Physical Abilities of Rats and Mice
Both rats and mice can:
•    run along or climb electrical wires, pipes, fences, poles, ropes, cables, vines, shrubs, and trees to
    gain entry to a building
•    climb almost any rough vertical surface, such as wood, brick, concrete, weathered sheet metal,
     and many plastic products;
•    crawl horizontally along or through pipes, augers, conveyors, conduit, and underground utility and
      communications lines;
•    gnaw through a wide variety of materials, including lead and aluminum sheeting, window
     screens, wood, rubber, vinyl, fiberglass, plastic, and low-quality concrete or concrete block.

Rats can:
•    crawl through or under any opening higher or wider than 1.3 cm
•    climb the outside of vertical pipes and conduits up to 7.6 cm in diameter; climb the outside of
     larger pipes attached to buildings by bracing themselves between the wall and the pipe; climb the
     inside of vertical pipes, wall voids, or earthquake safety seams and joints between 3.8 and 10.2 cm
     in diameter;
•    jump from a flat surface up to 91 cm vertically and as far as 122cm horizontally;
•    drop 15 m without being seriously injured;
•    burrow straight down into the ground for at least 91 cm;
•    reach as high or wide as 33 cm;
•    swim as far as 800 m in open water, dive through water traps in plumbing, and travel in sewer
     lines against a substantial water current. In areas where high rat populations exist, it is common
    for both roof rats and Norway rats to enter buildings through toilets and uncovered drains.

House mice can:
•    enter openings larger than 0.6 cm;
•    jump as high as 46 cm from a floor onto an elevated surface;
•    travel considerable distances crawling upside-down along screen wire;
•    survive and reproduce at a temperature of -4oC if adequate food and nesting material are
     available.

Rats can gain entry through holes larger  1.3 cm; mice can use holes larger than 0.6 cm.

Survey for Entry Points
When inspecting sites for potential rodent entry points, look for rub marks, droppings, tracks, gnawing, or other  rodent signs. Special attention should be paid to areas discussed under Common Rodent Entry Points (below). Keep in mind the physical abilities and behavior of the particular rodents, especially their tendency to seek shelter  behind, under, or in appliances, sinks cabinets, drawers, stored goods, wall voids, false ceilings, and other undisturbed areas.
To conduct a thorough survey, inspectors will need an inspection form and paper for noting and illustrating items needing attention; a good flashlight; a mirror (to see under and behind objects); and screwdrivers and other small hand tools to remove interior and exterior vent grills, appliance base plates, and service doors to attics, crawl spaces, and utility cabinets. A tape measure is usually necessary when  preparing a plan and estimating materials needed for repair. A small dustpan, broom, and some lime, flour, or similar powdered material are useful in preparing an area for a follow-up observation of fresh tracks. A camera can be of great value, especially when trying to design a project after leaving the site, or when seeking assistance from someone unfamiliar with the site.  A simple item to use when measuring gaps under doors or around pipes, screens, or vents is a common wooden pencil or ball-point pen (usually 0.5 to 1.0 cm in diameter) — large enough for mouse entry.