Naturally it is better if a house can be made proof against mice when it is actually being built. Even the best houses have their weak points where mice can gain entrance, and it is often difficult to find these and render them secure. It is always a good idea to ensure that cellar windows are closed, that window panes are unbroken, and that doors close tightly.
All cracks and holes in the walls that are more than 7 mm across must be covered with fine-mesh netting; this would include ventilation openings. In prefabricated buildings it is important that the joints between the outer sheets are closed, for quite commonly there is free passage up under the lowermost sheets.
Mice can climb up rough vertical surfaces (timber, bricks, cement etc.) and they can often find their way up into a cavity wall and reach the ventilation space under the roof.
A 20 cm wide band of hard, smooth paint, about 1 metre above the floor, will prevent mice from climbing up, and a bent metal plate with an overhang of only 2 cm will have the same effect. Vertical pipes can be fitted with a metal guard which the mice cannot pass. It should be remembered that creepers and other plants growing up a wall make it easier for mice to ascend. •