“If the only tool you have is a hammer, it is tempting to treat everything as if it were a nail.”
This aptly describes a situation where professionals with a limited set of skills may misapply their tools to a wide range of problems. In the context of damp proofing, practitioners skilled primarily in applying damp proofing creams and impermeable slurry are often inclined to diagnose various forms of dampness at the base of a wall as rising damp. This approach can lead to misdiagnoses, as the actual causes of damp—such as condensation, penetrating damp, or leakage—require different solutions. The reliance on a singular method, regardless of the damp’s origin, underscores the need for a comprehensive diagnostic process. Identifying the correct cause of damp ensures that the appropriate, effective treatment is applied, avoiding unnecessary costs and ineffective results – see discussion on damp proofing treatment.
Law of the instrument – Abraham Maslow 1966
Background
In a Victorian property, dampness and paint discolouration ranging from the skirting board up to 1 metre on the wall, with varying tactile sensations of dampness and dryness. Notably, a contractor’s damp detector signalled readings above 60, suggesting rising damp as the culprit requiring injection treatments. Adjacent findings included damp yet visually dry plaster beneath peeled lining paper and a small patch of flaky paint without evident moisture. Furthermore, the kitchen area, previously external prior to extension, exhibited flaky, bubbling paint with reported high damp readings. This scenario underscores the challenge of diagnosing damp in aged properties, compounded by structural modifications and historical repairs.
Data loggers
In conclusion, from the data loggers
- Make sure to use the kitchen extractor fan, cook with tops on pots and pans and run a dehumidifier.
- Keep the bathroom extractor fan running for at least 30 minutes after taking a shower, with the door closed. Consider running it for most of the day.
- Dry clothes outside on in a vented room or dryer, but also use a 20 litre per day, dehumidifier.
Evidence & Illustrations
To keep the property dry | |
|---|---|
| Reduce vapour from cooking | |
| Cook with tops on pots and pans to reduce the production of vapour from cooking by 80%. The kitchen extractor fan ducting is in place, make sure to use it whenever cooking. | |
| Use a dehumidifier | |
| Maintain dew points at or below external temperature, with a dehumidifier, given the issues and speed requirement, I would use a 30+ per day pro breeze (I have one, they are a little noisy), otherwise a 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 | |
| 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. While there is no legal requirement to provide drying facilities for tenants, think of a good solution, which could include a drying rack in the bathroom or probably better a dehumidifier with instructions to always use it when drying clothe or internal humidity and or dew points are too high. | |
| Bathroom Humidity Management | |
| After showering, keep the bathroom door closed and the window open or fan running for at least 30 minutes to allow vapour to dissipate. | |
| 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. | |
| Insulate pipes | |
| Insulate around all water pipes, especially cold water, also consider insulating the wall under the cupboard and behind the kitchen units. | £10 |
| Target insulation | |
| I would insulate the kitchen walls behind the units and where the plasterers beading has rusted. I would ask to put radiator insulation foil behind your neighbour’s radiator and tell her about the effects of slight temperature drop causes by radiators when not in use, causing condensation on her side of the wall. | £1,000 |
| Remedial actions – estimate of costs | £1,190 |
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. | £400 |
| Other smallish jobs | |
| I would repair the rear pipe so that it doesn’t leak, fill and or repaint exterior coating such as to the rear, with an impermeable paint, check to see whether the rainwater is splashing from, creating the green on the left, near the left-hand neighbour, and remediate. Fill in any gaps to the front masonry with a cement based mortar. | £150 |
| Hygroscopic salts | |
| I suspect that the wall by the chimney has hygroscopic salts, a form of condensation. You won’t know until you have dropped the dew point for many weeks to see if that will remove the damp look. If not you have hygroscopic salts. Hygroscopic salts may resemble grease stains but rest assured, they’re harmless. They don’t cause damage or mould, yet can appear unsightly, especially during summer heatwaves, potentially complicating property sales or rentals. Keep this report handy to reassure prospective buyers of their benign nature. Effective Solutions: The prime method to conceal these salts involves an impermeable blocker with at least 300mm overlap, preventing the spread of any damp appearance. Aim for a uniform treatment across wall sections to ensure consistent humidity interaction. Remember, these salts often lurk just below the surface. Cost-Effective Remediation Methods: Zinsser B.I.N. Cover Stain: The simplest, most affordable approach. Two coats of this solvent-based primer-sealer should do the trick, costing about £15 plus potential labour. It’s user-friendly, easy to remove and reapply, making it ideal for DIY fixes. For larger areas, consider a gloss paint layer between two Zinsser coats for uniformity. This is a homeowner-friendly task but can also be efficiently tackled by a builder as part of a bigger project. Sempatap/Wallrock: Ideal for mildly cold walls, this lining paper creates a barrier, offering slight insulation. It’s a half-day job costing about £100 per linear metre. Thermal Insulating Plasterboard: For very cold walls, removing plaster and installing this board with a vapour barrier is best, mirroring professional damp proofing. It’s a day-long task, costing around £400 per linear metre. Note on Damp Proofing Slurry: Often less effective, as it can activate salts, it’s also invasive and costly. Starting Point: Zinsser B.I.N. Cover Stain is your go-to. It’s budget-friendly and effective for immediate action, with the option to escalate to plasterboard installation if necessary. Humidity Management: Excessive humidity can highlight salts at the impermeable material’s edge. If this happens, a second Zinsser application is recommended. | £50 |
| Optimal actions – estimate of costs | £600 |
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 excess humidity causing condensation and there is some penetrating damp to the front and a risk to the rear and possibility of hygroscopic salts (a form of condensation).
The previous damp proofing treatment has not addressed the roto cause of dampness, condensation from insufficient ventilation.
I double the speed of the bathroom extractor fan, but consider a continuous flow bathroom extractor. 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 240131SH1000. 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 excess humidity causing condensation and there is some penetrating damp to the front and a risk to the r. 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 240131SH1000
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
- Background: Previously damp proofed, damp ha s returned, considering preparing the property for sale.
- Changes: damp proofing, kitchen extension, opened to living room, downstairs bathroom, modern living including hot showers more often than Victorian’s bathed and higher occupancy since Covid.
- Occupancy: owner occupied
- Primary damp concern: dampness around kitchen
- Other damp concerns: dampness around front wall
- Compounding: heat loss from insufficient insulation
- Airbricks: The sub-floor vents have been painted in to the front and through flow reduced below the kitchen extension
- Sub-floor humidity: The sub-floor had normal levels of relative humidity.
- Tenure: house
- Attachment: a terraced
- Build: Victorian
- Walls: solid wall made of two brick widths (225mm)
- Exterior comment: The are some external coating issues that should be dealt with, but they are not the root cause of internal damp.
- 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: The loft was not of special concern.
- 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 kitchen extractor fan ducting is in place, make sure to use it whenever cooking. The bathroom ventilation needed improvement.
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.
