Data loggers
In conclusion, from the data loggers
- The green dotted line shows the surface relative humidity it is illustrative based on the temperature difference between the logger and damp wall at the time of the survey. Condensation could be seen on cold water pipe.
- The blue line shows the dew point and light blue line the external dew point. Dew points are a proxy for vapour quantity, exactly matching each other. You are running a dehumidifier. The benefit can be seen in the difference between the two blues lines towards 20 November.
- I would keep running one of more powerful dehumidifiers and consider adding a fan to speed up the drying process.
Evidence & Illustrations
Background – when you purchased the flat you had advice from an damp proofing contractor, which in summary was:
Issues and Risks: The inspection identified several issues: externally, high ground levels relative to the internal floor, a need for repointing the rear garden wall, a suspected leak in the rainwater gutter, and a missing stop end on a gutter. Internally, in the basement, there’s visible dampness on walls with high moisture readings, attributed to lateral moisture penetration and hygroscopic plaster. Similarly, the ground floor shows high damp readings, with potential rising dampness in the bathroom area, exacerbated by external moisture penetration and hygroscopic plaster.
[Damaged pointing is rarely the cause of internal dampness and was not here. I did not see a suspected leak from a gutter or missing stop end. It may have been repaired. I did not see any hygroscopic salts, while also a sign of rising damp, they normally come from historic use of coal and are best treated with an impermeable layer, such as PIR. There was no evidence or risk of rising damp.]
Remedial Actions and Guarantees: To address these issues, the following remedial actions are recommended: installing a cavity drain damp proof membrane with a drainage channel and pump system in the basement, and inserting a chemical damp proof course in the ground floor area, accompanied by waterproof plastering. The client is responsible for preparatory works like clearing the gully and repointing walls. Guarantees include a 10-year guarantee against rising dampness for injected walls, a 5-year guarantee for the ground floor waterproof render system, and a 30-year product plus 5-year installation guarantee for the membrane system. I understand the cost was in the order of £60,000.
[I believe you can achieve a better result, lower risk, provide good insulation, better ventilation and last longer at about 1/3 of the cost, but you should understand the causes of damp, the risks and features of the different materials.]
There is a new material called Aerogel, which inhibits water, but allows vapour to pass through it, it can also be adhered to a brick wall with Insta-stik foam, without need for battens. It is more or less as good an insulator as PIR, but at a fraction of the width, so especially good for thin areas, such as reveals around windows. The downside is the cost at around £50 per sq m 2, which makes it roughly five times as expensive as the equivalent 30mm rigid board insulation. So to be clear, I would recommend Aerogel throughout, but am suggesting a pragmatic solution to keep costs down. In this case you could use PIR taped together with carefully with foil, following manufacturers guidance. Allow some weeping of water onto the bench at the base of the wall. You can cover this with MDF, but may occasionally have to replace sections of MDF if it becomes damp.
Insulation goes beyond the normal damp survey. However, I see many examples of poorly designed and installed insulation where thermal bridging has resulted in mould and condensationand risk of rot. The risk of rot comes from condensation forming within the now cold wall. Therefore internal insulation should be vapour active to evaporate condensation evenly away from brick or stone wall, when above timber or in your case near timber.
In my opinion a continuous flow bathroom extractor fan with trickle vents in the downstair windows, will better target the production of vapour, make sure to keep the bathroom door closed and use a dehumidifier whenever drying clothes internally. These continuous flow bathroom extractor fans have a boost function when lights are turned on or high humidity is detected.
