Data loggers
- The calculated surface relative humidity is hitting 100%RH on the internal wall because the metal box is drawing heat out to the cold external air in the sub-floor void. The primary solution lies with moving the metal box or insulation it against cold from sub-floor air temperatures.
- In addition, I would not dry clothes internally without a dehumidifier or dry them in a vented room, such as the bathroom, with the door closed.
- Cook with tops on pots and pans, use the kitchen extractor fan if you have one, or keep a window open and door closed.
- Make sure the surface relative humidity in the coldest section of wall is not above 85%RH.
- Improve ventilation by running the bathroom extractor fan or keeping the window open for at least 30 minutes after a shower, with the bathroom door kept closed, at least until the bathroom is dry. This will force warm dry air from the property into the bathroom, speeding up the drying of the bathroom, without allowing vapour to diffuse, like smoke does, back into the property.
Evidence & Illustrations
Other matters
To keep the property dry | |
|---|---|
| Move the metal box | |
| Move the metal box away from the wall and or insulate it from external temperatures. | |
| Use fan to expedite drying | |
| Direct a fan onto the damp patch to speed up the drying process. | |
| 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%. | |
| 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. | |
| Check under rainwater drain | |
| Please ask the council to inspect and repair the drains located beneath the road. I don’t believe this is the root cause of damp in your property, but as a matter of good practice likely cracks should be inspected and repaired. | |
| Remedial actions – estimate of costs | £0 |
Actions if all else fails | |
|---|---|
| Consider using 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 |
| Consider instructing general builder to duct out kitchen extractor fan (hole required to duct outside). | |
| The main issue to getting ducting out the extractor fan. Ideally it should be using rigid ducting (not flexible as the ridges create eddies slowing air speed), as short as possible with as few bends. It can go up the chimney but would then need to be run for longer to account for the possibility of vapour travelling back down. | £200 |
| Consider replacing the bathroom extractor | |
| In my opinion, the optimal fans are ones that are targeted, with the fan located near the shower head (without being so close that water sprays onto it), removing vapour during and for at least 30 minutes after taking a shower or bath (which typically produces slightly less vapour). Ideally the fan should be separately wired up with an overrun. Installing the overrun can account for a majority of the cost. Consider installing a continuous flow extractor fan such as Brookvent Airstream DMEV 100 HT (Continuous Running Extractor Fan with Humidistat Timer). Note a continuous flow fan will expel warm air, thereby increasing heating cost by about £120 p.a. but this may be a small price to pay. You can use an isolator to manually turn off the fan when the property is sufficiently ventilated, but the risk is it is left off. | £300 |
| Optimal actions – estimate of costs | £680 |
I conclude that a large metal box is causing heat loss and therefore high surface relative humidity on an internal wall.
Heat loss causes condensation. The metal box draws heat out of the wall to the cold sub-floor air.
. 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 231026SH1200. I conclude that a large metal box is causing heat loss and therefore high surface relative humidity on an internal wall.. 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 231026SH1200
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: You were concern you might have rising damp.
- Damp treatment: The wall appears to have been damp-proofed, hiding the problem rather than dealing with the root cause.
- Weather: Some sun, 16°C, 75% relative humidity.
- Property: Probably Edwardian.
- Background: Purchased property during Covid, had been some issues. Flagged by surveyor, but nothing major.
- Changes: Painted exterior, hardcore driveway, open plan and always certainly damp before treatment.
- Occupancy: Young family.
- Mould & notes: I saw the neighbour’s side of the same property. There was dampness, but not to the same extent.
- Primary damp concern: Damp along the party wall, mainly on the central side of the front reception.
- Other damp concerns: None.
- Compounding: Heat loss caused by the metal box above a cold floor. Other compounding factor, although there is a sign of a depressed section in the drive, which could result in ponding.
- Airbricks: There are air bricks that appear to be sufficient.
- Sub-floor humidity: Humidity was average.
- Tenure: house
- Attachment: a semi-detached
- Build: Edwardian
- Walls: 9 inch.
- Exterior comment: Exterior appeared to be in good order.
- Penetrating damp assessment: The could be rainwater in the soil compounding damp issues, but I doubt it
- Drains: There are no obvious signs of drain defects.
- Leak signs: There is a sign of a mains water leak.
- Leak assessment: I doubt there is leak
- Floor: Suspended timber floor.
- Loft: The loft has been converted, but I didn’t check it specifically.
- Timber assessment: Check that moisture evaporates away from the wall once the box is removed, ventilation or dehumidification improved. There is always a risk of rot in the sub-floor void, but if the sub-floor relative humidity remains below 85%RH, the risk is low.
- Last dry: I understand some damp issues were identified at the time of the purchase during Covid.
- Ventilation assessment: The bathroom and kitchen ventilation is inadequate
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.
