Guidelines on rodent proofing measures in buildings

1. Voids provide ideal harbourage and nesting places for rodents.  While voids are sometimes inevitable in a building, the following measures should be considered:
   1. Voids should be made inaccessible to vermin.  The materials and decorative finishes used should be resistant to gnawing by rodents;
   2. There should be no voids between the sides, back or bottom of built-in furniture and the adjacent walls or floors.  Voids greater than 6 mm wide behind wooden skirting should be avoided;
   3. Voids formed by fixing battens behind a panel should be kept to a minimum and made inaccessible to vermin.  The materials used should be resistant to gnawing by rodents; and
   4. False ceiling at places such as kitchens, food-preparation rooms and food stores should be avoided as far as practicable.  If false ceiling is unavoidable (e.g. in offices and shopping centres), ceiling voids should be compartmentalised with rodent-proof materials as far as possible to discourage free movement of rodents.  Metal panels are more preferable.  The gaps between vertical ducts/cables and passing through panels should be less than 6 mm.
2. Holes, openings and gaps at building fabric can be entry points to a building by rodents.  To plug such loopholes, the following measures are recommended:
   1. Rat-holes and other small openings greater than 6 mm should be blocked by filling or covering them with appropriate materials such as fine concrete, cement mortar, 20 gauge sheet metal or 22 Standard Wire Gauge (SWG), barbed wire balls, etc;
   2. Broken or missing gratings should be replaced. Ventilation grids and other similar openings may be proofed externally with galvanised steel woven wire-cloths of 22 SWG at about seven meshes to 25 mm.  These materials exclude both rats and mice;
   3. Gaps at wall openings for the passing through of pipes/wires/ducts should be sealed with metal plates, barbed wire balls or cement; and
   4. Rear exits of buildings should be installed with all-metal doors.  Wooden doors, if used, should be protected at the bottom by fitting a 20 gauge metal “kicking-plate” (at least 300 mm high) on the outside.  This should have a maximum clearance of 6 mm.  A similar plate should be fixed to the door frames to form a continuous band of metal.  Metal “kicking-plates” of the same kind should also be fitted to the wooden doors to other passageways.
3. Rodents may make use of vertical pipes to reach entry points or harbourage places. Guarding against their vertical access can be achieved by the following measures:
   1. Vertical pipes should be spaced at least 100 mm apart and a distance of at least 100 mm should be maintained between pipes and the adjoining wall, such that rodents would find it difficult to climb between a pipe and a wall or adjacent pipes; and
   2. Circular rat guards made of 20 gauge metal sheets with a diameter of at least 300 mm should be employed (if necessary, in the form of inverted funnels) to prevent rats from climbing along building services.  The space between a rat guard and a pipe should not be larger than 6 mm.  It should be ensured that there is no projection or any other structure nearby that can act as a foot step for rodents to jump over the rat guard.
4. Flower beds and surface channels provide rodents with favourable harbourages and dispersal routes.  The following measures should be taken to discourage infestation of rodents :
   1. Flower beds at close proximity to food attractions, e.g. refuse collection points, should be avoided.  External walls of flower bed should not be less than 1 m in height with outwardly bent ledges or copings added on top of all sides.  Wall surfaces should be smooth and without any projection.  High rise vegetation exposing the soil surface should be planted in a flower bed.
   2. Open channels are preferable.  Otherwise, the opening of the grating covering a surface channel should be less than 6 mm in width, or galvanised steel woven wire-cloths of 22 SWG at about seven meshes to 25 mm should be installed underneath the grating.
   3. Openings such as drain holes on flower bed walls, retention walls, drain pipes should be screened with galvanised steel woven wire-cloths of 22 SWG at about seven meshes to 25 mm.
5. Areas such as refuse collection points, markets, loading areas, service rooms, store rooms and kitchens are very susceptible to rodent infestation. Particular attention should be paid to these areas to ensure implementation of comprehensive rodent proofing measures.