In cavity walls, a minimum separation is maintained to ensure unobstructed cavity drainage.

Often, a continuous drainage mat within the cavity is used to deflect the mortar droppings and facilitate a clear drainage path.

The water entering this cavity moves out through the weep holes spaced appropriately at the cavity's bottom and placed above the flashings. 

Additionally, vents near the cavity's top promote air circulation within the cavity and aid in evaporation of cavity moisture.

Flashings can be installed externally to prevent moisture from penetrating the exterior wall, or internally to divert water that enters the cavity back towards the outside.

Internal flashing is installed at the bottom of the cavity and places where the cavity is interrupted.

One end of the flashing is overlapped by a water-resistive barrier provided on the interior wythe, whereas the other end extends beyond the exterior wythe and bends down to form a drip edge to facilitate free fall of water away from the wall.

Sheet metal flashings, asphaltic membrane flashing, composite flashing, and synthetic rubber are the commonly used flashings.