Your home can fall prey to mould at any time of the year. But during winter, poor ventilation, uneven indoor heating and the chill outside make homes especially vulnerable. It may be a small patch at the back of a cupboard you never open, or a whole room covered in spores.

So what causes mould, what are your rights if you’re a renter or an owner, how much does it cost to have mould cleaned professionally, and is it worth it?

What causes mould?

Simply put, moisture causes mould. “People have no idea how much a little water can do,” says Dr Heike Neumeister-Kemp, chief mycologist (mould expert) from Mycolab. A leaky roof, broken pipes, cracked roof tiles, windows left open while it’s raining or a flood can cause moisture to enter your home. Or you could be creating the moisture within the home itself: through air drying clothes indoors, running appliances without an exhaust, or by under- or over-heating your home in the winter or over-cooling it in the summer.

It’s important to figure out what’s causing your mould problem and to fix the underlying issue, otherwise it will continue to occur, regardless of how thoroughly you may think you’ve cleaned.

What’s the problem with having mould?

Moulds can give off toxic chemicals, called mycotoxins, and if there’s a lot of mould it can be dangerous – possibly resulting in hypersensitivity or allergic reactions, and asthma and flu-like symptoms.

Who’s responsible – landlord or tenant?

So you’ve moved into a new place. You didn’t realise mould would be an issue, but there it is, behind the bed, in the bathroom or dotting the kitchen ceiling. What can you do?

Landlord’s obligations

Throughout Australia, landlords have a general obligation to ensure the homes they lease out are in a reasonable state of cleanliness and fit for habitation by the tenant. As a result, if mould is caused by a leak in the roof, a faulty pipe or gutters or other structural faults, your landlord is responsible for fixing it and remediating the damage.

Tenants’ obligations

That being said, not all mould is caused by structural issues.

  • Tenants may be contributing to or creating the problem themselves by failing to regularly air out and clean the house, allowing condensation to build up in the home, or getting the carpet wet.
  • Tenants also have an obligation to inform landlords or their leasing agents if there’s a problem with the property, for example a window that doesn’t seal or a leaky pipe.
  • If a tenant has caused the underlying problem that led to mould developing, or hasn’t informed their landlord of an issue with the property, they could be held responsible for mould damage and may have to compensate their landlord.

There are still plenty of grey areas, according to Neumeister-Kemp, who often acts as an expert witness in court cases that deal with mould damage.

With no clear-cut responsibility laid out in law, landlords may not accept they’re responsible for mould, forcing tenants to go through housing tribunals or the courts, which takes time and, in some cases, money.

“At the moment, it’s up to a judge to decide whether the mould is bad enough and whether the issue is with a building defect and therefore the owner is at fault,” Neumeister-Kemp said. “Real estates don’t help at all … The tenant gets hit with fines [for ending a lease early] or having to pay for a clean up, and the owner gets sued, because the real estate didn’t tell the tenant or the owner about a fault like a leaky pipe. Now something that would have cost $2000 to $3000, becomes a $30,000 to $90,000 claim.”