To keep the property dry | |
|---|---|
| Insulate with plasterboard | |
| I would use PIR, like Celotex or Kingspan, except for the top 100m which should be vapour permeable but water resistant, such as aerogel, see explanation and evidence section above. For clarity, don’t use PIR in the ground floor area where you have timber joist below, it is better to use wood fibre. | £10,000 |
| Ensure vapour barrier | |
| Make sure to you foil to create a vapour barrier around the PIR | £500 |
| Strengthen and monitor timber joist | |
| I would a install a tanalised 1M section of timber to both the final two joists front by party wall, with a least two bolds, probably using joist hangers secured to the front wall. I would leave an access hatch. Check with a damp meters and photo timber every few months especially during a wet period. Make sure to keep access to timber under the stairs down. Allow the area to dry out as much as possible. | £500 |
| Check neighbour’s downpipe | |
| I would ask your neighbour to have their downpipe checked, I suspect that there is an underground leak. A simple solution would be a 2 M horizontal pipe away from the building towards the street, to remove rainwater from the front of the house. | |
| Repair leak | |
| Replace the leaking internal stop cock with a modern, 90° on off type stopcock and insulate around all pipes, hot cold, gas and if relevant electrical cables. Remember that gas pipes may become redundant in a few years time. | £200 |
| Improve bathroom ventilation | |
| Consider installing a continuous flow bathroom extractor fan such as a Vent Axia or Brookvent Airstream DMEV 100 HT (Continuous Running Extractor Fan with Humidistat Timer). A normal light switch acted vent with 30 minute overrun would sufficient upstairs. The reason is that a continous flow extractor fan blows out heated air. The estimate additional annual cost is around £100. Make sure to have trickle vents in the downstair rooms. | £500 |
| Reduce vapour from cooking | |
| Cook with tops on pots and pans to reduce the production of vapour from cooking by 80%. | |
| 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. | |
| Use fan to expedite drying | |
| Direct a fan onto the damp patch to speed up the drying process. | £50 |
| Repair 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 with impermeable paint such as Dulux or Zinsser impermeable masonry paint. Finish the base of the wall with a cement based fillet of mortar. | £100 |
| Remedial actions – estimate of costs | £11,850 |
Actions if all else fails | |
|---|---|
| Consider installing a kitchen extractor | |
| The main issue to getting ducting out the extractor fan. 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. | £300 |
| 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). | |
| Optimal actions – estimate of costs | £300 |
I conclude that penetrating damp on lower ground floor, use thermal insulating plasterboard with vapour barrier, ensure ventilation.
Need to manage vapour due to habitable space reducing natural evaporation of rainwater below soil
. By taking a root cause approach, rather than a focus on blocking the symptoms of damp the savings are likely to be around £20,000. 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: Near low productive aquifer with intergranular flow See British Geological Survey.
Therefore risk of Rising Damp: highly unlikely, see explanation by Dr Robyn Pender of Historic England.
I confirm that I inspected the property on 231113SH0800. I conclude that penetrating damp on lower ground floor, use thermal insulating plasterboard with vapour barrier, ensure ventilation. 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 231113SH0800
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: Concern about rising damp following a damp proofer survey
- Damp treatment: Damp proofing treatment with injections and internal plaster replacement
- Weather: Dry but had rained
- Property: Victorian ground flat with plans to make the lower ground floor habitable
- Background: Purchased a year or two ago, lower ground used as music studio, now damp
- Changes: Converted into flats, lower ground was a cellar, no extractor fans in bathroom and kitchen
- Occupancy: A couple often working from home
- Mould & notes: Signs of mould on ground floor near socket.
- Primary damp concern: Penetrating damp through lower ground floor walls
- Other damp concerns: Dampness and mould on first floor near kitchen and bathroom
- Compounding: Heat loss, damaged render outside
- Airbricks: Not relevant
- Sub-floor humidity: High, walls very wet
- Tenure: Flat
- Attachment: Semi-detached with side access of left
- Build: Victorian
- Walls: 9 inch thick
- Exterior comment: Signs of water ingress from neighbour’s downpipe
- Penetrating damp assessment: Clear penetrating damp into lower ground floor
- Drains: No issues
- Leak signs: Leak from internal mainswater stopcock
- Leak assessment: There was a minor leak from the stopcock it does not account for the damp in the basement
- Floor: Suspended timber over lower ground, solid floor in lower ground
- Loft: Not applicable
- Timber assessment: Signs of cellar rot and woodworm
- Last dry: Dampness in lower ground floor probably longer term from penetrating damp
- Ventilation assessment: No ventilation downstairs or in kitchen and bathroom, internal clothes drying
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.
