Open – Print or Save PDF – Refresh
Data loggers
In conclusion from the data loggers
- During the period under investigation the surface relative humidity in the cellar (green dotted line) is high, peaking at 100%RH and condensing on the coldest surfaces. Relative humidity is at risk of condensation above the damp proof course, thereby circumventing it.
- The surface relative humidity is calculated considering the temperature difference between the data logger and cold surface at the time of the survey – this is an approximation and illustrative. You can check the difference more accurately with a laser thermometer on a cold night to update the interface tab in the spreadsheet.
- For each -1°C the relative humidity will be about 5%RH higher. The effect increases as the temperature difference between inside and outside increases such as when it’s cold.
- The grey line in the graph is called the dew point differential. It tells me that excess vapour is evaporating off the cellar floor compared to the kitchen. In most cases it is useful data, but not here as the cellar is effectively isolated from the kitchen. They will have no influence on each other.
- It is interesting that the dew point (which rises and falls with quantity of vapour in the air) and the temperature is very stable despite fluctuating external (thick transparent pink and light blue). This illustrates dynamic equilibrium, condensation release heat, conversely evaporation absorbs it. This is why cellars are good for storing wine long term.
- The example property dew point is in fact from my house, where I run a dehumidifier to maintain a healthy environment and reduce the need for and cost of heating. You should aim to bring your dew points down to a level closer to the outside, which in winter will be around 12°C. Increase the use of ventilation and consider getting a dehumidifier, to see improvements.
While I don’t think the root cause of moisture in your cellar is condensation, it think its made much worse by insufficient sub-floor ventilation and likewise there is insufficient ventilation inside the house. Data loggers will be useful for ongoing monitoring following the implementation of my recommended actions. Working from home results in more cooking and more respiration. The energy crisis has resulted in people turning down the heat in unoccupied rooms and closing vents and windows. Risk can be reduced with a 20L+ dehumidifier.
Evidence & Illustrations
Property type: The property is a mid terraced 1930’s 2 storey house with solid brick construction and suspended timber floor over a sub-floor void.
Background summary:
Your main concern:
You were concerned about “paying for the driveway to be redone or brickwork underground outside to be repointed if it’s not necessary at this moment. Nor do we want to pay for multiple professionals to come investigate if not necessary.”
A simple answer is: No, I don’t think you need a new driveway, just an Aco drain connected to the front rainwater drain and for the Aco drain to extend perpendicularly onto the parts of the drive where ponding has occurred.
This surveys demonstrates the importance of having an independent surveyor who doesn’t benefit from recommendations.
The sub-floor ventilation is insufficient, as can be seen by the way the spiders are happy building nests. The sub-floor ventilation was probably never very good, at least not when considering the topography and local ground drainage.
While this is the most likely cause of the water under the floor, it is also possible that the rainwater drain is leaking underground. I would anyway remove the stop end and connect the Aco drain to the rainwater drain. Give it a month or so and heavy rain to see if the sub-floor dries out. If not consider having a CCTV drain survey and repair, if required. Then solve the sub-floor ventilation, which should be done anyway, but not before knowing if the Aco is the solution.
The thermal lens, where blue is about 5°C colder than yellow, highlights areas of heat loss. There is natural heat loss in the corner of the room and under the eaves.
