Why is draught-proofing important?

Smoke pencil used to identify draughts.

What causes draughts?

Draughts are caused by the uncontrolled air leakage of cold air into the building and cause the loss of heated air from inside through gaps, cracks and holes in the building fabric.

The loss of warmed air through uncontrolled ventilation increases heating costs of a building, since additional energy is required to re-heat the replacement air.