Background
In November 2022, residents of a ground-floor Victorian flat in Sydenham faced significant damp challenges. Initially identified as ‘rising damp’, extensive measures including wall rerendering and damp proof course (DPC) installation were undertaken. Concurrently, a Positive Input Ventilation (PIV) system was recommended for the bedroom to address condensation-related dampness and mould. However, the persistence of condensation, alongside concerns regarding the chimney breast and uneven floor temperatures, suggested a more complex issue. This survey investigates these multifaceted damp problems, focusing on the effectiveness of previous interventions and identifying the true extent of damp penetration, exacerbated by hygroscopic salts and uneven insulation.
Data loggers
In conclusion, from the data loggers
- I would run a 20 l/day dehumidifier 24/7 and continuous flow bathroom extractor fan, with door closed, and be careful to cook with tops on pots and pans, ventilating whenever cooking.
- You asked about placing a PIV vent unit in the bedroom. While they could reduce the internal vapour, it is a very energy and CO2 inefficient way of doing that, compared to targeted ventilation, like bathroom extractor and a dehumidifier. The reason is that a) PIV units blow in cold air with external dew points, but only replacing averagely humid air, so can never beat targeted ventilation, like a bathroom or kitchen. Comparing the dehumidifier to PIV system, there is no wasted energy. All the energy consumed in removing vapour from air is released as heat, with a roughly 50% bonus from entropy, like an air source heat pump.
Evidence & Illustrations
The cold solid floor is impermeable, this will amplify condensation that forms on the cold floor. Timber can be seen to have rotted and nails rusted. Plaster should not touch a solid floor to reduce the risk of condensation forming on the cold solid floor being absorbed upwards (which is not rising damp, but condensation). While cutting back the last 10mm of plaster and applying a thin run of an absorbent reducing Silane/Siloxane thixotropic cream, such as DryZone by Safeguard would reduce the absorption of condensation, it is not addressing the root cause, which is excess vapour and insulation ventilation and or dehumidification.
To keep the property dry | |
|---|---|
| Fill render cracks | |
| Check and repair any cracks in the exterior walls to prevent water ingress. Address external render cracks by raking out, that is slightly enlarging and removing loose material and filling with an acrylic based caulk for small gaps and cement based mortar for larger gaps over 3mm. Paint over cracks and previously painted cracks with an impermeable paint, such as Zinsser or Dulux external impermeable masonry paint, avoid semi-permeable paints, they don’t stop water entering cracks. This should be done for the whole property. I am assuming two days work, divided. It may cost more if scaffolding or a platform is required. | £500 |
| 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 |
| Use fan to expedite drying | |
| The main area of dampness by the door on the front wall should dry up on its own accord now that the leak has been repaired. Direct a fan towards any damp areas to expedite the drying process. Monitor dampness, once dry, rub away surface salts, they are benign, then paint possibly after using filler or applying finishing plaster. | |
| Monitor improvements | |
| Mark improvements on damp walls with a pencil line or sticky note and use a moisture meter, such as the Dr. Meter Wood Moisture Meter 2 in 1 Pin & Pinless Multifunctional Water Detector £23.99 or similar damp meter, to log and monitor reduction to dampness in walls. By doing so, you will gain early confidence in these recommendations. Use devices like the ORIA Wireless Thermometer Hygrometer to monitor relative humidity and temperature near walls or ceilings, look to keep the dew point at or below the external temperature. The dew point is shown on the app (if not use https://mouldpoint.co.uk to calculate the dew point from humidity and temperature readings). | |
| 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. Don’t use these products on shoes, follow manufacturer’s directions. | £100 |
| Target vapour from clothes drying | |
| Opt for a tumble dryer, dry laundry in a well-ventilated room with the door closed (such as a bathroom with the extractor fan on or window open), or employ a sufficiently high capacity dehumidifier. Avoid drying clothes in poorly ventilated areas and anywhere near cold walls. | |
| Target vapour from cooking | |
| Always use tops on pots and pans to reduce vapour emission by 80% and where applicable use an externally ducted kitchen extractor fan. | |
| Maintain airflow close to cold walls | |
| Ask the tenant to keep objects away from cold walls where condensation or mould has built up, such as the shelf where the shoes are becoming mouldy. Consider insulating cold internal surfaces, for example, with floor insulation from B&Q or Wallrock Thermal Liner (ensure to use Wallrock Thermal Liner Adhesive). | |
| Target insulation | |
| As a minimum I would insulate in the chimney breast and between the large metal pipes under the stairs and wall. It is better to use vapour active insulation, such as Woodfibre, when above timber to reduce the risk of condensation forming within the wall risking rot in timber below, an alternative is thermal insulating lining paper such as Wallrock. | £100 |
| Adjust gutter | |
| Instruct a roofer and or general builder to adjust the gutters so there are no gaps between gutter joins and with the downpipe. Check during a rainstorm for any rainwater leaks. | £200 |
| Remedial actions – estimate of costs | £1,080 |
Actions if all else fails | |
|---|---|
| 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 |
| Consider using absorption reducing chemicals | |
| For walls above a solid floor, 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 and be held responsible for causing damp in your neighbour’s property, with or without the necessary party wall agreement. Likewise, I didn’t advocated replacing plaster with slurry, unless you are unable to stop water at its source. | £200 |
| Optimal actions – estimate of costs | £500 |
I conclude that there was no evidence of rising damp, which comes from groundwater in contact with walls. The risk of groundwater is very low. There were many signs of penetrating damp and excess humidity causing condensation.
there are very thin cracks in the render causing water to penetrate through the wall. There has ben an attempt to insulate the wall, but moisture can pass through the seams.
. 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 240129SH1400. I conclude that there was no evidence of rising damp, which comes from groundwater in contact with walls. the risk of groundwater is very low. there were many signs of penetrating damp and excess humidity causing condensation. 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 240129SH1400
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: A damp proofing contractor claimed your property had 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
- Property: Victorian ground floor flat
- Background: The owners bought in October 2022 and damp proofed around the chimney breast
- Changes: conversion into flats, damp proofing treatment, open plan kitchen with extension, lifestyle changes including more frequent showers and clothes washing, including greater occupancy during the Covid pandemic.
- Occupancy: owner occupied
- Mould & notes: mould around property
- Primary damp concern: dampness in various places including top of bedroom ceiling
- Compounding: hygroscopic salts around chimney
- Airbricks: There is no reason to be concerned about the sub-floor ventilation.
- Sub-floor humidity: The sub-floor had normal levels of relative humidity.
- Tenure: flat
- Attachment: a semi-detached
- Build: Victorian
- Walls: solid wall made of two brick widths (225mm)
- Exterior comment: There are render cracks and gaps.
- Penetrating damp assessment: Internal dampness lined up with external water marks, therefore we conclude that penetrating damp, or heat loss caused by rainwater is a factor in the internal dampness.
- 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 suspended timber floor did not feel damaged.
- Loft: There was no loft.
- Timber assessment: There are no suspicions of significant timber decay.
- Last dry: I understand that some damp issues were picked up when you bought, but these have become worse over time.
- Ventilation assessment: The bathroom ventilation stopped working a few weeks ago, you should replace the fan and keep the window open in the meantime, always keep the door closed.
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.
