Background
Owned and inhabited by the residents, the semi-detached dwelling shares a party wall with the property on the left, managed by a housing association. The dwelling extends approximately 60 cm beyond its neighbour’s frontage. Dampness has been identified within this protruding section of the internal wall, facing the left-hand neighbour’s front garden. Symptoms of damp—mould, white salts, and brown stains—first appeared in March 2024 on the lower part of the ground floor wall. The accumulation of bags and discarded furniture, often wet from rain and in contact with the wall in the neighbour’s garden, was noted. Upon request, these items were removed by the house manager, a process repeated in May. Despite removals, damp symptoms worsened post-summer, ascending the wall to the first-floor bedroom directly above the initial affected area. By November, exacerbation of dampness was observed following the neighbour’s use of a water pressure hose on the exterior. Although reported to the adjacent property’s maintenance, with gutter clearance suggested as a remedy, the effectiveness of this intervention remains uncertain. Currently, the damp affects both ground and first floors, extending from the bottom to the top of the ground floor wall, and halfway up the wall on the first floor.
Data loggers
In conclusion, from data gathered from the loggers
- We know from the colour and shape of the damp that it is caused by rainwater penetrating through. However, you also have some high humidity caused by insufficient ventilation. Excess vapour had been the primary or sole cause of damp, then we would see dampness and mould in other more vulnerable areas, such as the front corners of the bay and corner of the detached side of the house.
- High vapour levels, (dew point relative to temperature) will slow down the drying process. Using targeted ventilation, a good dehumidifier and a fan directed onto the wall, perhaps with some heat, will speed up the drying process.
Evidence & Illustrations
To keep the property dry | |
|---|---|
| Ask neighbour to repair gutters. | |
| Ask neighbour to inspect the gutters and downpipe and adjust and or fix the leak. This should be followed by a test during a rainstorm or with large vessel of water to make sure the gutter or downpipe leak is correctly repaired. | £180 |
| Ask neighbour repair render cracks | |
| The neighbour should fill all render cracks, this should include cracks on the left side of their property, and between the two properties. 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. | |
| 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 |
| Use fan to expedite drying | |
| Direct a fan onto the damp patch to speed up the drying process. | |
| 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. | |
| Target vapour from cooking with an extractor fan | |
| Always use the kitchen extractor fan when ever cooking, and cook with tops on pots and pans. | |
| 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. | |
| 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. Keep internal dew points below the external temperature by increasing the targeted of vapour, as above, and using a good dehumidifier, 24/7, including when away, until dew points start to align with external temperatures. | |
| 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. | £23 |
| Keep objects away from walls | |
| Consider moving objects away from damp walls. | |
| Remedial actions – estimate of costs | £383 |
Actions if all else fails | |
|---|---|
| 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 |
| Optimal actions – estimate of costs | £100 |
I conclude that damp originates from rainwater pouring down the neighbour’s side, entering through cracks in the render.
Moss and algal growth from rainwater pouring onto the neighbour’s side, defects in the neighbour’s render, signs of water on their side all demonstrate that the damp originate from their side.
Assisted with 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 £0,050. 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 240108SH1200. I conclude that damp originates from rainwater pouring down the neighbour’s side, entering through cracks in the render. 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 240108SH1200
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: Owners concerned about potential rising damp due to water appearing at the base of the wall
- Damp treatment: Standard DPC, no signs of past damp proofing treatment
- Weather: To be checked
- Property: Edwardian or mid-war terraced house
- Background: Property bought in 2020 with no issues related to this wall flagged on the survey
- Changes: Rendering added to front and rear walls, damage to rear wall; neighbour’s property of different period with cracked render
- Occupancy: Family
- Mould & notes: Mould present behind television and a toy in the bedroom above
- Primary damp concern: Front wall
- Other damp concerns: None mentioned
- Compounding: Heat loss from the wall being exterior
- Airbricks: No concerns
- Sub-floor humidity: Not a concern
- Tenure: House
- Attachment: Attached on the right-hand side but set back
- Build: Edwardian or post-mid-war
- Walls: 9-inch thick solid walls
- Exterior comment: Green streak of moss or growth on the neighbour’s side next to the wall
- Penetrating damp assessment: Penetrating damp observed
- Drains: Functioning correctly
- Leak signs: No signs of leaks
- Leak assessment: Leak unlikely
- Floor: Not a concern
- Loft: Not a concern
- Timber assessment: Timber does not appear damaged by leak water
- Last dry: Property was dry upon purchase in 2020
- Ventilation assessment: Kitchen vent fails to remove vapour effectively; bathroom vent underperforming
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.
