Quick answer: The most common signs of rodents in a loft are scratching or scurrying noises at night, droppings on the boards or insulation, tunnels and nests in the loft insulation, gnawed timber or cables, and a stale, ammonia-like smell. Small, scattered, rice-sized droppings point to mice; larger, spindle-shaped droppings in groups point to rats. Once any active infestation is cleared, the long-term fix is finding and sealing the way in.
Lofts are warm, quiet and rarely disturbed, so they suit mice and rats very well, especially from autumn onwards when it turns cold. We deal with a lot of rodent-damaged lofts across Cardiff and South Wales, and the pattern is usually the same: the pests get dealt with, but nobody seals the entry point, so a few months later they're back.
The signs to look for
Noises
Light, quick scratching or pattering after dark is typical of mice. Rats are heavier, so you're more likely to hear thumping, dragging or gnawing. Noises in the ceiling above a bedroom, or inside a wall near the eaves, are often the first thing people notice.
Droppings
Droppings are the most reliable way to tell what you're dealing with. Public pest control guidance describes them like this:
| Mice | Rats | |
|---|---|---|
| Dropping size | Around 3–6mm, like a grain of rice | Around 20mm, like a large raisin or baked bean |
| Shape and spread | Rod-shaped, scattered widely | Spindle-shaped, usually in groups |
| Body size (adult) | Small, roughly 15g | Much larger, roughly 300g |
| Noise | Light scurrying and scratching | Heavier scampering, gnawing, thumps |
| Other marks | Small gnaw marks; greasy smears where they run in heavy infestations | Dark greasy rub marks along regular routes, larger gnaw marks |
Damage to the insulation
Mineral wool insulation makes a comfortable nest. Look for tunnels and runs through the roll, flattened paths, shredded patches and balls of chewed material mixed with paper or fabric. Rodent-damaged insulation is often wet with urine, compressed and dirty, and it no longer insulates properly.
Gnawed cables and timber
Rodents have to gnaw constantly to keep their teeth in check, and electrical cables are a favourite. Chewed cable sheathing in a loft is a genuine fire risk. If you find bare copper or chewed cables, don't touch them – get a qualified electrician to check the wiring before anything else.
Smell and staining
A musty, ammonia-type smell in the loft or on the landing is a sign of urine build-up, especially with mice. You may also see yellow staining on the insulation or ceiling boards.
How they get into Welsh terraces and semis
Mice can get through a gap roughly the width of a pencil, and rats through a hole around the size of a 10p coin, so you're looking for small openings, not obvious holes. The usual entry points we find in Cardiff and South Wales homes are:
- Gaps at the eaves. Rotten or poorly fitted fascias and soffits, and gaps where the roof meets the wall, lead straight into the loft.
- The cavity wall. In semis and newer homes with cavity walls, mice often climb up inside the cavity from a gap low down and come out at the top into the loft.
- Broken air bricks and service holes. Damaged air bricks, and gaps around gas pipes, waste pipes, cables and the soil stack where they pass through walls, are common ways in at ground level.
- Neighbouring lofts. In some older terraces the party wall in the loft isn't fully built up to the roof or has gaps in it, so rodents move along the row from house to house.
- Ridge and verge tiles. Loose or missing mortar at the ridge or gable ends can leave gaps big enough for mice.
- Extensions and dormers. Where a newer roof joins an older wall there's often an unsealed gap.
- Climbing plants. Ivy and other climbers give rodents an easy route up the wall to the eaves.
Proofing versus pest control
These are two different jobs, and you usually need both.
Pest control deals with the rodents already there, using traps or baits. If you have an active infestation, especially rats, get a pest controller – private, or your local council's service where one is available – to clear it first. Sealing rodents inside your loft just moves the problem into your walls and ceilings.
Proofing stops new ones getting in. It means tracing the routes in and sealing them with materials rodents can't chew through: steel mesh, wire wool packed and sealed over, cement or mortar, and metal-faced bristle strips or eaves combs. Air bricks should be replaced or covered with fine mesh, not blocked, because the floor void still needs ventilating.
Without proofing, pest control tends to be a repeating cost. Without pest control, proofing can trap an active population inside. Our rodent proofing service covers an inspection of the loft and the outside of the house, sealing entry points, mesh where needed and replacing contaminated insulation. We're happy to work alongside whoever is handling the pest control.
Cleaning up and replacing contaminated insulation
Rodent droppings and urine aren't something to sweep up casually. Rat urine can carry leptospirosis (Weil's disease), and dried droppings break up into dust when disturbed.
- Wear disposable gloves, a well-fitting dust mask and old clothes.
- Don't dry-sweep or vacuum droppings with a household vacuum. Dampen them with disinfectant first, then pick them up with paper towels and bag them.
- Disinfect boards, joists and any stored items that have been fouled.
- Wash your hands thoroughly afterwards, and wash clothes on a hot cycle.
Insulation that has been nested in, soaked in urine or fouled with droppings should come out. Bag it in heavy-duty sacks and dispose of it properly. Replace it with new mineral wool, laid to the recommended 270mm depth, once the entry points are sealed – there's no point fitting fresh insulation for new rodents to move into. If you're replacing it anyway, it's a good chance to bring the whole loft up to standard; our page on loft insulation explains how we do it.
If the loft is used for storage, check stored boxes too. Cardboard and fabric are popular nesting materials, and sealed plastic boxes are a much better bet once you've cleaned up.
When to get help
A couple of droppings and one mouse caught in a trap might be a one-off. It's time to call someone if you can hear activity most nights, you find droppings in several places, the insulation has been tunnelled through, you suspect rats, or they keep coming back after treatment. Damaged cables always need an electrician.
If you'd like us to find where they're getting in and put the loft right afterwards, request a free survey. We'll tell you what we find and what it needs, and we won't sell you new insulation if the old stuff is fine.