Background
Here the property had structural movement, which was thought to be the cause of damp. Certainly cracks can cause localised penetrating damp, but it was not the root cause of the majority of damp.
Data loggers – to follow
In conclusion, from the data loggers
- To follow
Evidence & Illustrations
Hygroscopic salts
Hygroscopic salts, such as calcium nitrate, often result from the historical burning of coal or equine urine. These salts can absorb and release moisture from the air, maintaining a state of dynamic equilibrium. They are not a source of moisture but often mistaken for and treated as coming from rising damp. The best treatment is to cover the affected area with a non-absorbent layer like an oil-based primer, such as Zinsser Cover stain.
To keep the property dry | |
|---|---|
| Ask neighbour to stop leak | |
| Ask neighbour to find and repair their leak, it may be from the taps, or tiles. Grout and bathroom sealant should be checked for gaps and cracks annually. | |
| Reduce vapour from cooking | |
| Cook with tops on pots and pans to reduce the production of vapour from cooking by 80%. | |
| 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 |
| 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. | |
| 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. | |
| 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. | £500 |
| 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. | |
| 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 |
| Monitor sub-floor humidity | |
| Use a hygrometer to measure relative humidity in the cellar and sub-floor. A probe can be pushed through gaps in the areas not accessible from the cellar. The sub-floor relative humidity will fluctuate. If it remains above 85%RH for an extended period then consider installing a fan into the sub-floor to blow air out. Increasing ventilation is tricky as there is limited accessibility. A company called ELTA made a Sub-Floor Ventilation Fan, which many clients with similar issues have installed with success, but ELTA have been closed down. This site seems to offer the same unit: https://www.builders-superstore.co.uk/product/ventilation-fan-sub-floor-mains-powered/ | £10 |
| Fill gap outside first floor window | |
| I would replace the cement-based mortar and any gap in the window sill. | £100 |
| Remedial actions – estimate of costs | £814 |
Actions if all else fails | |
|---|---|
| Duct out kitchen extractor fan | |
| The main issue to getting ducting out the extractor fan is hiding the ducting. 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 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 |
| Repair or replace bathroom extractor | |
| Consider installing a continuous flow bathroom extractor fan such as Brookvent Airstream DMEV 100 HT (Continuous Running Extractor Fan with Humidistat 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. | £400 |
| Hygroscopic salts | |
| In the front bedroom chimney breast, there appears to be a zone of condensation like damp. While it could be standard condensation, I think it may be caused by hygroscopic salts, which 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 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 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 | £1,150 |
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. The brown patch is caused by your neighbour’s bathroom. There were many signs of excess humidity causing condensation.
The neighbour’s shower is insufficiently sealed. The grout and sealant should be repaired and then checked annually.
I improved the bathroom extractor fan. 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 240221SH1000. 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. the brown patch is caused by your neighbour’s bathroom. there were many signs of 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 240221SH1000
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: Despite the low risk of rising damp, disruption at the base of external walls suggests there has been an attempt at chemical treatment against rising damp. Internal plaster may have been 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.
- Weather: dry overcast
- Property: Victorian
- Background: The property has recently suffered from settlement to the front, exposing areas of dampness.
- Changes: neighbour property converted to flats and lifestyle changes including more frequent showers and clothes washing, including greater occupancy during the Covid pandemic.
- Occupancy: owner occupied
- Mould Colour: brown stain next to neighbour’s bathroom
- Primary damp concern: a brown stain half way up party wall
- Other damp concerns: dampness mainly around kitchen
- Compounding: poor ventilation
- Airbricks: Condensation was forming on bricks in the cellar.
- Sub-floor humidity: Air in the sub-floor void was humid. Consider installing a sub-floor extraction fan.
- Tenure: house
- Attachment: a terraced
- Build: Victorian
- Walls: solid wall made of two brick widths (225mm)
- 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: The loft was not of special concern.
- Timber assessment: There is a risk of rot in the cellar and sub-floor void.
- Last dry: I understand that some damp issues were picked up when you bought, but these have become worse over time.
- Ventilation assessment: There is no ducting out of the property from the kitchen extractor fan and the bathroom fan was running slowly, I have improved it.
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.
