Condensation: a real and present danger, not a damp squib

Condensation forms when the humidity level in the indoor air reaches saturation point and that air comes into contact with a cold surface, turning into liquid water. These cold surfaces are most commonly windows, but can also include ceilings, walls, window-sills and the corners of a room that have an external wall, writes Paul Williams, Domus Ventilation Product Manager.

Whilst condensation can form throughout the year, it’s the winter months that present the greatest challenge. As temperatures drop, residents turn their heating systems on and naturally close windows to prevent that heat from escaping. This also prevents the moisture from escaping, increasing humidity levels and the risk of condensation. The colder the surface, the more likely condensation is to form, especially during the night when the heating goes off, the temperature drops and the air can no longer contain the moisture and finds all the cold spots to condense.

Surface condensation is caused by the high humidity linked to everyday home activities such as cooking, bathing, washing and drying clothes, and even just breathing. Kitchens and bathrooms are usually the most affected areas as moisture levels are typically highest, but condensation can occur in other areas as well, especially colder rooms.

Condensation isn’t just a nuisance. Excess condensation left within a property can lead to the formation of damp patches then mould growth, resulting in potential health impacts.

Condensation also has consequences for the property. Mould and dampness can lead to musty smells, staining, peeling wallpaper, cracked wall surfaces, plaster degradation, warped window frames and even structural damage over time, all of which comes at a cost to repair.

The English Housing Survey Headline Report 2020-21 stated that in 2020* 2% of homes had problems with condensation and mould. When you consider there are an estimated 24 million households in England, that 2% equates to 480,000 homes suffering from serious condensation and mould.

The problem is most prevalent in private rented dwellings where 6% had some type of damp problem, followed by 4% of social rented dwellings and 2% of owner-occupied dwellings.

The good news is that all damp related problems in housing have been on a downward trajectory from the 1960s. The bad news is that condensation and mould reduction has stalled, with only a slight reduction in figures over the past decade.

So, what can we do to reduce condensation in our homes?

Over the years, the onus has been very much placed on residents to make lifestyle changes. These have included drying clothes outside when possible or using a tumble dryer, covering pans when cooking, shutting the bathroom door when showering or bathing, and ensuring extraction fans are switched on.

However, for many low income households that are struggling to adequately heat their homes, and therefore have a higher level of condensation, these measures are not always economically viable. Furthermore, recent research has verified that construction and external factors play more of a role in the development of these issues than residents’ behaviour – damp and mould are directly linked to badly insulated and poorly ventilated houses.

So, it’s time to stop laying the blame at the door of the resident and start making our homes more condensation proof.

If we improve the ventilation in a home, we lower the humidity. Circulating the air and extracting excess humid air outdoors can be accomplished through a number of different ventilation solutions, depending on the budget available, the nature of the property and the seriousness of the issue.

For existing properties, the most cost-effective options are bathroom and kitchen intermittent extraction fans or single flow, continuous running decentralised mechanical ventilation fans. Positive Input Ventilation (PIV) units can also be used, which gently pressurise a dwelling to expel stale and humid air through natural ventilation points.

For new builds, the options are more widespread and ultimately more effective. In addition to intermittently operating extraction fans, Mechanical Extract Ventilation (MEV) units and Mechanical Ventilation with Heat Recovery (MVHR) can be deployed.

MEV units provide constant low level ventilation by extracting waste, damp air from a dwelling through a system of ducting. These are best suited to apartments and small to medium sized houses.

MVHR systems go one step further by combining extraction with supply. The extracted air is passed across a high efficiency heat exchanger located inside the MVHR unit, to remove and transfer the otherwise wasted heat. The exhaust air is then expelled into the atmosphere. At the same time, fresh filtered supply air is drawn across the opposite side of the heat exchanger and pre-warmed before being distributed through ceiling mounted grilles to habitable rooms.

The new MVHR units on the market are highly energy efficient, with models available with integral humidity sensors. By accurately measuring air humidity, the extract speed automatically changes from background to boost as the level of humidity increases, thereby providing optimal ventilation performance.

These mechanical systems provide a long term and cost-effective solution rather than short term problem ‘hiders’ such as dehumidifiers.

The issue of condensation in our homes remains and is not improving fast enough. Expecting people to change their lifestyle to prevent excess condensation is not realistic, nor will it reduce condensation to comfortable levels. Building adequate ventilation into our homes is by far the more realistic and long-term solution.