Data loggers
In conclusion, from the data loggers
- During the period under investigation the surface relative humidity on the damp wall (green line) is marginally below the mould risk of 85%RH, but the outside temperature has been mild.
- The grey line is the dew point differential. Dew point is a proxy for vapour quantity. The line shows that vapour is coming from the shower room relative to the living room.
- The dew points are more or less in line with external dew points, suggesting overall reasonable ventilation, however a strong dehumidifier would go a long way to improving internal relative humidity further.
- The example property’s dew point is, in fact, from my house, where I run a dehumidifier. Although I am missing my data from 4 November, I can see you are dropping below my and external dew points, which can only be done with a dehumidifier.
See https://damp.ai/glossary/monitor-humidity-with-data-loggers/ on how to use the data logger app. To work out the external dew point, you can install a logger outside and look at the dew points indicated on the logger app (for example SensorBlue), or as a rough guide if you pick up the Met Weather, look up your area, then take the external temperature and external relative humidity then take off 1° for each 5% below 100%RH to estimate the dew point. So for instance if the external temperature is 14°C and humidity 80%, as a rough calculation, the external dew point is about 14-(100-80)/5 = 10°C.
Evidence & Illustrations
You are considering removing the sections of wall and insulating with EWI insulation. I would seek advice from a structural engineer before considering structural alternations. The walls may not be as tightly tied without the additional section of supporting wall, compared to the normal corner of a building.
EWI is good, but expensive, you can often achieve roughly half the heat loss for say 10% of the cost, by using a dehumidifier and targeting areas of greatest heat loss. This could includ filling in render cracks and damaged paintwork and insulating the wall left by the bomb damage, either inside of outside. Here are some additional areas of heat loss.
To keep the property dry | |
|---|---|
| Target insulation | |
| As a minimum I would insulate the insides of cold zones such as the flank wall and eaves such as with thermal insulating lining paper, with insulation on both sides of the corner i.e. front and rear as well as flank wall. I would also cut off the Frank Schrijver damp proofing rectangular devices at the base of the walls, filling with a small amount of expandable foam for insulation and a cement based mortar to reduce heat loss. I would say, with a dehumidifier, which allows you to reduce the temperature for the same feeling of comfort, you will reduce the heat loss by about 50% by EWI alone, but for a fraction of the price of EWI. Also, the key zone around the coving and front and rear corners will continue to be cold with EWI, if you don’t compensate for these “thermal bridges” with internal insulation. | £2,000 |
| 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 |
| Fill render crack | |
| Check and repair any cracks in the exterior walls to prevent water ingress, whether or not you apply EWI. 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. | £300 |
| Repaint external wall | |
| Wire brush the damaged paint on the external walls back to brick, as much as possible at least to remove the surface salts. Then use a paint that is as impermeable, ideally the same as the existing paint, or more impermeable, such as Zinsser or Dulux external masonry paint. The £1,000 is an approximation, based on three days, work, but depends on how much repainting you undertake and need for scaffolding. | £1,000 |
| Use fan to expedite drying | |
| Direct a fan onto the damp wall to speed up the drying process. | |
| 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. | £100 |
| 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. | |
| Reduce vapour from cooking | |
| Cook with tops on pots and pans to reduce the production of vapour from cooking by 80%. | |
| 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. | |
| Monitor sub-floor humidity | |
| Use a hygrometer to determine the sub-floor relative humidity. It 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/ | |
| Remedial actions – estimate of costs | £3,580 |
Actions if all else fails | |
|---|---|
| Consider installing a bathroom extractor fan with 30 minute overrun after lights are switched off. | |
| 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. I would also install a bathroom spring to encourage tenants to keep the door closed. Ideally the ducting should be rigid, for reduced air resistance, and insulated to reduce risk of condensation in pipe. | £500 |
| Consider installing a kitchen extractor fan ducted out | |
| 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. | £200 |
| Optimal actions – estimate of costs | £700 |
I conclude that primary cause of damp is condensation from excess heat loss..
