Condensation In The Home: The Basic Principles

The Winter months are well and truly upon us, and so too are reports of condensation related issues and mould growth. With this in mind, we thought it would be an ideal time to write a blog outlining the basic principles of condensation, the effects it can have, and how to go about alleviating condensation in the home.

So what is condensation?

Water essentially has three different states: solid (ice), liquid (water), and gas (vapour). All air contains a certain amount of water which floats around in its gas state. This is known as water vapour. The air within your home is no different and will therefore contain a certain amount of water, which is completely normal.

The quantity of water within the air is referred to as humidity. Air can only hold on to a certain amount of water before it becomes saturated. The amount of water the air can hold on to is determined by the temperature of the air. The warmer the air is, the greater its capacity is to hold water. The colder the air is, the lower its capacity is to hold water.

The air’s ability to hold water in relation to its temperature is known as relative humidity, and this is usually expressed as %RH. Relative humidity is defined as the amount of water vapour contained within a given volume of air compared with the maximum amount of water that could be in the same body of air, at the given temperature.

When air reaches 100% relative humidity it becomes saturated and does not have the ability to hold on to any more water. This is known as the dew point. When the air drops to, or below the dew point, condensation occurs because the water condenses from water vapour to liquid water.

As an example, if moist air comes into contact with a colder surface such as a single glazed window, the air is cooled; if the air is cooled to or below the dew point temperature, the water vapour will condense to liquid water on the window.

What impact can condensation have?

The issues associated with condensation can vary from minor damage to finishes such as wallpaper, to serious structural issues.

Damage to Finishes

This can include water staining marks on walls, ceilings, and other surfaces. It can lead to staining/peeling of paint and bubbling/spoiling of wallpaper which can be unsightly and costly to redecorate.

Damage to Structure

If condensation related issues are allowed to continue for a prolonged period without intervention, this can lead to significant structural issues. Water can start to saturate roofs, ceilings, walls, and floors, causing deterioration and decay to timber elements. This can eventually lead to complete failure of building elements and require costly and disruptive repair works.

Mould Growth

One of the most common issues relating to condensation and more specifically, high levels of humidity, is the formation of mould and mildew. If humidity levels remain above 70% for long periods, there is a very high risk of mould growth forming. Not only is mould unsightly and damaging to finishes, but it can also pose significant health risks especially to anyone with respiratory issues or allergies. The presence of black spot mould is normally a good indicator the dampness is condensation rather than penetrating or rising damp.

How to control levels of condensation?

It’s important to understand that we add moisture to the air in our home all the time, just by doing essential everyday things such as breathing, cooking, showering and drying clothes etc. In fact, the average family can create up to 20 litres of water per day, just by doing normal everyday activities.

It may come as a surprise to some, but air containing anywhere between 40%-60% of its holding capacity is ideal. If the air is lower than 40%RH, it can become unpleasant for occupants and cause issues such as dry skin and irritated eyes. Conversely, if the air is higher than 60%RH, it is too humid and can be uncomfortable for occupants, whilst also increasing the risk of condensation related issues and mould growth.

It’s therefore not possible, or indeed healthy, to eliminate moisture in the air, but it’s important that humidity levels are controlled. In order to do this, the correct balance of heating, ventilation, and insulation must be achieved as outlined below.

Heating

Example of low internal air temperature and high humidity levels.

It’s essential to ensure the property is adequately heated, especially during Winter months. The temperature should be consistent throughout the property even when unoccupied, with large fluctuations in temperature avoided if possible. Ideally, the temperature should remain between 18-21 degrees celsius at all times (remember, warmer air has a greater capacity to hold on to water in comparison to colder air).

The vast majority of homes are heated via a central heating system, which is controlled by a timer or thermostat. The timer and/or thermostats should be set accordingly to ensure a consistent and balanced heating cycle. ‘Smart’ thermostats are also now widely available and can be relatively straightforward to install, making temperature control even easier. In addition, regularly servicing the boiler and ensuring all radiators are working correctly will help ensure the heating system is operating efficiently.

Example of a basic hygrometer which can be purchased online.

A good way to keep track of internal air temperature and humidity levels is to purchase some basic hygrometers and place them in different rooms throughout the property. These can be bought online for only a few pounds each.

Ventilation

Adequate ventilation is a key factor in alleviating condensation and maintaining a healthy and comfortable living environment. Ventilation helps expel moisture laden air which in turn reduces the levels of humidity. The type of ventilation strategy depends on a number of factors including the construction type and occupancy of the building however, it often includes a combination of natural and mechanical ventilation systems.

Here’s are a few ways which can improve ventilation within a typical home:

• Trickle vents – Installing and operating trickle vents on windows will improve continuous background ventilation and help maintain good air-circulation.

• Undercut to doors – Ensure all internal doors have a minimum 10mm undercut (gap) between the bottom of the door and floor finish. This will help air circulate between rooms, allowing for a more balanced airflow throughout the property.

• Furniture – Furniture should be kept clear from external walls if possible. If this is not possible, ensure there is a gap between the furniture and external walls to allow air circulation behind.

• Mechanical Extraction – Installing and operating mains mechanical extraction (such as extract fans and cooker hoods etc.) in ‘wet rooms’ such as kitchens, utility rooms, and bathrooms is essential to help remove moisture generated from the source. It’s important these are regularly cleaned and maintained to ensure they are working efficiently.

Example of furniture placed tight up against external wall restricting air circulation behind.

Additionally, being mindful of the amount of moisture generated in the home through everyday activities, and limiting this were possible, will also help reduce humidity levels. This includes; putting lids on pots and pans when cooking, closing the bathroom door when showering, avoiding drying clothes indoors, ensuring non-condensing tumble driers are properly vented externally etc. Implementing minor lifestyle changes such as these can significantly reduce the changes of condensation occurring and, as there are no cost implications, these areas should be considered first.

Insulation

Example of thermal bridge to ceiling as a result of missing loft insulation directly above.

Insulation is another essential factor in helping to manage levels of condensation. A well-insulated building helps keep heat in for longer. This helps maintain a stable internal air temperature whilst also reducing heating bills. Additionally, a properly insulated building helps regulate surface temperatures such as walls and ceilings, keeping them above the dew point temperature and thereby reducing the risk of condensation.

Example of missing section of loft insulation causing a thermal bridge to the ceiling below.

It’s important to highlight that insulation must be properly considered and installed, especially retro-fit insulation to existing buildings. The insulation material must be consistent throughout with no openings or gaps. Poorly installed insulation can create thermal bridges (cold spots), reducing the surface temperature of the area in question and increasing the risk of condensation and potentially black spot mould.

It’s also worth noting that no matter how well insulated a building is, if its poorly heated, surface temperatures can still drop to or below the dew point. Insulation on its own will be of little benefit in combatting condensation unless adequate heating is provided.

Summary

Understanding the basic principles of condensation and maintaining the correct balance of heating, ventilation, and insulation are crucial in order to successfully manage the levels of condensation in the home.

If you are concerned about condensation within your home and not sure where to start or how to manage, feel free to reach out to us to learn more about how we can help.