In 1982, in this magazine, David Ormandy wrote an article, ‘Condensation’, for lawyers and others involved in legal actions relating to condensation and mould, to ‘counter the suggestion often made … that increasing the heat and opening the windows is all that is necessary’ to solve the problems. Unfortunately, that ‘lifestyle’ defence is still rife 41 years later so what follows is an updated analysis of this persistent housing problem.
Dwellings should be designed, built and maintained for occupation by a spectrum of potential households – from those with young children to the elderly, and everyone in between. If a dwelling cannot cope with the moisture generated by day-to-day biological and domestic activities without condensation and mould, then the dwelling is at fault. Dwellings affected by condensation and mould are a threat to health, and can kill.
Condensation is one form of dampness.
1Condensation and dampness. BRE Expert Collection 7, Building Research Establishment, 2016. Others include: rising damp affecting walls and floors in direct contact with the ground; penetrating damp from rain entering through holes and gaps in the structure; and traumatic damp from a burst pipe or tank. These are obviously caused by structural defects, and so is condensation, but the cause isn’t so obviously related to the structure so, if the dwelling is occupied, the occupiers get blamed.
There are two main areas where occupiers are wrongly blamed for condensation and mould – lifestyle and ventilation: it is alleged that their lifestyle generates excessive moisture; and that they are not ventilating properly or at all.
What is condensation?
Moisture (as water vapour, a gas) is always present in the air, and the amount a given volume of air can hold depends on the temperature – the higher the air temperature, the more water vapour it can hold. The ratio between the amount of moisture held by a volume of air compared to the maximum it could hold at that temperature is the ‘relative humidity’ (RH) – for example, 60% RH at 20oC.
Ideally, the RH within a dwelling should be between 30% and 70%; any lower and it will start to feel uncomfortable (dry), and any higher and it will start to cause damp problems. However, within a room (and a dwelling) there will be air temperature gradients, both horizontally and vertically – higher close to heat sources and lower next to cold(er) surfaces. This means that the RH differs from point to point, although the amount of water vapour will not vary.
If the RH persistently exceeds 70% then ‘damp’ problems occur. Visible dampness – condensation – occurs when the air becomes saturated (ie, the RH exceeds 100% – the ‘dew-point’) and any excess moisture is given up. This condensation occurs on cold(er) surfaces that have reduced the air temperature, such as window glazing and cold(er) areas of walls where heat passes through to the outside.
Moisture produced in a dwelling
A household will naturally produce moisture through domestic and biological functions and activities. A realistic estimate of the moisture generated by a four-person household over 24 hours is between 5.0 and 10.0 litres, broken down as follows:
•1.0–2.0 litres by four persons asleep for eight hours;
•1.5–3.0 litres by two persons active for 16 hours; and
•2.5–5.0 litres by cooking, bathing/showering, dishwashing etc.
There will also be irregular (perhaps weekly) sources like laundry and hand-washing clothes (5.0–10.0 litres) and drying clothes indoors during bad weather (3.0–7.5 litres).
The amount generated will depend on the size and composition of the household and the amount of time spent in the dwelling. An elderly household could spend more time indoors than a working couple; and a household including infants will probably spend more time indoors, and carry out more personal and clothes washing. Variations between different households are surprisingly small; even a single-person household will generate around 4.5 to 10.0 litres over 24 hours, plus an irregular 5.0 to 8.0 litres.
Dwellings should be of a size and layout to suit potential households, and, as occupation will change over the years, they should be capable of being occupied by a spectrum of households without any condensation problems. If a dwelling is not designed, constructed or maintained to be capable of avoiding condensation problems then there is something wrong with that dwelling. Occupiers should not be expected to compensate for, or suffer the consequences of, those failings.
Ventilation
Occupiers are blamed for condensation and mould because they haven’t properly ventilated, they haven’t opened windows – but do their accusers know what ‘proper ventilation’ is?
