Condensation – the bigger picture


Condensation– the bigger picture

The start of spring seems like as good time as any to reflect on another condensation season, but rather than concentrating on the causes and ‘cures’, I would like to discuss some of the issues that make the elimination of condensation extremely challenging for many households.

Condensation is described as the leading cause of dampness in the UK, and can obviously affect any property no matter its age, market value and construction type. Increasingly, it is our experience that the occupants who appear to suffer the most (and for the longest period) from condensation problems, are those private tenants who live in older properties at the more affordable end of the rental market.

This article looks at condensation dampness and introduces some of the socioeconomic driving forces that can make controlling condensation and its associated black mould, very challenging for many private tenants.

What is condensation ?

OK, for context, we best briefly cover the causes of condensation, so here goes;

Condensation is the process by which water vapour in the air is changed into liquid water.
Simplify put, warm air can hold more water than cold air, having a greater holding capacity the warmer the air becomes. The ratio of water vapour the air can hold at any given temperature is defined as relative humidity (%rh).
If that moisture-laden warm air is cooled to such an extent that it can no longer hold the vapour (100%rh), then it will change to a liquid phase as condensation. The temperature that 100% relative humidity occurs, and therefore condensation, is known as the Dew Point temperature.

Mould is often associated with prolonged periods of condensation dampness, and can become a health issue in the worst affected properties, increasing the likelihood of suffering respiratory problems, asthma and allergies. This becomes more significant when we consider that the Energy Saving Trust suggests that a third of UK homes suffer mould issues, that’s approximately 8 million properties, potentially affecting 20 million people.

Condensation ‘Lifestyle’ Phenomena

Condensation is usually referred to as a ‘lifestyle’ phenomena, the consequence of moisture generation from the activities of occupants, exacerbated by ventilation, heating and thermal inadequacies.

Typically, condensation forms on the inside of windows, particularly common on single-glazed windows, door and window reveals, and the corners of rooms.

Interstitial Condensation

Often overlooked, condensation can also form within materials, known as interstitial condensation, which can lead to serious mould and rot formation that often goes unnoticed until materials begin to fail.

How to prevent condensation

Improved ventilation, that is increased air changes, have become the default recommendation to managing condensation problems, with maintaining a well controlled heating regime and improving insulation also part of the well established remedial guidance (Shelter provide some easy to understand guidance).
So now that we know its causes and cures, why are so many people still living with these problems when it is said to be easy to cure?

There is an intriguing narrative to why condensation dampness has become a real public health issue in the 21st century, so let’s take an albeit brief, but closer look.


We live in a time of massive change which have consequences for the UK’s built environment.
Socioeconomic conditions and reactions to climate change are just two of the driving forces that have influenced how we now build, occupy and interact within our built environment.

Construction has ‘evolved’ from relatively draughty buildings to more energy efficient, airtight and super-insulated properties that make passive control of moisture a thing of the past.

As well as draughty doors and windows, traditionally constructed buildings (pre-1919), usually had one or more open fires that would also help manage indoor humidity. They were also constructed with vapour open materials such as, masonry, lime plaster and timber, which would readily absorb and release moisture as environmental conditions changed.

Today, the onus is on energy efficiency with new build properties focussing on insulation and airtightness. Many of these properties have multiple bathrooms, tumble dryers etc, generating more moisture, and we are becoming increasingly reliant on technology to manage this moisture and the indoor air quality. This is further exacerbated by our sedentary lifestyles, with many adults and children spending more time indoors than previous generations. Unfortunately, moisture isn’t controlled adequately in many properties and it is these that are susceptible to condensation dampness.

Economic Pressures

It is estimated that 2.5 million households in England live in fuel poverty, where their income would fall below the official poverty line if they spent the actual amount needed to heat their homes, with those living in privately rented properties said to be worst affected (

Housing Shortage

Population growth, an increase in life expectancy, and a rise in one-person households have put considerable pressure on the housing supply. Those pressures combined with property speculation, house price inflation and stagnant wages illustrate why demand for affordable property outstrips supply: so much so that home ownership is fast becoming unobtainable for many young people, with an estimated third of the whole population now living in rental accommodation.

Private Rental

While social housing represents some of the best quality properties we inspect, as reported, it is those living in the most affordable private sector properties that are most likely to experience problems associated with condensation dampness.
Most of our condensation-related damp assessments are undertaken on these private rental properties, where tenants are often placed there by local authorities due to a shortage of social housing.

Hard to Heat 

Many of these properties are termed ‘hard to heat’, meaning they are poorly insulated and lose/waste energy, which equates to higher fuel bills.  Note,  damp walls lose considerably more heat than dry walls (approx. 40% more!).

There are an estimated 267,000 private rental properties in England that are caught within the most inefficient F and G energy bands, with 122,000 of those tenants suffering the worst extremes of fuel poverty, some having to pay over £1,000 more for energy than households not living in poverty.

Although a reduction in moisture production and improved ventilation are the main tools to manage condensation, controllable heating will help to raise the surface temperature and minimise cold areas (and heat loss!). But much of the housing stock we inspect are traditionally constructed properties, and although many make great homes, inherent thermal limitations, often compounded by inappropriate refurbishments and ill conceived ‘improvements’, means that there is no shortage of reports of condensation damp related problems.

We regularly see black mould affecting door and window reveals with the coldest sections of walls and ceilings covered in mould in the most severe cases. Quiet often, we are met with a familiar musty odour as soon as we are invited into to the property, which is symptomatic of a significant mould problem.


Although most of our condensation-related work supports frustrated tenants who are concerned about the potential health issues associated with living with significant condensation dampness, we do assist proactive letting agents and landlords from time to time: whoever the client may be, we believe it fundamental that those involved in disputes remain totally objective and simply present the facts which will hopefully help draw the tenant and landlord together with a common goal of improving living conditions and better managing dampness.


I would conclude in saying that although in the vast majority of properties we investigate, yes it is the occupant who has been responsible for generating high levels of humidity, however, we also find that it is inadequacies associated with the building fabric and its services that have facilitated the formation of condensation and mould.

We would hope that those tasked with providing solutions to condensation and other moisture-related building issues take an holistic approach to controlling these damp problems.
We would also advocate the use of more appropriate materials in retrofit and improvement schemes, promoting the use of hygrothermally responsive materials (maybe another article?), rather than continuing the recent trend of utilising insulations and finishes that prove unsympathetic and often detrimental to how older buildings ‘work’ – great refurbishments needn’t be cost prohibitive!