Ventilation for moisture management

Ventilation, it’s not all about breathing fresh air, it’s also about managing moisture.

We introduce a lot of moisture into our homes via bathing, cooking, washing clothes, breathing etc. This moisture ends up in the air and needs to be managed to prevent problems.

Here are just a few stats to give you an idea of the resultant airborne moisture contents attributed to various activities:

  • Shower 0.25 litres per 5-minute shower
  • Clothes dryer 2.2 to 3 litres per load if vented indoors
  • Cooking dinner 0.6 litres (plus 0.75 litres if gas cooking) per family of four
  • Dishwashing 0.35 litres per family of four
  • House plants 0.4 litres per 6 plants

Excess moisture in our homes can result in condensation forming on surfaces. Dampness leads to structural decay and mould growth.

Mechanical ventilation helps prevent these moisture problems by removing the moisture laden air.

In a conversation I had last year with Gord Cooke from Construction Instruction, he said:

“If you insulate the building fabric it needs to be airtight. If it’s airtight the building needs to be ventilated. If it’s ventilated it needs to be airtight.”

The theme here is that airtightness and ventilation go hand in hand. An airtightness control layer helps improve the thermal performance, and helps prevent airborne moisture from entering the building fabric. However, once we’ve prevented the moisture laden air from entering the building fabric it still remains inside the rooms of the house.┬áThe final step is to remove this moisture from the house. The solution is ventilation.

The benefit of having a decent level of airtightness is that the air is contained. Contained air can be controlled. Mechanical ventilation controls the air by moving it along a designated path. Without airtightness, the air path will be uncontrolled through all sorts of gaps and cracks, (building defects) in the building envelope.

There are various ways to implement mechanical ventilation but the easiest and most cost-effective way is to simply install an exhaust fan with a 24hr ventilation capacity. A supply system or a balanced (supply/exhaust) system can also be looked at as part of the whole-house ventilation strategy. The important thing though is that there must be a strategy.

LESSON: Build tight, vent right.