Should Cavity Walls Be Ventilated?

Traditional cavity walls do not require ventilation. They are designed to be weathertight (airtight and watertight) in order to be thermally efficient and keep moisture out of the wall cavity.

Should a cavity wall be vented?

Cavities don't need to be ventilated. The weep vents are there to allow moisture to drain out at certain locations - eg. round the cavity tray over a lintel or at DPC level.

Do cavity walls need to breathe?

It is also important to remember that buildings need to "breathe" and they rely on constant air circulation. In cases of poor cavity wall installation, essential air vents have been blocked with insulation which consequently impedes the flow of air through the home.