Many traditional properties are built with a suspended wooden floor which sits above a void air space between the perimeter walls and ground. If this space is not ventilated, the air in it becomes stagnant and humid, and the moisture within it begins to condense on the brickwork and flooring. Over a prolonged period, this moisture causes the floor to rot from the underside.
To avoid this situation airbricks must be positioned in the wall such that air can exchange freely between the sub-floor void and the outside. These airbricks are manufactured in terracotta and plastic to approximately the size of a standard brick, and one should be inserted in the wall every 180cm (5ft 11in), on all sides of the property.
New mechanical vents introduce fresh air to the sub-floor and can alternate and extract stale air.