You walk in after a weekend away, notice a smell that wasn’t there on Friday, and spend ten minutes with your head in the laundry cupboard trying to work out what it is. Trust that instinct. Timber floors can sit over damp subfloors, tin roofs make excellent possum accommodation, and holiday houses may sit empty for months. Each can develop a distinctive smell when something goes wrong. Here are nine odours worth investigating, roughly in order of how often they turn up in local homes.
Musty, earthy, “old tent”
The most common complaint of the lot. Between Queensland humidity, Melbourne winters, Auckland damp and the poorly insulated housing stock we’re still working through, mould has plenty to work with, and that musty smell means it’s actively growing, usually out of sight. Check under the kitchen sink, behind the washing machine, inside the bathroom vanity and along the base of wardrobes on south-facing walls.
What to do: Find the water first, or the cleaned patch comes straight back. Tiles and other non-porous surfaces take a diluted bleach solution or a proper mould product. Ventilate and wear gloves. Plasterboard, carpet underlay and MDF are better replaced than scrubbed. Bigger than about a square metre, or can’t find the source? Call a professional. And persistent damp in a rental may well be your landlord’s responsibility under healthy homes rules, worth raising in writing.
A wild, doggy smell — and you don’t own a dog
Congratulations: you have tenants. Usually that’s a brushtail possum that’s found a gap under the eaves or a lifted sheet of roofing iron, though rats will do the same job. Either way, they’re using your ceiling cavity as a bathroom. You’ll often hear them first. Heavy thumping at dusk and again before dawn is the classic possum calling card.
What to do: Check the law before you touch anything. Where possums are protected native wildlife, you can’t trap or relocate one yourself, and moving a possum out of its territory is usually a death sentence for it anyway. The safe route is a licensed operator, a possum box nearby as alternative housing, then sealing the entry point once the animal is out. Wherever you are, the sealing-up matters most, and make sure whoever does the job checks for young.
3. Sewer, or “public toilet”
Sewer gas coming back into the house can include hydrogen sulphide and methane, neither of which you want indoors. The cause is often beautifully simple: every shower, basin and floor waste has a U-shaped trap holding a little water, and that water is the only thing between you and the sewer. Leave a bathroom, laundry or holiday house unused for weeks and it evaporates, which is why people so often notice it the moment they open up the bach.
What to do: Pour a jug of water down every drain, including the laundry floor waste and the spare bathroom. A teaspoon of vegetable oil on top slows future evaporation. If that doesn’t fix it, you’re likely looking at a blocked vent pipe, a cracked pipe under the slab or a dried-out gully trap outside. That’s a plumber’s job.
A sweaty, gym-bag smell
Ruled out the sneakers by the back door? Look at your air conditioning. Condensation collects on the evaporator coil of split and ducted systems, and in the humid in-between weeks of autumn and spring it becomes a very comfortable home for bacteria. Switch the unit on and it blows that smell through the house.
What to do: Start with the filters. Most units let you pop them out and wash them in two minutes, and almost nobody does it as often as the manual suggests. If the smell survives clean filters, the coil itself needs doing, with a proper coil cleaner or by a technician. An annual service before summer pays for itself in running costs.
Ammonia, or “cat wee”, and there’s no cat
A sharp, slightly metallic smell that catches the back of your throat has a few possible sources: a cleaning product, a leaking ammonia-based coolant in an older fridge or freezer, or mould. Most often, though, it’s something that has died in a wall cavity, under the floor or in the roof, a smell that peaks a week or two in, then fades over the following month.
What to do: A dead rodent isn’t dangerous, but it means you have a pest problem to solve rather than an odour to wait out. If you can narrow it to one spot, a pest controller can often retrieve it. If you can’t, ventilate hard, keep the area dry and let time do the rest. Then seal the entry points before next winter.
Stale cigarette smoke in a house nobody smokes in
Most of us know about secondhand smoke. Thirdhand smoke is the newer concern: the residue left when tobacco particles settle into carpet, curtains, walls and bed linen and stay there. It’s what you smell in an old rental or a house bought from a long-term smoker, and researchers have identified a number of carcinogens among those settled compounds. Small children are the most likely to be affected, crawling on the carpet and then putting their hands in their mouths.
What to do: Air the place out, then clean rather than mask. Sugar soap on walls and hard surfaces, curtains laundered or replaced, carpets steam-cleaned, cupboards wiped out inside. In bad cases, sealing and repainting is what finally does it. Scented sprays won’t help. They add a second smell on top of the first.
Rotten eggs — treat this as an emergency
Natural gas has no smell of its own. Mercaptan is added specifically so you’ll notice a leak, and it’s designed to smell like rotten eggs because that’s an odour humans react to instantly. LPG, which is what plenty of homes off the gas network run on, is odorised the same way, with one important difference: it’s heavier than air, so it pools low, in cellars, under floors and in trenches.
What to do: Don’t investigate. Leave straight away, taking everyone with you, and on the way out don’t flick a light switch, use the landline, start the car in the garage or light anything. Any of these can make the spark you’re trying to avoid. Turn the gas off at the meter or bottle only if it’s safe on the way past. Once you’re well clear, call your gas distributor’s 24-hour faults and emergencies line. The number is on your gas bill and usually on the meter itself. If anyone feels unwell or there’s immediate danger, call 000 or 111 first, and don’t go back in until you’re told it’s safe.
Burning or smoky — with nothing burning
An occasional whiff of smoke with no obvious source is not something to file under “must look into that”. If you notice it when a particular light, powerpoint or appliance is running, you may have overheating wiring behind a wall or in a ceiling fixture. Older homes with original wiring, aluminium wiring or decades of DIY additions are more prone to it.
What to do: Switch off the circuit at the switchboard if you can identify it, and call a licensed electrician immediately. If you can see smoke, or the smell is getting stronger, get everyone out and call 000 or 111. This is not a wait-until-Monday job. While you’re at it, check your smoke alarms: working, tested regularly, with batteries you’ve actually replaced.
Sharp and fishy near a powerpoint
No seafood in the house but you’re picking up something fishy or acrid? The likely culprit is an electrical component overheating. Many of the plastics and flame retardants used in wiring, powerpoints and appliance housings give off exactly that odour as they heat and begin to break down. It’s the smell of melting insulation, an early warning of a fire.
What to do: Follow your nose. If you can trace it to an appliance, unplug it and stop using it until it’s been checked. Heaters, powerboards, older whitegoods and cheap unapproved chargers are the usual offenders. If it’s coming from a powerpoint, a switch or the switchboard, turn off that circuit and call a licensed electrician, and leave that powerpoint alone in the meantime.
The rule of thumb: if a smell is new, if you can’t explain it, and if it doesn’t go away after a good airing, it’s telling you something. Most of the time it’s a dried-out drain or a filter that needs a wash. Occasionally it’s the thing that saves your house.
