Build Tight – Ventilate Right

The aim of airtightness requirements is to save energy. Excess natural and uncontrolled ventilation of air leakage means that heat required for ventilation increases. Excess ventilation air must be heated to room temperature meaning higher energy costs.

Leaks can also cause local draughts which then means that there is a higher room temperature to maintain comfort levels. If these draughts are reduced, then the temperature in the room doesn’t need to be as high. Air leakage can cause localised cooling inside sections of external wall construction causing a sensation of radiation draughts.

The risk of moisture damage is greater in houses with balanced ventilation than in house with exhaust air ventilation. Even a small amount of positive pressure can cause moist air to leak through pervious structures, potentially causing condensation

There are different ways to building houses however it is mainly concrete and timber. Concrete houses tend to have leakage problems confined to joints around windows and doors and well as junctions between roofs and outside walls. In timber houses there is a vapour barrier to use to achieved airtightness. To produce airtightness the construction details must be planned with greater care.

Airtight houses – which can be defined about 1 air change/hour at 50Pa – energy savings that can be achieved are at a good margin compared to non-airtight houses. When ventilation is satisfactory in all rooms and can function well it can be controlled and regulated to the required level in each section of the dwelling. Those dwellings that are less airtight, don’t function as well and then can lead to problems such as condensation and mould

In very insufficient airtight houses, uncontrolled air supply through leaks in the house can result in only certain rooms being ventilation in an acceptable manner. Only in sufficiently airtight houses can the ventilation be controlled and regulated to the required level in each section of the dwelling. Airtight houses are also necessary if heat recovery from the ventilation system is to function well and profitably.

Standards and knowledge of how a functioning ventilation system is to be designed for different airtight houses is incomplete. A considerably greater degree of collaboration between installation and building technology is necessary if we’re to produce low-energy houses with good air quality.

Source: Article submitted by Dr Arne Elmroth, Professor at the Royal Institute of Technology. Stockholm

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