: Reasonably insulated, however there are ventilation issues
- Timber assessment: No timber issues
- Last dry: Increased occupancy and energy costs during Covid
- Ventilation assessment: Bathroom vents are insufficient
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.