Ventilation is necessary to replenish the internal air, provide air for fuel combustion and remove excess moisture. Dwellings should be provided with effective, controllable means of ventilation that take account of the location, the internal layout/design, the facilities/appliances and the room/space use.
2Improving ventilation in housing: Good Repair Guide 21, Building Research Establishment,1998 (note this is now a little out of date). See also: Existing home ventilation guide, Department for Levelling Up, Housing and Communities, December 2021.The air in a room/dwelling should be replaced about once every two hours; air changes above this for general parts of the dwelling will increase the heat loss. Windows need not, and should not, be opened wide; opening a small amount will provide adequate trickle ventilation (modern double-glazed units incorporate trickle vents). For periods of high moisture production in kitchens and bathrooms (such as cooking and showering) there needs to be increased localised extraction to prevent moisture drifting to other parts of the dwelling.
For dwellings in an exposed location (eg, an exposed hillside or high in a tower block) the ventilation needs and provision must be different from one in a sheltered position, but both will need controllable ventilation built in and maintained. Where a dwelling is adjacent to noise sources (eg, busy roads or railways), or at ground level next to a thoroughfare, then noise and security concerns will deter opening windows that can’t be secured. Again, safe, controllable ventilation needs to be built in and maintained.
Ideally, there should be through-ventilation (front-to-back or side-to-side) so rooms and other areas can exchange air and maintain a balanced atmosphere. For single aspect dwellings (all rooms facing one direction as in some blocks of apartments) there should be built-in (quiet) mechanical means of ventilation.
3A main reason why ‘back-to-back’ houses were deemed unfit under the Housing Act 1957 was the inability to achieve through-ventilation.The provision and maintenance of the ventilation facilities should take account of the dwelling design and appliances. Solid fuel stoves or open fires require air to burn and to take away combustion products; similarly for gas fires and gas water heaters, which need air for combustion and for the removal of gases given off when burnt (these gases include water vapour).
Cooking generates moisture and gas cookers create more moisture as well as other (poisonous) gases. During cooking (and other periods of high moisture generation), there should be effective means of safely removing excess moisture to the outside. Mechanical extractor fans are the most effective, preferably fitted with humidity-sensitive switches (rather than relying on manual control). Clothes washing (laundry) is often carried out in the kitchen area and, while modern washing machines put out little additional moisture, hand-washing clothes may add to that from cooking.
Personal washing, particularly using showers, can generate high levels of moisture. Again, there should be effective means, such as built-in mechanical extractor fans, to safely remove excess moisture to the outside.
Clothes drying is a potential source of moisture. Drying laundry outside avoids potential condensation problems, but it depends on the weather, security and the type of dwelling. Drying outside needs space, which is not always available for dwellings in purpose-built and converted blocks. Built-in clothes-drying cabinets (with low-level heating and vented to the outside) or purpose vents for tumble dryers will avoid moisture problems.
Energy efficiency
Relevant to the likelihood of condensation is the energy efficiency of the dwelling.
4‘Efficient’ is defined by Chambers Dictionary online as ‘producing satisfactory results with an economy of effort and a minimum of waste’. This should be such that the potential range of occupiers can afford sufficient energy to heat the dwelling to avoid thermal discomfort and threats to health from exposure to low indoor temperatures,
5Hayley Janssen et al, Cold homes and their association with health and well-being: a systematic literature review, Public Health Wales NHS Trust, November 2022. as well as avoiding threats of condensation.
Energy efficiency depends on the thermal insulation of the structure, the effectiveness of the heating system and the use made of it. The insulation and heating system are the responsibility of the owner. The use made of the heating system depends on the effectiveness of the thermal insulation, the effectiveness of the heating system and whether using that system is affordable. Inadequate thermal insulation wastes heat (adding to climate change problems) and money, and an ineffective heating system will not provide sufficient heat throughout the dwelling.
