Rats in the attic

What you are probably dealing with

Noise in a roof space in the evening, heavy enough to be audible through a ceiling, usually means roof rats. They are excellent climbers, they prefer to be high, and an attic is warm, dry and undisturbed.

Quick discrimination:

• Roof rats: active at dusk and before dawn. Noise moves horizontally along joists. Droppings 12-20 mm with tapered ends. Gnawed cable, shredded insulation.
• Mice: lighter, faster scratching, rice-grain droppings. Common in wall cavities more than open roof spaces. See mice in walls.
• Squirrels: active in daylight, especially early morning, and much noisier. Droppings similar in size to rat droppings but rounder.
• Birds: rustling and scratching near the eaves, and it stops after dark.

Mice vs rats settles the rodent question properly.

Go up before you buy

Take a strong flashlight, gloves, and a mask. Look for:

• Rub marks along the top plate and where joists meet the wall — greasy dark smears, unmistakable.
• Droppings in lines along the joists rather than scattered.
• Runs in the insulation: compressed tracks between the bays.
• Shredded material collected somewhere sheltered — that is a nest.
• Gnawed cable, which is the reason not to leave this a month.
• Daylight at the eaves, the gable ends, or around a vent. That is the way in.

Ventilate before you spend long in there, and do not disturb dry droppings while you look.

Trapping a roof space

• Set on the joist runs and along the eaves, where the rub marks are. Not out in the middle of an insulation bay.
• Perpendicular to the run, trigger toward the direction of travel, in pairs.
• Pre-bait unset for three to five nights. Neophobia applies just as much up here. The full sequence.
• Six traps is a sensible number for a typical roof space with established activity.
• Mark where you put them — traps genuinely get lost in an attic, and a forgotten sprung trap under insulation is unpleasant to find two years later.

This is the situation where electronic rat traps most earn their price. Releasing a snap bar over a dead rat, lying flat between joists, is a job people postpone — and a sprung trap catches nothing while it waits. An electronic trap tips out into a bag with an indicator light telling you from the hatch whether it is worth going up.

Finding the climb and closing it

Roof rats get in high. Walk the outside and look up:

• Overhanging branches within about two meters of the roof. This is the most common route by a distance, and cutting them back is often the single most effective thing you will do.
• Gaps at the eaves and soffit joints, particularly where a soffit meets a wall.
• Damaged or missing vent mesh, gable vents especially.
• The gap where a cable or a pipe enters near the roofline.
• Missing tiles, lifted flashing, damaged fascia boards.
• Ivy or a trellis running up the wall — a ladder that grows.

Close gaps with hardware cloth or mortar, not with expanding foam alone. And do it after the trapping, not during: sealing a roof space with rats in it leaves you with rats that cannot get out, which is a much worse problem than rats that can.

The insulation question

Honest answer: it depends on how bad it is.

• Light contamination — droppings in one area, no strong smell — can be spot-cleaned. Dampen, lift, bag, and top up the insulation.
• Heavy contamination, a nest, or a urine smell through the ceiling means removal and replacement of the affected area, and that is usually a professional job with proper respiratory protection and containment.

Do not compromise on this because removal is expensive. Rodent-contaminated insulation in an occupied home with a forced-air system is a genuine air-quality issue, not an aesthetic one.

Cleaning up safely

Attic clean-ups are the textbook case for rodent hygiene guidance, because the space is unventilated and the material is dry.

1. Open the hatch and any vents and ventilate for at least 30 minutes before entering.
2. Gloves. Do not sweep and do not vacuum dry — both put particles into the air.
3. Spray droppings and nesting material with a disinfectant or a bleach solution and leave it to soak for five minutes.
4. Lift with paper towel, double-bag, and bin.
5. Wash hands thoroughly afterwards.

For a large quantity of droppings in a confined space, stop and get a professional with proper respiratory protection. The CDC guidance linked below is specific about when that line is crossed and it is worth reading before you start rather than after.

When to call someone

• A large droppings load across the roof space.
• A nest you cannot reach, or activity inside a sealed soffit run.
• Structural or electrical damage — gnawed cable is a fire risk and wants an electrician's eyes.
• Activity that returns within weeks of a clear run, which means the entry has not been found.