When damp or mould needs a repair or a professional

Some damp and mould problems can't be fixed by drying the air. If any of the situations below apply, the job is to find and fix the cause, and in some cases to act quickly for safety.

If you suspect carbon monoxide

Headaches, dizziness, nausea, tiredness or confusion when a gas or other fuel-burning heater is running can be signs of carbon monoxide. Health Victoria's advice is to turn the appliance off, open doors and windows, leave the home keeping them open if possible, and seek medical advice straight away (Health Victoria).

If anyone already feels unwell, confused or faint, get everyone into fresh air first. Only turn the appliance off and open windows if you can do it quickly on the way out. If someone collapses or has trouble breathing, call emergency services: 000 in Australia, 999 or 112 in the UK, 911 in the US.

Open-flued gas heaters are sensitive to exhaust fans. A rangehood, bathroom or toilet fan running at the same time can draw carbon monoxide back into the room, so Energy Safe Victoria advises not to run exhaust fans while the heater is on, to keep the room adequately ventilated, not to leave gas heaters running for long periods or when they aren't needed, and to have them serviced at least every two years, including a check for negative pressure (Energy Safe Victoria). Turning the fans off doesn't make a faulty heater safe; the service is what checks that. This applies to open-flued heaters in particular; outside Victoria, check your local gas safety regulator.

Signs the cause is in the building

A stain that is damp to the touch, growing, or comes back after rain.
Mould that returns within weeks of cleaning. Something keeps that surface wet: a cold external wall, poor extraction, or water behind tiles or plaster.
Mould bigger than a dinner plate, spreading onto a second wall, or on plasterboard, carpet or fabric.

About the dinner-plate line

That threshold is ours, and it's deliberately cautious. The US EPA says most people can clean areas up to about 10 square feet (roughly 0.9 m²) themselves, and that absorbent materials like ceiling tiles and carpet may need to be thrown out if they go mouldy (US EPA). Because this site can't see the patch, it only suggests cleaning it yourself when it's small and on a hard surface.

Small isn't always safe to do yourself. The EPA says to call in a professional if the water damage came from sewage or other contaminated water, to get advice first after a lot of water damage, not to run a heating or cooling system you know or suspect has mould in it because it can spread the mould, and to talk to a health professional first if you have health concerns (US EPA).

If you do clean a small patch, the Victorian government's Better Health Channel suggests (source):

Household detergent or white vinegar, with the room well ventilated. Never mix bleach with ammonia, acids or other cleaners.
Rubber gloves, eye protection and a P1 or P2 mask. A mask only works with a good seal, and people with a heart or lung condition should get medical advice before using a P2 mask.
Don't dry brush the mould: it flicks spores into the air.
Pregnant women and children shouldn't do the cleaning or be in the room, and people with weakened immune systems or chronic lung disease may be more at risk.
Mouldy items that can't be cleaned, like cardboard boxes and mattresses, may need to be thrown out.

If you rent in Victoria

This section is about Victoria, Australia only. Who fixes mould depends on its cause. If a problem with the property caused it, it's usually the rental provider's job; if the renter's behaviour caused it, it may be the renter's. Mould or damp linked to the building structure can be an urgent repair when it makes the home unsafe to live in. Tell your rental provider as soon as you see it (Consumer Affairs Victoria). Rentals must also be free from mould and damp caused by or related to the building structure (Tenants Victoria).

Putting it in writing, with a dated photo, gives you a record. Other Australian states, the UK and the US have different rules; check your local renting authority. The same goes for gas safety and mould-cleaning rules: this page draws on Victorian and US sources, which may not be the formal rules where you live.

While you wait for a repair

Keep the area as dry and aired as you safely can.
Don't scrub or disturb large patches.
Keep anyone with asthma, allergies, a weakened immune system or lung disease, and anyone pregnant or young, out of the room where you can.
A dehumidifier can keep the room drier in the meantime. It won't fix the cause.

Sources

Each source below was opened and checked against this page on 30 October 2026.