Typically used to allow an air-space to ‘breathe’, there are a number of types of airbrick. This plastic form is very common on newer builds (one suspects it’s a cost issue!) and work perfectly well but they’re rather easy for rodents to chew on and so work their way into a building. The simple cure is to stuff the resulting hole with stainless steel wire wool but a longer term fix is to either replace the airbrick with a new one or cover the damaged one with a surface mounted version.
Damaged airbrick
