A woman in Dapto rang me on a Thursday having spent four days trying to work out where the smell was. Monday it was in the hallway. Wednesday it was strongest in the ensuite. By Thursday morning her husband was convinced it was coming out of the back bedroom and had already been up in the manhole twice with a torch and found nothing.
Nothing had moved. The rat was on the flat of the ceiling above the hallway the whole time, roughly where she'd first smelled it. What changed was which windows were open, whether the ducted heating had run overnight, and which exhaust fan had been going. A ceiling cavity is one big connected space with air moving through it, and the smell comes down wherever there's a gap — a downlight cut-out, a cornice line, the gap around an exhaust fan housing. So it turns up in a different room depending on the day.
That's the part nobody tells you, and it's why people cut holes in their ceiling in the wrong place.
Roughly how long you're in for
A rat in a roof void in August is usually about two weeks of smell, and the worst of it is days four to ten. In February it's shorter and much more intense, because heat speeds the whole thing up. A mouse might be four or five days and you'd only notice it in a small room.
A possum is a different order of magnitude. Bigger animal, more of it, and if it's died down a wall cavity you can be looking at six weeks and a stain that comes through the plasterboard. That's also usually the point at which people find out they had a possum rather than a rat, which is a conversation I've had more than once — the two get confused constantly, and there's a rundown of how to tell them apart in what you can and can't legally do about a possum in your roof.
If someone tells you a dead rodent smell will be gone in a couple of days, they're guessing.
Finding it
Three things narrow it down before anyone lifts a tile.
Blowflies are the most reliable. If there's a cluster of them at one window and none anywhere else in the house, the source is in or above that room. They hatch out and go for the light, and they'll do it in the same spot for days.
Second is where it's strongest at a specific time, not in general. Early morning, before anyone's opened a door or run a fan, is the honest reading. Middle of the day with the house aired out tells you almost nothing.
Third is the runs. Rodents don't wander a roof void at random. They use the same beams and the same insulation channels every night, and after a few weeks those runs are visible — flattened batts, greasy rub marks on the timber, droppings concentrated along one line. Follow the busiest run and you usually get there. Whatever killed the animal, it did it somewhere on that route.
Wall cavities are the hard ones. There's no access, so it comes down to sounding along the wall, working out which stud bay it's in, and cutting one neat hole low down rather than exploring. I'd much rather spend an extra half hour narrowing it before cutting than cut three holes and find nothing.
What we can get to, and what we can't
Roof voids and subfloors, yes, if there's access and it's safe to be in there. Wall cavities, yes, with a cut and a patch. Under a concrete slab or inside a sealed bulkhead, sometimes not, and I'll tell you that on the day rather than after.
We're a pest business, so this is rodents. If something larger has died under a deck or in a stormwater pit, that's a different call — your council handles dead animals on public land, and a general waste or restoration contractor is the right trade for the big ones.
The other thing worth saying plainly: getting the body out is half the job at most. Something died in your roof because something was living in your roof. If nobody deals with that, you'll be having this conversation again in autumn. Removal, baiting, trapping and the walk around the outside to find the ways in all belong to the same visit, which is how we run rodent control, and the entry-point list for older places around here is in rodent-proofing an older Illawarra home.
The bit about supermarket bait
A fair share of these calls start with a bucket of bait blocks from the hardware, thrown into the roof space in a handful of spots.
It works, in the sense that rodents eat it and die. The problem is where. Bait laid loose in the middle of a roof void kills animals wherever they happen to be when it catches up with them, which is often the furthest corner of a wall cavity. Placed properly, in lockable stations on the runs and near the entry points, they're far more likely to end up somewhere reachable — and a lot less likely to end up somewhere a dog can get at it.
There's also a slower cost to loose bait. Anything that eats a poisoned rat carries some of that dose, which is why the owls and the neighbour's cat are part of the calculation and why we're fussy about product choice and placement rather than volume.
The health question
The smell itself is unpleasant and not much else. What matters more is what leaves the body.
Fleas and mites don't stay on a dead host. They move out looking for the next warm thing, which is why a dead rodent in a ceiling is sometimes followed a week later by bites on people sleeping in the room below. If that's happening, say so when you ring, because it changes what we bring.
Rodents also carry leptospirosis, which is spread through urine rather than the carcass, and it's the reason the roof void gets treated as a job for gloves and a proper mask rather than a quick look in a t-shirt. NSW Health's leptospirosis fact sheet covers how it's actually transmitted. Anyone applying pesticide in a roof for money also needs a current pest management technician licence from the EPA, and that licence sits with the person, not the business.
While you're waiting
Air it out properly rather than sealing the room up. Open the windows in the affected room and one at the other end of the house so there's a through-draught, and run the exhaust fans.
Odour neutralisers and bags of charcoal make the house liveable. They don't shorten anything. Same with the gels people put in the manhole — useful for getting through a weekend, not a fix.
And don't cut the ceiling because the smell was strongest there this morning. Ask me how I know.
The Dapto job took about forty minutes once I was in the roof, most of it spent following the run rather than searching. The rat was on the flat of the ceiling near a downlight transformer, which is warm and is where a sick rodent goes. It had eaten bait that had been thrown loose up there in June by someone who never came back to check.
If you've got a smell you can't place, ring us and describe it: which room, what time of day it's worst, whether there are flies at a window, and how long it's been going. We cover the whole coast, and you can check where we work if you're at the far end of it.
Need a hand with this in your home? Get a free quote or call 0430 007 651.