In conclusion, from the data loggers
Overall the dampness in the kitchen is not caused by condensation, penetrating damp from the loft, the data supports the visible signs of hygroscopic salts, see later. There is high humidity in the bathroom, which I will have helped by improving the ventilation, see other recommendations.
Various issues were observed in different areas of a 1900s maisonette with a loft conversion. In the kitchen, a rotten patch in the window frame was noted, along with some mould that was subsequently treated. The bathroom exhibited peeling paint and mould around the window frames, which also received treatment. The back staircase leading to the garden emanated a damp smell following rainfall. In the unboarded loft space, concerns about the dampness of the chimney breast were raised, following repairs to a cracked chimney and capping of chimney pots approximately 4-5 years ago, though it remains uncertain if these measures fully resolved the issue. Additionally, a damp smell was detected from the loft conversion, extending into the first floor hall after rain.
Evidence & Illustrations
To keep the property dry
|Hygroscopic salts act like grease stains. They are benign, cause no damage or mould, but are unsightly, especially in summer during a heat wave, and cause problems renting or selling a property (keep this report to show prospective buyers). The best solution is to cover the salts, with an impermeable blocking material, with a significant overlap of at least 300mm (to reduce the risk of enlarging the damp patch). Ideally treat each section of wall equally, so that it is homogenous and therefore absorbed or repels humidity in the same way. Hygroscopic salts can be just under the surface. The simplest, cheapest and in my opinion the best is using 2 coats of Zinsser B.I.N. Cover Stain, a solvent-based, primer-sealer. For each patch, it takes about 1 hour and costs around £15 plus any labour if required, the great thing with Zinsser is it is easy strip off and reapply. For significant areas consider painting a coat of gloss paint sandwiched between two layers of Zinsser BIN Cover Stain, and ideally paint all sections of wall affected, as like icebergs, there can be more hidden just below the surface. Most homeowner would attempt this. It will take a general builder a few hours, and so should be considered as part of a larger project. For saturated walls and if it doesn’t work immediately, consider sandwiching a layer of an oil base paint between two layers of Zinsser oil based primer, then you can complete with a standard emulsion. Try an out of sight area first.
|Paint mist coat
|Paint mist coat to ensure adhesion to the unpainted plaster in the bathroom and wall by the staircase to the garden.
|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.
|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 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).
|Treat window rot
|For the timber affected by window rot, sand, fill, and paint with an appropriate protective product.
|Remedial actions – estimate of costs
Actions if all else fails
|Duct out kitchen extractor fan
|Consider instructing general builder to duct out kitchen extractor fan (hole required to duct outside, which may require freeholder permission).
|Consider insulating the stair case walls. It is better to use vapour active insulation, such as thermal insulating lining paper, such as Wallrock.
|Optimal actions – estimate of costs
I conclude that there was the damp patch is caused by hygroscopic salts from the historic burning of coal and condensation from a defective bathroom fan, and well as drying clothes indoor and lack of effective kitchen extractor.
calcium nitrate a hygroscopic salt, causes a form of condensation called deliquescence at normal levels of humidity of 50%RH. They are often found in Victorian chimneys from burning coal. They appeared to have been released when the chimney breast was replastered.
I repaired the defective bathroom fan. By taking a root cause approach, rather than a focus on blocking the symptoms of damp the savings are likely to be around £2,000. 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 231117SH0800. I conclude that there was the damp patch is caused by hygroscopic salts from the historic burning of coal and condensation from a defective bathroom fan, and well as drying clothes indoor and lack of effective kitchen extractor. 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.
Site visit 231117SH0800
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.
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: You were concerned about damp.
- Weather: light drizzle during survey
- Property: Victorian ground floor flat
- Background: roofing repairs have not solved damp.
- Changes: conversion into flats, central heating, double glazing with no or insufficient trickle vents and lifestyle changes including more frequent showers and clothes washing, including greater occupancy during the Covid pandemic.
- Occupancy: couple
- Mould & notes: mould smell
- Primary damp concern: dampness on chimney breast
- Other damp concerns: mould
- Compounding: defective ventilation
- Airbricks: There is no reason to be concerned about the sub-floor ventilation.
- Sub-floor humidity: There were no concerns about humidity in the sub-floor void.
- Tenure: top floor maisonette
- Attachment: a terraced
- Build: Victorian
- Walls: solid wall made of two brick widths (225mm)
- Exterior comment: There were 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 floor is of no special concern.
- Loft: The main loft has been converted. The food void above the kitchen is dry.
- Timber assessment: There are no suspicions of significant timber decay, other than around a window frame, which is not structural per se and caused by condensation.
- Last dry: Damp issue started showing a few years ago.
- Ventilation assessment: The bathroom vent is defective, I repaired it. The kitchen vent is not ducted out.
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.