The main issue is heat loss because the wall was not designed to be an exterior wall, and the extra section of wall to the front is acting as a thermal bridge, drawing heat out. The open nature of the downstairs rooms makes ventilation challenging. Drying clothes internally, especially on a heated drying rack, accelerates the process of moving water from clothes to cold walls. The kitchen extractor fan is not vented out, there is no 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 £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: 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 231027:08. I conclude that primary cause of damp is condensation from excess heat loss.. 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 231027:08
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: Past damp proofing treatment, Frank Schrijver method, and wall injections and slurry, all of which exacerbate heat loss.
- Weather: Fog, 17°C 99% relative humidity.
- Property: Originally a Victorian terrace property, now end of terrace following bomb damage.
- Background: Owner considering thermal external wall insulation, removing part of the additional section of wall for extra driveway, double glazing, and MVHR (Mechanical Ventilation with Heat Recovery) system.
- Changes: Bomb damage, damp proofing treatment, including Schrijver Dutch method, open plan, and extension to rear of property.
- Occupancy: Family
- Mould & notes: Mould especially around cold sockets.
- Primary damp concern: Dampness along flank wall.
- Other damp concerns: Damp near wall of plants.
- Compounding: Heat loss from sections of wall remaining from the bomb damage, particularly to the front, and rainwater damaged front paintwork.
- Airbricks: The rear sub-floor air bricks are inadequate.
- Sub-floor humidity: Air in the sub-floor void was humid. Consider installing a sub-floor extraction fan.
- Tenure: house
- Attachment: an end of terrace
- Build: Victorian
- Walls: 9 inch.
- Exterior comment: Rainwater damage to front paintwork and render cracks.
- Penetrating damp assessment: No signs of water penetrating the whole way through.
- Drains: Of no concern.
- Leak signs: No signs of a leak.
- Leak assessment: There are no obvious signs of a significant mains or wastewater leak.
- Floor: Suspended timber floor to front.
- Loft: Not checked.
- Timber assessment: There are no suspicions of significant timber decay.
- Last dry: Understand the family purchased the property relatively recently, and the issues have arisen since COVID and the energy crisis last year.
- Ventilation assessment: There is insufficient mechanical ventilation.
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.
RICS, PCA, HISTORIC ENGLAND JPS REPORT
RICS (Royal Institute of Chartered Surveyors), Historic England (a public trust protecting sites of historic interest) and the Property Care Association (an association of mainly damp proofers) set out a Joint Position Statement (JPS), in September 2022 – see below.There has long been disagreement about the causes of damp amongst surveyors. Historic England surveyors represent one extreme. They typically do not believe rising damp is a likely cause of internal dampness and rarely recommend altering walls to alleviate damp. By contrast PCA surveyors typically recommend rising damp treatment whenever they see dampness at the base of a wall and often recommend altering a building. RICS surveyors tend to be somewhere near the centre of these extremes. However, unlike Historic England and PCA surveyors, they rarely specialise in damp and often refer issues to PCA surveyors. We and most other independent surveyors are more closely aligned with Historic England’s position except that we are perhaps more pragmatic. For example, if a hole in the wall is the optimum way of solving internal dampness, then we will recommend it, but not otherwise.
JPS questions and answers
In addition to the content typically included in a professional and impartial survey report (e.g. client, surveyor and property details; limitations and exclusions), the report should include the following information:1 A summary of the surveyor’s observations, including an Assessment of Significance.
Condensation and mould around cold areas.
2 The importance of regular building maintenance and how a lack of even basic maintenance can lead to problems arising. This is especially important and relevant to roofs, gutters, hidden gutters, rainwater disposal and changes in external ground levels.
As is common with all buildings, gutters and other rainwater goods should be checked twice annually, ideally during or soon after a rainstorm, for evidence of overflow and rain not being dispersed properly from the property. You should also check that there is no flow of water flow during periods of absence for signs of a leak, for instance, by note the number on the mains water meter outside your house. The paintwork needs to be brushed off and repainted with an impermeable paint.
