Background
During the sales process, a RICS homebuyer surveyor recommended a PCA qualified surveyor further investigate dampness identified at the base of a front bay wall. Two contractors were chosen by the buyer and seller. Their findings were wildly different, with quotes ranging from £4,000 to £90,000. I, as a PCA qualified damp surveyor with no vested interest, was instructed to carry out an independent survey.
About the damp surveyor
I, Simon Hichens, am PCA qualified as a Certificated Surveyor of Timber & Dampness in Buildings and RICS qualified as an Expert Witness. I choose not to be a member of these associations so that I can focus on the root causes of damp and freely and publicly correct the PCA and its members, if and where necessary.
All surveys are published online, allowing owners and other interested parties to look back at reports years later and confirm findings, or otherwise – although I don’t think there are any significant errors yet, at least as far as inaccurately misdiagnosing the cause of dampness at the base of a wall is concerned.
We act for owners wishing to solve complex damp issues, with only occasional involvement during the sale process.
Data loggers – no data loggers used
In conclusion, from the data loggers
Data loggers help demonstrate whether or not a property is properly ventilated, without which condensation is likely. According to Dew’s Law a property should maintain internal dew points below the external temperature at all times otherwise damp and mould are likely.
Evidence & Illustrations
Watch the online video for a clearer understanding of the RICS survey and contractor quotes.
Groundwater is the water under the water-table. Groundwater is pumped out to about 60M under the ground level in Greater London and other large cities.
The reason why rising damp is defined as the rise of groundwater, is that the water under the water table is saturated and therefore does not percolate down, otherwise water is drawn down by gravity roughly 90% more than up, and the rise of rainwater in soil is only limited. There are many effects that cause rising damp like symptoms, but these are all defects of the property, such as leaking drains and should be dealt with to stop rot and subsidence. I found no internal dampness that could be associated with leaking drains.
To verify rising damp, which is caused by groundwater, you would typically:
- Confirm that the location is at risk of rising damp see above.
- Confirm the present of pumping fixes and cables and avoiding them, drill 1-meter-deep holes at all four corners using a thin, 10mm bit. Insert a thinner, 8mm tube into the holes, seal the holes with a finger, and pull the tube out quickly to check for water. If one tube shows more water than the others on a level surface, it could indicate a nearby damaged drain. If all four tubes show the same water level, it suggests high groundwater, posing a risk of rising damp if the damp-proof course (DPC) is insufficient. None of the surveyors performed this test, and in my view, it was unnecessary as the walls were mostly dry and the location isn’t prone to groundwater.
I did not drill holes to test for rising damp because I could see from the geological map and by checking London bore holes, I could assure myself that there was no risk of rising damp.
The key to solving condensation and mould is follow Dews Law. That is: always keep the internal Dew Point below the external temperature, even at night.
The dampness was high along this section of wall. If there was rising damp, then the meter reading would be high across the whole property. If there was a leaking drain, then the dampness would be highest on the side of the wall closest to the drain, which is on the flank wall side.
There were no brown stains, the tell tale sign of rainwater penetrating through the building (clearly the paint made it hard stop see, but you can normally see browning even on ark paint).
Although I have no direct evidence, there are plenty of risks and tell-tale signs of condensation, made worse by the blocked air vent with no insulation, a sofa blocking the flow of underfloor heating, and a cold sub-floor air brick. A damp wall can take 9 months to dry out, so even though it is likely to have become damp when cold in winter, this section of wall is vulnerable to remain damp all year round.
Insulating the above ground air brick and moving the sofa out, as well as increased use of internal ventilation and dehumidification such that the dew point is never above the external temperature, will solve the condensation risk to this wall.
