Apparatus 110 for preventing vermin 124 access to buildings through drainage conduits. The apparatus comprises: a duct 112 defining a flowpath and a barrier 116 which prevents access to vermin through the drainage conduit. The barrier includes a protective structure 125 to deter vermin gnawing the through the barrier. The barrier is movable between a flowpath closed position and a flowpath open position. The barrier is biased to the closed position by a threshold force and is movable to the open position upon application of a force greater than the threshold force. The threshold force is sufficient to maintain the barrier in the closed position under its own weight. The protective structure may be embedded in a matrix, comprise spiky formations, be a hairy or fibrous material, comprise an electric conductor material connected to an electric current source or be a vermin deterrent substance. The barrier may be a membrane barrier such as a duck bill valve. One or more barriers may be used.
