Understanding Condensation!

Condensation is the process where water vapor becomes liquid. It is the reverse action of evaporation, where liquid water becomes a vapor.

Air contains some water vapour; warm moist air holds more vapour than cooler air.

Condensation occurs in one of two ways:

  1. The air is cooled to its dew point.
  2. The air becomes so saturated with water vapor that it cannot hold any more water.

The dew point is the temperature at which condensation happens, Air temperatures can reach or fall below the dew point naturally, often at night which will make building elements cold either at or below dew point.

That’s why you see water droplets on the ground and around structures, and objects left outside in the morning.

You are likely to notice condensation on your window frames when you have a warm shower on a cold morning (cold aluminium at or lower than dew point temperature and warm moist air = condensation).

Condensation can also produce water droplets on the outside of a glass of cold water/beer. When warm air hits the cold surface, it reaches its dew point and condenses, leaving droplets of water on the glass.

Clouds are masses of water droplets in the atmosphere, as more water vapor collects in clouds, they can become saturated with water vapor.  As the density, or closeness, of the molecules increase the clouds cannot hold any more water vapor. The vapor condenses and becomes rain.

Cold air holds less water vapor than warm air. This is why warm climates are often more humid than cold ones: Water vapor stays in the air instead of condensing into rain. Cold climates are more likely to have rain, because water vapor condenses more easily there.

When looking at the weather conditions you will see a term Relative Humidity expressed as a percentage of the maximum amount of water vapor the air could hold at that temperature, the higher number more vapour in the air.

More Building related, we are worried about what is called interstitial condensation which is the same process describe above however occurs inside your walls or roof (usually hidden), this can lead to mould, mildew & decay hence can affect your health and the buildings structural adequacy.

Most issues with interstitial condensation are caused by us (humans) showering, breathing, cooking, washing & drying clothes inside a house.

As we increase building standards to produce buildings that are warm/cool (temperature difference from inside to outside) & airtight (no uncontrolled air movement, exfiltration/infiltration) we increase the risk of condensation occurring, so we need to be very aware of the materials we specify and how we construct buildings.  i.e. vapour open, vapour closed, what ventilation, what ACH or permeability we are expecting and if condensation does occur how does the building drain it out and how well/quickly the products dry out.

Contact us if you would like further information or help with a project.

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