This guide covers keeping mice and rats out before an infestation starts. If you already suspect activity, our identification guides for signs of mice in a home and signs of rats in a home cover what to check and what professional treatment involves.

Why mice and rats move indoors

As outdoor temperatures fall and natural food sources become scarcer, rodents actively seek out shelter, warmth and food in and around buildings. The British Pest Control Association’s guidance on both species describes this seasonal shift directly: rats move toward urban and residential locations as autumn and winter progress, and field mice look for warmer places to nest as the weather turns colder, readily taking advantage of a house’s structure and stores for the winter months (BPCA: Rat control and prevention; BPCA: Mouse control and prevention).

Proofing measures that work

The BPCA’s own proofing advice for mice is specific and practical, and applies equally well to deterring rats:

• Check for gaps larger than 4mm around pipes, cables, doors, airbricks and where utilities enter the building — this is the threshold the BPCA gives for a gap a mouse can exploit. Rats need a slightly larger opening, roughly the size of a 50p coin, but the same inspection routine catches both.
• Fit door sweeps or brush strips to external doors that show a visible gap underneath.
• Store food in airtight containers and clean up food debris and spills straight away, in the kitchen and anywhere pet food or bird feed is kept.
• Cover household waste so rodents can’t access it, and keep bin and compost lids closed.

Garden and yard maintenance

The BPCA is explicit that good yard maintenance is a major factor in deterring rats and mice from moving in for the winter — the aim being to remove everything they need (shelter, warmth, food and water) so the property simply isn’t an attractive place to settle.

• Keep gardens clear and tidy, and cut back overgrown areas where rodents could nest undisturbed.
• Clear piles of wood, building rubble or garden debris away from the house, and off the ground where possible.
• Cover compost heaps and ensure they aren’t holding accessible food waste.
• Store any outdoor rubbish in containers rodents can’t chew or force their way into.

Why rodenticide isn’t the first step

It can be tempting to put down rodenticide as soon as you see the first sign of activity, but the Health and Safety Executive is clear that rodenticides carry a genuinely higher risk than many other pest-control products, in part because of how widely they can affect wildlife that was never the intended target. Anticoagulant rodenticide residues have been found in a wide range of species, and the HSE’s own guidance recommends trying good hygiene practices, physical proofing and traps before turning to chemical control (HSE: Rodenticides).

This is also the reasoning behind the CRRU UK stewardship regime, which places monitoring, training and best-practice conditions on how professionals use rodenticide products outdoors and around buildings, specifically to reduce the risk to non-target wildlife (CRRU UK: The stewardship regime). It’s also worth knowing that GOV.UK restricts what a private individual can lawfully use for pest control — self-locking snares and glue traps designed to catch rodents are prohibited, and any lethal trap or poison must be placed under cover to protect other animals (GOV.UK: Pest control on your property).

If they’re already inside

Proofing and yard maintenance reduce the risk significantly, but they don’t guarantee nothing ever gets in — a rodent that’s already established inside a wall cavity or loft won’t be solved by sealing the entry point after the fact. If you’re finding droppings, gnaw marks or hearing movement, that’s a control situation rather than a prevention one; see our guides on signs of mice and signs of rats, and our guide on DIY prevention versus calling a professional for how to decide between the two.

Sources and further reading

• British Pest Control Association (BPCA) — Mouse control and prevention advice
• BPCA — Rat control and prevention advice
• Health and Safety Executive (HSE) — Using rodenticides
• Campaign for Responsible Rodenticide Use UK (CRRU UK) — The stewardship regime
• GOV.UK — Pest control on your property

Best Pest Control Quotes is an independent guide. We may earn a fee from some links; this never affects what we write.