Why use covers?

Wasps and drones are eager to build their nests in the wall cavity. Wasps will need as little as 5 mm (1/6 inch) to gain access. Once a nest is build one cannot remove it. Moisture and cold will find there way to the inner wall. Result: mould!

Mice will use the wheepholes to enter into your house. Once in the cavity, they will always find an opening in the innerwall. In fact mice seldom use doors and windows to enter houses. A mouse can enter through a 9 mm (1/3 inch) wide opening!