Background
Mould growing all around a recently purchased rental flat in a 1960s block. Condensation is forming at the base of walls. While it looks like rising damp, it would be more accurately described as falling damp, piling up (but ‘rising damp’ is better ‘click bait’ and a more visual or alarming metaphor).
Data loggers – to follow
In conclusion, from the data loggers
- To follow
Evidence & Illustrations
Freeholder responsibility for mould
We often have leaseholders of properties trying to persuade us that mould is a freeholder responsibility. Mould, is never the responsibility of freeholders, with almost no exceptions, except may be where a vent duct was blocked by freeholders. If there is general mould, then there is insufficient ventilation. In this case neither the bathroom, nor kitchen vents were extracting vapourfrom the property.
Working out if you are ventilation sufficiently
The only way to know if you have insufficient ventilation is to compare the concentration of vapourin internal air to external air. In a well ventilated property, the internal vapour should exactly match external vapour. Dew points are a way of determining concentration of vapour in air. The external dew point can never exceed the external temperature, otherwise it would rain (a form of condensation). Internal vapour will never condense on internal walls if the internal dew point is kept below the external wall temperatures through good ventilation and dehumidification. The risk of mould is also exceptionally low if internal vapour, as measured by dew point, is kept below the external air temperature, which you can find for the local area from BBC or meteo websites.
Cold bridging
There is a lot of talk about cold bridging causing damp and mould. Yes cold bridging increases the risk of damp and mould, but it is never the root cause. The root cause is excess vapour, see above notes about keeping the internal dew points as measure in °C below the external temperature.
To keep the property dry | |
|---|---|
| Install a bathroom extractor fan | |
| Consider installing a continuous flow bathroom extractor fan such as Vent-Axia Silent 7.5W Extractor Fan With Humidistat & Timer Continuous or Brookvent Airstream DMEV 100 HT (Continuous Running Extractor Fans with Humidistat and Timer) – I have installed one in a rental property I own myself, that was bought cheaply because of mould. Although important to have an isolator, it can be sited in a way that doesn’t tempt tenants to use it. Ideally the vent should be located away from the door, closer to the shower. I would also install a bathroom spring to encourage tenants to keep the door closed. Ideally the ducting should be rigid, for reduced air resistance, and insulated to reduce risk of condensation in pipe. | £600 |
| Duct out kitchen extractor fan | |
| Instruct a general builder to duct out kitchen extractor fan (hole may be required to duct outside, possibly through glass, which may require freeholder permission). I would wire the vent separately from the sockets and insist that tenant use the extractor whenever cooking. | £300 |
| 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. | |
| 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 |
| 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. | £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. | |
| Reduce vapour from cooking | |
| Cook with tops on pots and pans to reduce the production of vapour from cooking by 80%. | |
| 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. | |
| Monitor improvements | |
| 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. | £24 |
| Keep objects away from walls | |
| Consider moving furniture away from mouldy walls and vacuum carpets regularly to reduce the build up of dust mites. | |
| Remedial actions – estimate of costs | £1,304 |
Actions if all else fails | |
|---|---|
| Consider updating your tenancy agreement | |
| I would replace the current bathroom fan with a continuous flow bathroom extractor fan that is quiet, fast fan, set-up with a 30-minute overrun, connected to a rigid duct (not a flexible duct), with external flaps (check the exit speed is about 15 l/s, see simple to use anemometer below). I would put a spring on the door to ensure that it is kept closed. I would also install a kitchen extractor fan ducted out and provide a 20L per day capacity dehumidifier. In addition I would make monitoring humidity and keeping good ventilation or dehumidification, such that the internal dew point is never above the external temperature for long periods (i.e. more than a day) at a time, as part of the AST (tenancy) agreement, explaining ow the ventilation works, the importance to the property and the tenant of using the ventilation correctly and monitory internal vapour making sure that the internal dew point doesn’t exceed the external temperature. | |
| Consider targeted insulation | |
| I don’t think the cost justifies the benefit, but you could consider Wallrock thermal lining paper. Insulation is never the primary solution, but can mitigate the risk. The root cause is the poor ventilation, the solution is improved provision of ventilation, use of ventilation, dehumidification and monitoring. | £500 |
| Optimal actions – estimate of costs | £500 |
I conclude that there was condensation and mould caused by insufficient ventilation made worse by thermal imbalance.
These properties were built at a time when people showered and washed clothes weekly using windows to provide sufficient ventilation. Modern living needs mechanical ventilation
. 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: No risk See Flood Risk (note most flood risk is not from groundwater).
Sub-soil rocks: Near moderately 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 240220SH1430. I conclude that there was condensation and mould caused by insufficient ventilation made worse by thermal imbalance. 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 240220SH1430
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: Your tenant was concerned about condensation and mould growth.
- Damp treatment: Despite the low risk of rising damp, the neighbour has attempted chemical treatment against rising damp. Rising damp treatment is normally a sign of insufficient ventilation.
- Weather: dry overcast
- Property: 1960’s
- Background: The property was purchased as a rental property last summer when it was dry, dampness and mould has shown since then.
- Changes: lifestyle changes including more frequent showers and clothes washing, including greater occupancy during the Covid pandemic.
- Occupancy: tenant
- Mould Colour: mould across flat, especially in cold areas will reduced air circulation
- Primary damp concern: dampness and mould across property
- Compounding: heat loss from lintels
- Airbricks: There is a solid floor no need for air bricks.
- Sub-floor humidity: There appears to be no sub-floor void.
- Tenure: ground floor flat
- Attachment: a terraced
- Build: 1960’s
- Walls: probably cavity walls, without insulation, but this is not a defect,
- 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 floor is of no special concern.
- Loft: There was no loft.
- Timber assessment: There are no suspicions of significant timber decay.
- Last dry: I understand there were no damp issues when you bought the property.
- Ventilation assessment: There is no mechanical bathroom extractor fan nor ducting out of the property from the kitchen extractor fan.
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.