Risks
To keep the property dry | |
|---|---|
| Use a dehumidifier | |
| Maintain low dew points and 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 | |
| Direct a fan onto the damp patch to speed up the drying process. | |
| Monitor vapour with data loggers | |
| Monitor relative humidity and temperature against the wall. The Dew Point should be kept below the outside temperature at all times, including at night and went away. Use a data logger, such as ORIA Wireless Thermometer Hygrometer (20m (2 Packs)). In addition monitor improvements on the damp wall a pencil line and damp meter such as dr.wood moisture meter, logging improvements each month. | |
| 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 cooking with an extractor fan | |
| use the kitchen extractor fan whenever cooking. Ideally cook with tops on pots and pans, with the heat turned down. | |
| Remedial actions – estimate of costs | £180 |
Actions if all else fails | |
|---|---|
| Consider targeted insulation | |
| I would fill the blocked up airbrick above the floor, behind the sofa, with insulation, such as expanded foam, and cover the front with a cement-based mortar, covered in paint. I would cover the cellar wall with PIR, thermal insulated plasterboard in the cellar and insulate around the cold water pipes, including those entering and existing the cellar. | £1,000 |
| Fill render crack | |
| Check and repair any cracks in the exterior render, plinth and windows sills 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 with an impermeable paint. This should not take more than a few hours and should be achievable with a ladder. | £300 |
| Improve sub-floor ventilation | |
| The ventilation could be improve with a simple screw driver to remove paint from around the sub-floor air brick or grill. I would also measure sub-floor relative humidity with a hygrometer probe or data logger. I would install a fan into the cellar, sucking air from the sub-floor to create flow and reduce the risk of super heated vapour from the warm cellar condensing in the sub-floor void. Use an inline fan, connect to a timer. | £300 |
| Direct downpipe to gullies and drains | |
| Ideally downpipe should flor into a drain. I could not see example of this casing intrnal dampness, however it is a theorectical risk. | £1,000 |
| Optimal actions – estimate of costs | £2,600 |
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 no signs of penetrating damp, that is normally accompanied by brown staining. There were many signs of excess humidity causing condensation.
Most properties have some risk of condensation, especially given modern living and concern about energy consumption. The risk is exacerbated by cold zones such as the blocked air brick to the front, behind the sofa, and sub-floor air brick below.
. By taking a root cause approach, rather than a focus on blocking the symptoms of damp the savings are likely to be around £100,000. This contrasts with typical damp proofing contractor recommendations such as chemical treatment for rising damp and untargeted ventilation, such as PIV systems.
Flood risk: Low 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: remote possibility, see explanation by Dr Robyn Pender of Historic England.
I confirm that I inspected the property on 240703SH1200. 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 no signs of penetrating damp, that is normally accompanied by brown staining. there were many signs of excess humidity. 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 240703SH1200
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.
- Weather: drizzle during survey
- Property: Early 1900
- Background: A RICS surveyor recommended a PCA qualified surveyor investigate. The buyer and seller chose two contractors, their findings were wildly different, so a damp surveyor with no vested interest was instructed to carry out an independent survey.
- Changes: Modernisation, including a rear extension, loft conversation, dry lining, boiler put in cellar and blocked air vents, as well as modern living.
- Occupancy: family
- Mould Colour: no mould
- Primary damp concern: dampness at base of front bay
- Other damp concerns: In cellar
- Compounding: Heat loss caused by blocked front above floor level air vent.
- Airbricks: The air bricks are painted over and the rear is blocked.
- Sub-floor humidity: There is a risk of high sub-floor relative humidity.
- Tenure: house
- Attachment: a semi-detached
- Build: 20th century
- Walls: solid wall made of two brick widths (225mm)
- Exterior comment: There was a render crack, but otherwise 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 suspended timber floor did not feel damaged.
- Loft: The loft has been converted.
- Timber assessment: There are no suspicions of significant timber decay.
- Last dry: It is difficult to know when dampness started, but it is mild and has probably never been seen or of concerned to the owners.
- Ventilation assessment: The ventilation is in place, but whether it is used properly is difficult to know without seen data from data loggers.
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.
