Closing Up Your Holiday Home in October: 9 Checks That Stop You Finding a Nest of Rodents in Spring

There is one phone call we never get in October, and that we get in droves between 15 March and 20 April.

"We've just opened up the house. There are droppings everywhere in the kitchen, a mattress torn open upstairs, and a smell… I don't even know how to describe it to you."

At that point, there is no longer any conversation to be had about prevention. There is cleaning to do, a mattress to throw out, often insulation to strip out, and an invoice that bears no relation whatsoever to what half a day of vigilance six months earlier would have cost.

Because the moment that decides everything isn't spring. It's the last weekend of October — the one where you close the shutters, empty the fridge, turn off the water and drive away thinking "see you at Easter".

Brown rat hidden in the grass beneath green leaves in a garden

Why an empty house is a rodent magnet

It's tempting to assume that a shut-up house, with no food and no occupants, is of no interest to anyone. The exact opposite is true.

A rodent is looking for three things, in this order: a thermally stable shelter, freedom from disturbance, and only then food. A closed-up country house ticks the first two boxes perfectly. No footsteps in the hallway, no lights, no vacuum cleaner, no dog. And a thermal inertia that, even without heating, keeps the loft and the wall cavities 5 to 10 °C above the outside temperature on a January night.

As for food, a rodent needs very little. The house mouse (Mus musculus) eats around 3 grams a day and can survive a very long time without drinking if its food contains a little moisture. Three grams is what's left at the bottom of a badly re-sealed bag of rice, in the crumbs under a toaster, in a bag of cat biscuits forgotten under the sink.

And all the while, it is breeding. A female can produce 5 to 10 litters a year, of 4 to 8 young each, reaching sexual maturity in 6 to 8 weeks. Between November and April, in a quiet, temperate building, one pair easily turns into thirty or so individuals.

The four species you actually find in April

The dormouse and the stone marten are the two specialities of closed-up country houses, and they are also the two cases where improvising is riskiest: the edible dormouse is a protected species in several European countries and is regulated in France, and the stone marten is classified as a species liable to cause damage depending on the département, with strict rules on trapping. You don't deal with them as you would a mouse. You exclude them; you don't kill them.

The 9-point closing-up protocol

The guiding principle: you don't "protect" a house in October by setting three traps. You make it uninteresting and impermeable. Trapping is the safety net, not the strategy.

1. Genuinely clear out food, including what you assume is inert

Emptying the fridge is second nature. Emptying the dry-goods cupboards, much less so. Rice, pasta, flour, lentils, sugar, savoury snacks, couscous semolina from the summer, pet biscuits, bird seed in the garage: all of it sits there for six months.

Two options: take everything home, or transfer it into airtight glass storage containers with a seal. Thin plastic is no match for the incisors of a mouse, which gnaw continuously and have no trouble opening a bag, a cheap plastic tub or an egg box. Glass, metal and thick PET, on the other hand, do the job.

The unexpected bonus: that same discipline also eliminates pantry moths and weevils, which love flour left somewhere warm for six months.

2. Deal with bedding and textiles before locking up

A mattress torn open in spring isn't the work of a starving rodent, it's a rodent building its nest. Foam, polyester wadding, wool and cotton are perfect nesting materials.

In practice:

• duvets, pillows and blankets go into vacuum storage bags or, better still, into rigid plastic boxes with clip-on lids;
• mattresses are stood up against a wall or protected with a full encasement cover;
• clothes left on site are washed (sweat-laden fibres are far more attractive to clothes moths) and then stored away sealed.

3. Walk the outside of the building with a hand on the wall

The single most cost-effective item on the whole list, and the one people invariably skip because it's raining that day.

A mouse gets through an opening of 6 mm — the diameter of a pencil. A rat, 20 mm. A dormouse, through a badly fitted vent tile.

Inspect the entire perimeter of the building, methodically:

• door bottoms and thresholds (the gap under a garage door is the royal road);
• cable entries, ducting, gas pipes, the water supply, condensate drains;
• crawl-space air vents, often gnawed or working loose;
• tumble-dryer, mechanical ventilation and extractor-hood outlets;
• the roof-to-wall junction, verges, ridge fillers and access flaps.

4. Seal up with the right materials

Expanding foam on its own is useless: a rodent goes straight through it in a night. Silicone likewise.

What does hold:

• fine-mesh metal grille (5 mm max) for air vents and larger openings;
• stainless steel wool for rodent-proofing packed into cable entries and cracks, optionally fixed with mortar or foam;
• metal plates or brush-strip door bottoms with metallised bristles for thresholds.

It has to be stainless steel, not ordinary wire wool: the latter rusts, crumbles and reopens the way in over a single damp winter.

5. Turn off the water, but above all remove any available moisture

Shutting off the mains and draining down is a standard frost-protection reflex. But think too about residual water: traps, shower trays, full watering cans in the utility room, plant saucers, pet bowls, an open rainwater butt against the wall.

A rodent that finds water indoors has no reason left to go back out. And a dry house also sees fewer woodlice, silverfish and mould patches when you reopen.

