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Mould when you are buying a home

Damp is easier to see before the furniture arrives. NSW Fair Trading’s inspection list points at damp or mould along skirting boards, walls and ceilings and warns to be cautious of paint jobs used to cover up mould, and it says to lift carpet and check for rotting floorboards or damp. Consumer Affairs Victoria and the SA Government each put damp brick walls on their list, with Victoria’s page naming rising damp or salt damp as what they can indicate.

General information from official health, building and housing sources, not advice about your home, your health or your tenancy. The page behind most of this one is Inspecting a home before buying, from NSW Fair Trading.

Water from a leaking roof, reaching the ceiling: NSW Health lists a leaking roof and a blocked rain gutter among the water leaks and plumbing problems to repair.Water from a gutter fault, into the top of the outside wall: Consumer Protection WA’s list of what a landlord should do to avoid mould developing includes cleaning and maintaining the gutters, so rainwater stays out of the roof cavity.Where a roof or ceiling leak shows: NSW Fair Trading’s own inspection list says to check for damp or mould along skirting boards, walls and ceilings.Where a gutter fault shows: a discoloured or bulging patch that may be cold or damp to touch, in the wall or roof cavity (Consumer Protection WA). Shower steam, and the bathroom exhaust fan the building code sizes: the 2025 National Construction Code sets a minimum exhaust flow rate, 25 litres a second for a bathroom or sanitary compartment.Signs in a wet area: the SA Government’s inspection list says to look for mouldy walls, lifting tiles, peeling paint or pools of water. Moist air reaching cold window glass: the national home design guide says condensation forms when humid air meets a cooler surface, such as a window in winter.Condensation and mould on the window: the national home design guide says aluminium frames form a thermal bridge into the home and are prone to condensation.Moist air reaching the outside wall behind a wardrobe: one of Homes Tasmania’s tips for a dry, well-aired home is to allow space between furniture and the wall so air can flow, and it calls this very important with wardrobes.Mould on the outside wall behind the wardrobe: one of Homes Tasmania’s tips is not to stack boxes or other items against outside walls, especially walls that do not get a lot of sun.A small patch on a bedroom wall: NSW Health says it is good to remove mould as soon as it appears. Water from a concealed pipe leak, down inside the wall: SA Water says damp, warped or discoloured walls, floors or carpets can suggest a concealed leak indoors.Where a concealed leak shows: Icon Water says to look in the kitchen, bathrooms and laundry for dripping taps, washing machine and dishwasher connections, and damp patches on the walls. Flood water in the home (the line marks no depth): Victoria’s health department says flooding can cause excessive mould growth, which has to be cleaned up before moving back in.A floor joist with staining or decay: the Queensland timber guide says a surface stain that scrapes off to sound timber underneath is not of concern, while wood that is soft and spongy or easily penetrated has decayed. Damp rising from the ground into the base of the wall: NSW Health says rising damp is ground moisture rising up a brick or stone wall.Where rising damp shows: the base of the wall and the skirting, where Consumer Affairs Victoria says damp brick walls can indicate rising damp or salt damp.Damp ground under the floor: Homes NSW says rising damp is moisture from the ground travelling up into a home through the bricks or stone in its walls.A damp subfloor: NSW Fair Trading’s inspection list says to lift carpet and check for rotting floorboards or damp. Water from a leaking roof, reaching the ceiling: NSW Health lists a leaking roof and a blocked rain gutter among the water leaks and plumbing problems to repair.Water from a gutter fault, into the top of the outside wall: Consumer Protection WA’s list of what a landlord should do to avoid mould developing includes cleaning and maintaining the gutters, so rainwater stays out of the roof cavity.Where a roof or ceiling leak shows: NSW Fair Trading’s own inspection list says to check for damp or mould along skirting boards, walls and ceilings.Where a gutter fault shows: a discoloured or bulging patch that may be cold or damp to touch, in the wall or roof cavity (Consumer Protection WA). Shower steam, and the bathroom exhaust fan the building code sizes: the 2025 National Construction Code sets a minimum exhaust flow rate, 25 litres a second for a bathroom or sanitary compartment.Signs in a wet area: the SA Government’s inspection list says to look for mouldy walls, lifting tiles, peeling paint or pools of water. Moist air reaching cold window glass: the national home design guide says condensation forms when humid air meets a cooler surface, such as a window in winter.Condensation and mould on the window: the national home design guide says aluminium frames form a thermal bridge into the home and are prone to condensation.Moist air reaching the outside wall behind a wardrobe: one of Homes Tasmania’s tips for a dry, well-aired home is to allow space between furniture and the wall so air can flow, and it calls this very important with wardrobes.Mould on the outside wall behind the wardrobe: one of Homes Tasmania’s tips is not to stack boxes or other items against outside walls, especially walls that do not get a lot of sun.A small patch on a bedroom wall: NSW Health says it is good to remove mould as soon as it appears. Water from a concealed pipe leak, down inside the wall: SA Water says damp, warped or discoloured walls, floors or carpets can suggest a concealed leak indoors.Where a concealed leak shows: Icon Water says to look in the kitchen, bathrooms and laundry for dripping taps, washing machine and dishwasher connections, and damp patches on the walls. Flood water in the home (the line marks no depth): Victoria’s health department says flooding can cause excessive mould growth, which has to be cleaned up before moving back in.A floor joist with staining or decay: the Queensland timber guide says a surface stain that scrapes off to sound timber underneath is not of concern, while wood that is soft and spongy or easily penetrated has decayed. Damp rising from the ground into the base of the wall: NSW Health says rising damp is ground moisture rising up a brick or stone wall.Where rising damp shows: the base of the wall and the skirting, where Consumer Affairs Victoria says damp brick walls can indicate rising damp or salt damp.Damp ground under the floor: Homes NSW says rising damp is moisture from the ground travelling up into a home through the bricks or stone in its walls.A damp subfloor: NSW Fair Trading’s inspection list says to lift carpet and check for rotting floorboards or damp. The whole houseSee the house

