Background
This flat is a two-bed and is generally fine, but the bathroom has significant amounts of water on the ceiling and walls. The ceiling sits in under steps which lead to the main part of the property. There is also a slope leading towards the front door and a drainpipe which may be causing issues.
Efforts have been made, including keeping the window open and the installation of an extractor fan; however, the persistence of the problem has been noted. Additionally, concerns have been raised about the likelihood of this moisture issue leading to mould formation in other areas of the property.
Data loggers
The graphs are screenshots taken from your hygrometers, which I was able to access remotely.
In conclusion, from the data loggers
- The left-hand blue line in the graph is an approximation to the surface relative humidity, based on the temperature of the cold wall relative to the data logger. It illustrates the surface relative humidity over time. Surface RH is clearly peaking at around 100%RH when condensation takes place, and is often above 85%RH for prolonged periods, when mould grows.
- NB: I have less to say about the data, as I was unable to download a .csv file (with minute by minute temperature and humidity data). I have less experience with the brand of data loggers chosen, compared to ORIA Wireless Thermometer Hygrometer. Oria are BlueTooth, therefore cannot be used remotely. I believe these are SwitchBot. They are good for remote monitoring, but for a reason that is beyond me, it doesn’t seem possible to download the data, which clearly is held on the logger.
- I spent time explaining the issues with the tenant, who seemed receptive. The key solution is to close the bathroom door, keeping the light on.
Evidence & Illustrations
While there are short-term solutions. If this were my property, I would install a continuous flow extractor fan. Such a fan stays on at about 5l/s constantly with a humidity or lights switch operated boost to 15 l/s.
The under stair rooms, primarily designed for coal storage, in all these Victorian properties, is at risk of penetrating damp from the stair above. However, I saw not clear signs of ingress and it is not the primary cause of dampness here, which is excess vapour.
To keep the property dry | |
|---|---|
| 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. | £100 |
| Ask tenants to remove vapour from bathroom | |
| Ask tenants to 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. 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 (I’ll detail in second section) 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 | |
| Use the extractor fan whenever cooking. Cook with tops on pots and pans to reduce the production of vapour from cooking by 80%. | |
| Monitor vapour with data loggers | |
| Monitor relative humidity and temperature against the wall or ceiling to observe the effects of improvements, such as WIFI Wireless Thermometer Hygrometer (20m (2 Packs)) – already in place. Look for spikes above 70%RH, especially when away, without heating, when a dehumidifier should be left on. | |
| Use a dehumidifier | |
| Maintain relative humidity, especially at night when it’s cold outside or when leaving the property unheated – the current dehumidifier is a good brand, but only 12 L capacity. I recommend 20L/Day or even 30/Day and to use it constantly or at least most of the time, including when away (then it should drip into a sink, using the drain provided). Which! recommend: 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 | £280 |
Actions if all else fails | |
|---|---|
| Consider installing a continuous flow bathroom extractor fan | |
| I personally have a few continuous flow extractor fans, and recommend them for all properties with condensation and mould issues, especially lower ground floor flats. The Vent-Axia Silent 7.5W Extractor Fan With Humidistat & Timer Continuous Running, looks good. | £600 |
| Shower panel, sealant and grout checks | |
| As part of an annual check, maintain grout and sealant around the bathroom, especially in the corner by the shower, under the shower screen. Water often leaks out under the shower screen. | £100 |
| Consider using absorption reducing chemicals | |
| For walls above a solid floor such as by the entrance to the bathroom, remove the skirting board at the base of the wall and cut the lowest 10 – 20mm of plaster back to brick. Then run a ~10mm thick bead of Silane/Siloxane thixotropic cream, such as DryZone by Safeguard, along the brick to reduce absorption. Replace the skirting board. This is not instead of other remedial actions. I don’t advocate drilling holes and injecting chemicals, as you could damage the wall. Likewise, I didn’t advocated replacing plaster with slurry, unless you are unable to stop water at its source, which you can by following these recommendations. | £200 |
| Check for gaps and cracks around the stairs above the bathroom. | |
| The under stair rooms, primarily designed for coal storage, in all these Victorian properties, is at risk of penetrating damp from the stair above. A few cracks won’t make much difference, while vapour from the shower is excess. However, once the room dries out, you may find for more permeant dampness. In which case you should fill crack and gaps on the outside with an external caulk for smaller gaps and cement based mortar for larger gaps. | £200 |
| Consider targeted insulation. | |
| There is an argument for keeping the bathroom slightly colder, to reduce the vapour that flows into other rooms. However, consider installing a thermal lining paper, such as wallrock thermal liner or Sempatap thermal solid wall insulation to cold surfaces in the bathroom. | £1,000 |
| Optimal actions – estimate of costs | £2,100 |
I conclude that property suffers from condensation and mould in poorly ventilated bathroom exacerbated by heat loss.
High humidity from shower vapour and heat loss
Advised tenants on vapour reduction and mould control. 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: 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 240108SH0800. I conclude that property suffers from condensation and mould in poorly ventilated bathroom exacerbated by heat loss. 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 240108SH0800
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: Suspected due to water rising; property prone to drive
- Damp treatment: Damp proofed against rising damp
- Weather: Cold, grey, dry
- Property: Lower ground floor flat in an end of terrace Victorian building
- Background: Tenanted property with persistent damp and mould; limited success with dehumidifier
- Changes: Converted into flats; occupants work from home occasionally
- Occupancy: A couple, sometimes working from home
- Mould & notes: Mould present in bathroom
- Primary damp concern: Bathroom and adjacent areas
- Other damp concerns: Dampness in kitchen noticed by tenant
- Compounding: Heat loss under bathroom and stairs
- Airbricks: There is a solid floor no need for air bricks.
- Sub-floor humidity: There appears to be no sub-floor void.
- Tenure: Low, ground floor flat
- Attachment: End of terrace
- Build: Victorian
- Walls: 9-inch thickness
- Exterior comment: Damp visible through interior paintwork
- Penetrating damp assessment: No penetrating damp
- Drains: Not a concern
- Leak signs: Concern noted
- Leak assessment: Not a risk
- Floor: Solid
- Loft: N/A
- Timber assessment: Not a concern
- Last dry: Tenants since August; previous damp issues
- Ventilation assessment: Bathroom extractor fan underperforming; no overrun
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.
