If your house smells like something has died but there's nothing to see, the animal is almost certainly in a space you can't see into: the roof, a wall cavity, the subfloor or behind a kitchen appliance. The smell leaks out through gaps that can be metres from the body, so the room where it's worst is a clue, not the answer. Rule out look-alike smells first, then trace it methodically.
First, make sure it's a dead animal
If the smell is more like rotten eggs, treat it as a possible gas leak and don't go searching. The NSW Government's gas safety advice is to leave the building, call 000 and ask for Fire and Rescue NSW.
Next, run water into every drain, including the spare shower and laundry floor waste, because a drain that hasn't been used for weeks can dry out and let sewer air in. Then check the fridge drip tray, under the bin liner and the back of the pantry.
A dead animal smell is heavy, sweet and rotten, builds over days and is usually strongest in one part of the house.
How to trace the smell
Do this first thing in the morning, before windows are opened.
- Score every room out of five, including the laundry, garage and wardrobes. Step outside between rooms, because your nose stops noticing a smell within minutes.
- In the worst room, compare the smell near the ceiling with floor level. Stronger up high points to the roof. Stronger along the skirting boards points to a wall cavity or the subfloor.
- Sniff at every opening: downlights, exhaust fans, air-conditioning vents, the manhole, power points on outside walls and gaps under kitchen kickboards.
- If one fitting seems to be the source, seal around it with painter's tape for a day. If the smell moves to the next fitting, you're following the air path back towards the animal.
- Walk around outside and sniff at the subfloor vents in the brickwork. A strong smell at one vent is a very good clue.
In a semi, terrace or unit, the source may be next door or in a shared roof space, so ask your neighbours or the strata manager.
Signs that point to the exact spot
Flies. Big flies gathering at one window, light fitting or vent often mark the opening nearest the body.
Maggots or stains. Maggots dropping from a downlight, or a new damp-looking brown patch on the ceiling or low on a wall, mean the animal is close.
Recent baiting. If you or a neighbour have put out rat or mouse bait, a carcass indoors is much more likely. The NSW EPA's dead mice factsheet notes that poisoned mice usually retreat to their burrows to die. In a house, that's often a wall cavity or roof space.
Pets and noises. A dog or cat that keeps sniffing at one wall, or scratching in the ceiling that went quiet just before the smell began, tells you where to look.
Where it usually is in a Sydney home
Roof space
Rats and possums both use roof spaces, so start here. A small body can be completely hidden under insulation batts, so look for flattened insulation, droppings and flies around the manhole and downlights. Step only on the ceiling joists and watch for electrical cables.
Wall cavities
Most homes have wall cavities an animal can fall into from the roof and not climb out of. The smell is usually strongest at skirting level and at power points on that wall. If you've heard rats in the walls, the body may be at the bottom of the cavity, which is where a dead rat removal service in Sydney can help.
Under the floorboards
In homes with raised timber floors, a smell that's strongest near the floor and outside at one of the subfloor vents points here.
Behind appliances, in ducts and chimneys
Pull the fridge out and unclip a kitchen kickboard before you assume the problem is inside a wall. If the smell gets worse when ducted air conditioning runs, turn it off; the animal may be in or near the ductwork. Birds and possums also end up in chimneys.
If it might be a possum
Possums are protected in NSW, and trapping a live one without a licence is illegal. For the removal itself, see our dead possum removal in Sydney page.
Why the smell comes and goes
A smell that's bad one afternoon and faint the next morning doesn't mean the animal has gone. Warm weather speeds up decay, air moves between the voids and rooms as the house heats and cools, and exhaust fans and air conditioning can pull void air inside while they run.
How long does the smell last?
There's no fixed timeline. A mouse or rat usually smells for a shorter time than a possum, and heat, airflow and where the body lies all change it. Fluid soaked into insulation, plasterboard or carpet can keep smelling after the body has dried out or been removed, so dealing with those materials is part of ending it. That's what a dead animal odour removal service is for.
Stay safe while you look
NSW Health advises against touching dead wildlife and says never to handle bats or flying foxes. If you must move a small carcass, it recommends a P2 or N95 mask, eye protection, disposable gloves and a shovel or tongs, then washing your hands. The NSW EPA notes that mice can carry leptospirosis and that people who are pregnant or immunosuppressed shouldn't handle dead mice.
When to call in a professional
Get help if you can't narrow the smell down, if it's in a wall, subfloor or part of the roof you can't safely reach, if flies or maggots are coming inside, or if the smell stays after the body is out. If you rent, tell your agent or landlord in writing as soon as you notice it.