Relative humidity (RH) plays a crucial role in condensation, which occurs when water vapour in the air cools and changes from gas to liquid form. This is called the Dew Point.
Understanding Relative Humidity
Relative humidity is an accurate measure of the amount of water vapour in the air compared to the maximum amount that the air can hold at a given temperature.
It is expressed as a percentage.
For example, a Relative Humidity of 50% means the air holds half of the water vapour it could at that temperature before being completely saturated. Therefore, temperature has a direct effect on Relative Humidity.
It is not a measure of how much water is in a room and should not be used in isolation to infer water leaks.
The Condensation Process
- Saturation Point: When the air reaches 100% RH, it is considered to be saturated. At this point, the air can no longer hold additional moisture, and any further cooling will lead to condensation.
- Cooling Air: As air cools (for example, during the night or when it comes into contact with a cold surface), its capacity to hold onto moisture decreases. If the temperature drops enough for the RH to reach 100%, the excess water vapour begins to condense into liquid water. This temperature is called the Dew Point.
- Dew Point: The Dew Point is the temperature at which air becomes completely saturated. When air cools to its dew point, condensation occurs. A higher RH means the dew point is closer to the current air temperature, increasing the likelihood of condensation. Again, this is not a measure of the moisture content of a wall, ceiling or floor.
Factors Influencing Condensation
- Temperature Changes: Rapid cooling of surfaces or air can lead to condensation, particularly in environments with an already high RH.
- Air Movement: Areas with stagnant air can experience higher RH, leading to increased condensation on surfaces.
- Surface Temperature: Cold surfaces (like windows or walls) can cause the air in contact with them to cool rapidly, triggering condensation if RH is high.
Implications
- Building Materials: In buildings, high RH can lead to condensation on surfaces, promoting mould growth and damage to materials
- Comfort Levels: High indoor RH can lead to discomfort and health issues, making it important to manage humidity levels effectively.
Protect Your Property from Condensation Risks
In summary, relative humidity is a critical factor in the condensation process. Higher RH increases the likelihood of condensation occurring, particularly when the air cools to its dew point. Managing humidity levels is essential in both indoor and outdoor environments to prevent the adverse effects of condensation.
The Energy Saving Trust recommends heating a dwelling to between 18°C to 21°C during winter.
The World Health Organisation (WHO) suggests 18°C is the ideal temperature for healthy and well-dressed people during normal occupation.
Temperature, lack of ventilation and an increase in air pressure can all have a detrimental effect on Relative Humidity.
Heating provisions (such as radiators, wall-mounted electric heaters etc) should be regularly used to keep the air temperature consistent.
Occupants of a property should also take steps to ensure that the property is adequately heated and ventilated, particularly during the colder seasons, and make positive changes to keep the relative humidity within the range of 40% – 60% and room temperatures around 18°C for the bedrooms and 21°C for the living room.
We are currently working alongside a number of Social Housing Providers in an Expert Witness capacity providing Part 35 Compliant Reports in response to Housing Disrepair Claims, many of which can be easily addressed through proper control of Relative Humidity.
Get in touch here to see how we can work together.