Rats in the house: why they come in for winter, and how to keep them out

Rats do not hibernate. When the weather turns cold and food outdoors becomes scarce, they look for shelter, warmth and something to eat, and our homes offer all three. That is why calls about rats under floors, in wall cavities and in lofts rise every autumn and stay high through the winter.

01Which rat is it?

Almost every rat problem in a British home involves the brown rat (Rattus norvegicus). It is a strong swimmer, a capable climber and an expert burrower, and it lives in drains, banks, under sheds and anywhere near a reliable food source. The black rat, or ship rat, was once common but is now very rare in the UK.

02Why rats come indoors in autumn and winter

Through spring and summer, rats live and feed outside. As the weather cools, crops are harvested, vegetation dies back and food becomes harder to find. Heavy rain can also flood burrows and drive rats above ground. A house gives them steady warmth, dry nesting sites and, very often, food: kitchen scraps, pet food, bird seed and bins.

Once inside, rats favour quiet, undisturbed spaces: lofts, wall cavities, the voids under floors and behind kitchen units, garages and outbuildings. They breed all year where conditions allow, so a pair that gets in during the autumn can be a much larger problem by spring.

03Signs of rats in the house

• Droppings. Dark and capsule-shaped with blunt ends, about 12 to 20mm long, often in groups along walls and near food.
• Noise. Heavier scratching, scurrying and gnawing than mice make, in the loft, walls or under floors, mostly at night. Rats also squeak, chatter and grind their teeth.
• Gnawing. Teeth marks on timber, plastic pipes, skirting boards, food packaging and cables.
• Smear marks. Dark, greasy marks along walls, joists and pipes where rats brush past on the same route night after night.
• Nests. Shredded insulation, paper, cardboard and fabric in hidden corners.
• Smell. A strong, stale ammonia smell, especially in enclosed spaces.
• Footprints and tracks in dust, and holes appearing in floors or walls.
• Pets. Dogs and cats sniffing, pawing or staring at the same spot under an appliance or along a wall.

Lighter, quicker movement and much smaller droppings point to mice instead. Our guide on telling rats from mice explains the differences, and our guide to common household noises covers the other things that go bump in the night.

04The damage rats do

A rat's front teeth never stop growing, so it has to gnaw constantly to keep them worn down. Rats chew through timber, plastic pipes, insulation, sealants and even soft metals. Inside a house that leads to:

• Fire risk from chewed electrical cables in lofts, walls and under floors.
• Leaks and water damage from gnawed plastic water and waste pipes.
• Structural damage to timber, flooring and the brickwork and soil around foundations where they burrow.
• Spoiled belongings in lofts and garages, and contaminated insulation.

Many home insurance policies exclude damage caused by vermin, so it is worth checking yours and acting early.

Rats also carry disease. They spread leptospirosis, salmonella and other infections through their urine and droppings. Our guide to diseases spread by rats covers the risks and the precautions.

05How to keep rats out

• Seal the gaps. A rat can get through a gap of about 15mm, and it will gnaw at a smaller hole to enlarge it. Check around pipes and cables, under doors, at air bricks and vents, where extensions meet the house, and at the base of walls. Use materials rats cannot chew: wire wool set in mortar, galvanised mesh, metal kick plates and brush strips. Keep air bricks working by meshing them, never blocking them.
• Check the drains. Make sure inspection covers fit and are not broken, and that disused pipes have been sealed. Our guide to rats in drains explains why this matters.
• Remove food. Store food and pet food in sealed metal, glass or rigid plastic containers. Never leave food out overnight, and pick up pet bowls after meals.
• Manage the bins. Use bins with tight lids, keep them closed and away from the house, and do not leave bags of rubbish on the ground.
• Compost carefully. Use an enclosed bin away from the house and keep meat, dairy and cooked food out of it.
• Feed birds with care. Use trays, clear up spilled seed before dark and store seed in metal bins. Our guide to rats in the garden has more on bird feeders, chickens and compost.
• Tidy the outside. Cut back shrubs, ivy and overhanging branches that give cover or a climbing route to the roof, and clear rubbish, timber and garden waste away from the walls.
• Declutter. Lofts, garages and sheds full of cardboard and old fabric give rats places to nest unseen. Store things in lidded plastic boxes and check these areas regularly.

Smell-based deterrents such as peppermint oil or ammonia are often suggested. There is little evidence that they keep rats away, and they do nothing about food or a gap in the wall.

06Why acting early matters

Rats breed quickly, and every week they spend in a building means more droppings, more gnawing and more to clean up afterwards. Over-the-counter poison used in a house can also lead to rats dying in wall cavities and under floors, where the smell can last for weeks. Our guide to dealing with dead rodents explains what that involves.