6. Close off chimneys and flues

An unblocked chimney flue is a vertical motorway for dormice and birds and, in late summer, for the wasp and hornet colonies that build in unused stacks.

A mesh rain cowl on the flue plus a blockage at the bottom (an inflatable chimney balloon or a plate) settles the matter for several years. One warning: if you block the bottom, write it down somewhere — a fire lit in a blocked flue on the first weekend of March ends very badly.

7. Prune, clear, and leave nothing leaning against the façade

A rodent doesn't scale 4 metres of smooth render. It climbs whatever you give it: ivy, wisteria, a walnut branch 80 cm from the roof, a log pile against the wall, a ladder left outside, a rough PVC downpipe.

• Cut branches back to at least 2 metres from the roof (dormice and martens jump, and jump well).
• Move the log pile 5 metres from the house, raised 30 cm off the ground.
• Mow for the last time in late October and clear a 50 cm strip of gravel or short grass at the foot of the walls.

8. Install monitoring, not treatment

This is where we see the most mistakes. Putting five blocks of rodenticide in a house you're about to leave for six months guarantees decomposing carcasses inside a wall cavity, out of reach, with the accompanying smell lasting until June — to say nothing of the risk of secondary poisoning for owls, foxes and neighbourhood cats.

ANSES and the rules governing the use of anticoagulant rodenticides also make clear that these products must not be used permanently or as preventive bait: their use is part of targeted control, baited in secure bait stations, with carcasses collected. None of which is possible in a closed-up house.

The right approach is passive monitoring:

• a few mechanical snap mouse traps, unbaited or lightly baited with peanut butter, set along walls in closed-off areas inaccessible to pets;
• simple "tell-tales": a fine layer of flour or talc on a piece of card in the utility room, the attic, under the sink. When you reopen, the footprints tell you everything in three seconds;
• if a neighbour or caretaker calls by once a month, a quick check of those tell-tales is worth any number of connected sensors.

A word on ultrasonic rodent repellers: the available studies show no lasting effectiveness, as rodents habituate to the signal very quickly. It's no disaster to own one, but it isn't a closing-up strategy.

9. Write it down, photograph it, date it

Five minutes that change everything. Walk round with your phone: a photo of every vent you've blocked, every trap you've set and where it is, the sealed flue, the closed stopcock. Note the list of traps and how many there are on a page in a notes app or a house logbook.

Otherwise, in April you'll find four traps out of six — and discover the sixth the following November, under a chest of drawers, along with its contents.

What to do when you reopen, before you sleep there

The opening-up protocol matters just as much as the closing-up one, for a very specific health reason.

Rodent urine and droppings can carry several pathogens. Santé publique France and the Institut Pasteur document in particular leptospirosis (the bacterium Leptospira, transmitted via rodent urine, especially in damp environments) and, more rarely in mainland France, hantaviruses — haemorrhagic fever with renal syndrome linked to the Puumala virus is well documented in the north-east of the country, with cases reported every year. Hantavirus infection occurs mainly through the inhalation of aerosols from contaminated dust.

The very concrete consequence — and this is probably the most important piece of information in this article:

You do not open up a house that has been shut for six months by running a vacuum cleaner or a broom over dried droppings. Sweeping and vacuuming throw into the air precisely what you must not breathe in.

The right sequence:

1. Throw open doors and windows, and step outside for half an hour. Ventilation is the first line of defence.
2. Put on disposable nitrile gloves and, where there is significant visible contamination in a confined space (attic, crawl space), an FFP2 or FFP3 mask.
3. Dampen the soiled areas with a disinfectant solution (diluted bleach, roughly one part 2.6% bleach to nine parts water) and leave it to work for about fifteen minutes.
4. Pick everything up with paper towel, dispose of it in a sealed bag, disinfect the surfaces, then wash your hands thoroughly.
5. Only then do the ordinary cleaning.

And if opening up reveals an established infestation — a nest in the insulation, marten latrines, gnawed cables — stop right there. Contaminated insulation must be stripped out and replaced, and gnawed electrical cabling is a genuine fire-safety issue: it is a regularly identified cause of fires in the lofts of little-used houses. An electrician needs to check things over before you switch the main breaker back on.

The underlying logic to remember

Closing up a second home works like any serious pest-control strategy, in the same order of priority:

1. Remove the resources (food, water, nesting materials);
2. Physical exclusion (6 mm, stainless steel, mesh);
3. Managing the surroundings (branches, firewood, vegetation);
4. Monitoring (tell-tales, mechanical traps);
5. Chemical treatment — as a last resort, targeted, and never while the property is unoccupied.

That is the exact opposite of what most owners do: they start with step 5 and skip the first four.

Half a methodical day in late October, with a head torch and a roll of wire mesh, spares you the scenario of the shredded mattress, the insulation to redo and the suspect consumer unit. It isn't a matter of luck. It's a matter of 6 millimetres.

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Closing up a house in the Île-de-France or elsewhere in the country, and you already had visitors last winter? An exclusion survey before you lock up — identifying entry points, sealing recommendations, a monitoring plan — takes a single visit. Our teams work with private owners, apartment blocks and property managers.