Remedial actions necessary to keep the property dry | |
|---|---|
Connect Aco drain to rainwater drain | |
| While this is the most likely cause of the water under the floor, it is also possible that the rainwater drain is leaking underground. I would anyway remove the stop end and connect the Aco drain to the rainwater drain. Give it a month or so and heavy rain to see if the sub-floor dries out. If not consider having a CCTV drain survey and repair, if required. Then solve the sub-floor ventilation, which should be done anyway, but not before knowing if the Aco is the solution. Also I would wait for heavy rain fall, or throw buckets of water on the drive, to identify the deepest point. Mark the deep point of any area where there is ponding and have the Aco drains extended to the centre of the ponding. | £200 |
Monitor sub-floor humidity | |
| Use a data logger in 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/ | £300 |
Minimise 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. | |
Minimise vapour from cooking | |
| TIP: Cook with lids on pots and pans to reduce the production of vapour from cooking by 80%. Keep the kitchen door closed. | |
Minimise vapour from drying clothes | |
| TIP: Dry clothes outside, 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. | |
Keep some late night heat | |
| TIP: Maintain a small amount of heat late at night when it’s cold outside. More efficient alternatives include 1) insulating cold walls, 2) strategically placing one or more dehumidifiers, positioned where the night-time dew point is highest – use data loggers to locate the optimal position (typically a damp room near a damp wall, e.g., kitchen, bathroom). Personally, I run a dehumidifier whenever leaving a room unheated. | |
Encourage flow of warm air currents | |
| TIP: Keep objects away from walls where condensation or mould has built up. Consider insulating cold internal surfaces, for example, with floor insulation from B&Q or Wallrock Thermal Liner (ensure to use Wallrock Thermal Liner Adhesive). | |
Monitor humidity | |
| 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)) – see surveyor.tips/datalogger – in place. Monitor damp with a simple conductance damp meter, logging improvements each month. | |
Paint external render cracks | |
| Address external render cracks by repainting damaged or cracked render with at least two coats of impermeable paint like Zinsser or Dulux external masonry paint. | £100 |
Remedial actions – estimate of costs | £600 |
Optimal actions to help remain damp free (if all esle fails) | |
|---|---|
Reduce drive ponding | |
| Consider raising the driveway so that water does not pond. Alternatively, consider running connecting Aco drains, see first recommendation. | £200 |
Reduce damp penetrating at base of wall | |
| Run a fillet of a triangular cement-based mortar, along the wall base of the external wall, front and rear wall, to reduce the rainwater able to seep into the cellar (sub-floor). | £200 |
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. | £200 |
Use a dehumidifier | |
| Maintain relative humidity, especially at night when it’s cold outside or you are maintaining lower temperatures downstairs compared to upstairs a night is easiest done 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. | £180 |
Target insulation | |
| As a minimum I would insulate the loft into the eaves, with modern insulated loft insulation 300m double pile (one layer crossing over the other layer). Also insulate behind the radiator and the radiator pipes and cold water and hot water pipes. You can expect energy savings of approximately 5% – 10% p.a. for the first £1,000 to £2,000 spent by being selective in your approach. This recommendation serves as a starting point for discussion. You should assess whether this approach aligns with your financial and practical needs. | £1,000 |
Consider installing kitchen ducting | |
| If this were my property, I would install rigid ducting from the current kitchen extractor fan to the outside (test airflow with a piece of A4 paper it should blow more or less horizontally out). | |
Consider installing a 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. | £500 |
Remedial actions – estimate of total costs | £2,280 |
I conclude that no evidence of rising damp, which comes from groundwater in contact with walls. The risk of groundwater is very low. Water is not draining through the Aco draining from the drive way. There were many signs of excess humidity causing condensation and mould.
The Aco drain is not connected to the rainwater drain, which is the most probable root cause. Other possible factors could be ponding or damage to the rainwater pipe. Moreover, there is inadequate sub-floor ventilation. The habitable space is affected by this lack of ventilation and areas of poor insulation, such as eaves.
I cleared the cobwebs from the bathroom extractor fan; it is now operational, though it requires manual switching. By taking a root cause approach, rather than a focus on blocking the symptoms of damp the savings are likely to be around £10,000. This contrasts with typical damp proofing contractor recommendations such as chemical treatment for rising damp and untargeted ventilation, such as PIV systems.
Flood risk: 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 Damprisk of rising damp is remote, see explanation by Dr Robyn Pender of Historic England.
I confirm that I inspected the property on 25 September 2023. I conclude that no evidence of rising damp, which comes from groundwater in contact with walls. The risk of groundwater is very low. Water is not draining through the Aco draining from the drive way. There were many signs of excess humidity causing condensation and mould. 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 dataloggers for example the Smart Hygrometer measuring humidity on the wall and nearest source of vapour, before and after following our recommendations. These dataloggers 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 25 September 2023
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.
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.
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.
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 (the ceond in aseries won’t add as much)
- 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 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 dehumidifer or window open, never on radiators or heated rail without a door closed and 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.
Relevant examples of properties with similar damp issues: electric-sockets
Try the A.I. agent above, for example write in the text entry:
Summarise the root causes of damp and recommended solutions
– Write anonymously, as text is saved and sample checked for accuracy.
– Our AI uses Chat GPT 4, we can’t guarantee accuracy of AI responses.