Guidelines on Rodent-proofing Design in New Building

1. Voids provide ideal harbourage and nesting places for rodents, but it is inevitable to have voids in a building, therefore the following measures should be considered:

   1. The voids should be made inaccessible to rodents, and the materials and decorative finishes being 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 panel should be kept to a minimum and made inaccessible to rodents.  The materials used should be resistant to gnawing by rodents; and

   4. False ceiling should not be installed at places such as kitchens, food-preparation rooms and food shops.  If false ceiling is unavoidable (e.g. in office, shopping centre), ceiling void should be compartmentalised into smaller sections and completely partitioned with rodent-proof material(s) so as to discourage free movement of rodents above the false ceiling.  Metal plate is suggested to be used for partitioning and the gap resulted from the passing of vertical ducts/cables through the metal plates should be kept at less than 6 mm.

2. Holes, openings and gaps at building fabric can be entry points to building by rodents.  To tackle with such structural defects, 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, e.g. fine concrete, cement mortar, 24 gauge expanded galvanised steel or 22 Standard Wire Gauge (SWG) galvanised steel woven wire cloth with mesh size not greater than 6 mm, barbed wire balls, etc;

   2. Broken or missing gratings should be replaced.  Ventilation grids and other similar openings may be proofed externally with 24 gauge expanded galvanised steel or galvanised steel woven wire cloth of 22 SWG with mesh size not greater than 6 mm.  These materials can exclude both rats and mice;

   3. Gaps at wall openings for the passing of pipes/wires/ducts should be sealed with metal plate, barbed wire balls or cement; and

   4. Wooden doors should be protected at the bottom by fitting a 20 gauge galvanised steel ‘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. 

3. Vertical pipes may be used by rats to reach entry points or harbourage places.  Guarding against their vertical movement can be achieved by the following measures:

   1. Vertical pipes should be spaced at least 100 mm apart and also at least 100 mm with adjoining wall such that rodents would find it difficult to climb between a pipe and a wall or adjacent pipes; and

   2. Circular rat guard made of 20 gauge galvanised steel sheet, projecting about 230 mm from the pipe and diameter of at least 550 mm (assuming the diameter of pipe is less than 90 mm) should be deployed, if necessary, in form of inverted funnel to prevent rats from climbing along building services.  The gap between the rat guard and the pipe should not be larger than 6 mm.  Make sure there is no projection or any other structure nearby to serve as 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 bed should not be built at close proximity to places with handy food sources for rodents (e.g. refuse collection points).  External walls of flower bed should be more than 1 m in height with outwardly bent ledges or with copings added on top of the sides.  Wall surface should be smooth and without any projection.  High rise vegetation exposing soil surface should be planted in flower bed;

   2. Open channel is preferable.  Otherwise, grating covering surface channel should have aperture not larger than 6 mm in width, or 24 gauge expanded galvanised steel or galvanised steel woven wire cloth of 22 SWG with mesh size not greater than 6 mm should be installed underneath the grating; and

   3. Openings such as drain holes on flower bed wall, retention wall and drain pipes, etc. should be screened with 24 gauge expanded galvanised steel or galvanised steel woven wire cloth of 22 SWG with mesh size not greater than 6 mm.

5. Areas such as refuse collection point, market, loading/unloading area, service room, store room, kitchen, etc. are highly susceptible to rodent infestation.  Particular attention should be paid to these areas to ensure implementation of comprehensive rodent proofing measures.