As noted above, the higher the air temperature, the more moisture it can hold. If warm, moisture-laden air comes into contact with a cold(er) surface, such as an external wall, then condensation occurs. Whether a wall (or other part of the dwelling structure) is cold(er) depends on the energy efficiency of the dwelling. A dwelling fails if it has inadequate insulation and/or an expensive-to-use or ineffective heating system. Occupiers should not be expected to compensate for such failings.
Health threats from condensation and mould
Occupiers living with mould and condensation (and other forms of damp) are more likely to have symptoms such as eye, nose and throat irritations, coughing, wheezing and shortness of breath, and the worsening of asthma symptoms.
The likelihood and severity of the effects depends on the amount, extent and site of the mould and how long the occupiers are being exposed. Mould in a bedroom is more of a threat than in a bathroom; bathrooms are used (by everyone) for relatively short periods every day, but bedrooms will be used for at least eight hours in every 24. Those most susceptible to mould are infants, children, the elderly and those with existing health problems such as respiratory conditions or weakened immune systems,
6Damp indoor spaces and health, Institute of Medicine, 2004; WHO guidelines for indoor air quality: dampness and mould, World Health Organisation, 2009. and those who tend to spend more time within the dwelling.
As well as mould growth, high RH levels and condensation will significantly increase exposure to dust mite allergens.
7Ibid, WHO (2009). These microscopic mites are found in all dwellings, and the most successful protective action appears to be the reduction of dampness and high RH.
As well as the potential effects on physical health, the visual signs of mould affect mental and social health, making adult and young occupiers reluctant to invite friends into the dwelling. Adults will be affected by stress and anxiety, and adults and children will become isolated from friends and the community.
8Crowding (often referred to as overcrowding) can mean more moisture is generated than the dwelling was designed for, but this is a different problem with different solutions.The law
Housing Health and Safety Rating System and the Decent Homes Standard
Damp and mould is one of the 29 hazards in the Housing Health and Safety Rating System (HHSRS) – a threat to health caused by dwelling defects or deficiencies.
10Housing Health and Safety Rating System: operating guidance. Ministry of Housing, Communities and Local Government, 2006. Local authorities are under a duty to act to remedy the cause where a dwelling suffers from a category 1 hazard and have a power to act where a category 2 hazard exists.
11Housing Act 2004 Part 1; HHSRS category 1 and 2 hazards as defined by the Housing Health and Safety Rating System (England) Regulations 2005 SI No 3208 and the Housing Health and Safety Rating System (Wales) Regulations 2006 SI No 1702 (W 164). The duty and power apply in respect of all dwellings, whether tenanted/rented or owner-occupied, with the single exception of dwellings owned by the enforcing authority.
12R v Cardiff City Council ex p Cross (1982) 81 LGR 105, QBD; (1982) 6 HLR 6.The first criteria of the Decent Homes Standard (DHS) is that there should be no HHSRS category 1 hazard.
13A decent home: definition and guidance for implementation, Department for Communities and Local Government, 2006 (note that consideration is currently being given to extending this to all rented dwellings). Currently, the DHS is a non-statutory (administrative) standard applicable to social rented dwellings. However, as it refers to HHSRS category 1 hazards only, it could open a door to a challenge where there are (say) several category 2 hazards.
Fitness for human habitation
As well as the repairing obligations (Landlord and Tenant Act 1985 s11), the Homes (Fitness for Human Habitation) Act 2018 places an obligation on landlords to ensure the dwelling is fit throughout the tenancy. Fitness is to be interpreted by reference to 29 matters listed (these are the same matters as the 29 HHSRS hazards). Unfortunately, there is no cross-referencing to the HHSRS operating guidance (issued under Housing Act 2004 s9) and so no official guidance on interpretation of the matters relevant to fitness. (It may be useful to back up a claim of unfitness with a report from an environmental health officer.)
The author would like to thank Penny Wiles for comments and proof-reading of this article. He will be writing an article on fuel poverty v energy injustice in the April 2023 issue of Legal Action.