3 An impartial diagnosis of the damp problem, which should be clearly explained and laid out systematically to communicate the relevant risks to the reader.
Condensation and risk of rot in the sub-floor void.
4 Where recommendations for the repair and recovery of moisture-affected structures are stated, the solutions should be clearly explained and prioritised as appropriate.
The solutions are explained in the Recommendations section. The primary recommendation is Insulation, dehumidifier, continuous flow bathroom extractor fan, repainting external wall with the same or, if unknown, an impermeable paint.
5 The client should be provided with alternative options for which each recommendation should include advantages and disadvantages and the relevant cost and time implications.
This question is primarily directed at PCA damp proofers, to encourage them to consider methods that address the source of water not just the symptoms, such as by hacking off plaster and replacing it with slurry. You can sometimes take this damp proofing approach with short-term success. However, water will eventually find its way through. Furthermore, treatment is disruptive resulting in high cost and a poor finish, with no worthwhile guarantee of success. It likely to lower the value of the property. In our opinion you are better off trying to stop the water at its source, as we recommend. ”
6 Where monitoring and staged interventions are appropriate or beneficial, the client should be informed of the reasons for these options, together with the likely cost and time implications of such recovery strategies.
Properties should be monitored for humidity and temperature using data loggers, see datalogger section of this report. The cost of data loggers is currently less than £20 for two, aim to keep the dew point, as shown on the app screen of each logger (bottom centre on the SensorBlue), within 3°C of the external temperature, especially at night (use ventilation and/or dehumidification to reduce the internal dew point – measure external conditions or refer to weather forecasts for night-time temperatures, such as BBC Weather – a short explanation is; that this will make sure the relative humidity of all surfaces will be below the mould point even if poorly insulated). We also suggest noting values monthly using a multi-functional radio wave and conductance damp meter costing about £24 to monitor and map damp patches on internal walls. This way you can monitoring the dry progress, which typically takes 1 month per 25mm thickness of walls and more if coated. This helps determine if the root cause has been fixed or there is an additional or new source of water, and therefore more actions are required. Ideally this should be started before or soon after starting our recommendations and for about a year, repeating monthly to check progress.
7 Where appropriate, clearly state whether the building concerned represents a financial risk to the buyer or lender and why.
8 Any conflicts of interest should be clearly stated.
There is no conflict of interest. We never profit from our recommendations.
As a background, although we charge a fee for undertaking damp surveys, profit is not our primary motivator. We are motivated to:
- solve damp problems in properties,
- encourage clients to spend money wisely for the protection of the property and, where possible to lower the environmental impact,
- stop or at least play our part to reduce the over-diagnosis of rising damp and so called “damp proofing” treatment by replacing plaster with chemicals and slurry, rather than dealing with the root cause.
| Questions and Answers |
|---|
Relevant examples of similar damp issues or remediation:
To Be Completed.
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Ask A.I. about your report, in the “Type your message” you could ask:
What does the damp report say are the main causes of damp and main actions to stop damp?
¿Qué dice el informe de humedad sobre las principales causas de la humedad y las principales acciones para detenerla?
潮湿报告说什么是潮湿的主要原因和防止潮湿的主要措施？
नमी की रिपोर्ट के अनुसार नमी के मुख्य कारण और नमी को रोकने के लिए मुख्य कार्य क्या हैं?
Que dit le rapport sur l’humidité concernant les principales causes de l’humidité et les principales actions pour l’arrêter?
Was sagt der Feuchtigkeitsbericht über die Hauptursachen von Feuchtigkeit und die Hauptmaßnahmen zur Bekämpfung von Feuchtigkeit?
Что говорится в отчете о влажности о основных причинах влажности и основных действиях по ее устранению?
Cosa dice il rapporto sull’umidità riguardo le principali cause dell’umidità e le principali azioni per fermarla?