What the buyer pages say to look for

The three columns are the buyer pages this guide can set side by side: New South Wales', Victoria’s and South Australia’s. Where a page does not name a sign, the cell says so.

Signs of damp and mould, by state buyer page
SignNew South WalesVictoriaSouth Australia
Walls and skirtingDamp or mould along skirting boards, walls and ceilings, under its internal-factors list. Damp brick walls, which its guide says can indicate rising damp or salt damp. Damp brick walls, under its list of signs of structural problems.
CeilingsThe same line covers ceilings: damp or mould along skirting boards, walls and ceilings. No source here says.No source here says.
Wet areasDamp in all wet areas is one of its internal checks, and it adds the hot water system’s size and age to the same visit. No source here says.Mouldy walls, lifting tiles, peeling paint or pools of water in wet areas.
Subfloor and timberLifting carpet and checking for rotting floorboards or damp. No source here says.No source here says.
Painted-over patchesBe cautious of paint jobs used to cover up mould. No source here says.No source here says.

What the pages do not cover

The official pages set out the inspection a buyer makes themselves: Victoria’s guide puts its structural signs under further visits to check whether repairs are needed, and the SA Government’s list sits under inspecting a property.

What the pages say about testing for mould is the other half of the answer. NSW Health says that since most mould is visible it is generally not necessary to test for mould in the home, though some contamination may sit in cavities or the ceiling; where a buyer thinks there is mould but cannot find the source, the same page names the occupational hygienist, who can run specialist mould tests and give advice for a fee. Victoria’s health department agrees that testing is generally unnecessary where mould is visible, and adds the warning that not all mould is visible.

And where the signs point at the base of a wall, NSW Health names the trade for that question: an experienced building consultant, to check the damp course and recommend ways to fix the problem.

If the plan is to rent it out

For a buyer who plans to rent the property out, rules wait on the other side of the purchase. NSW Fair Trading requires a rental property to meet seven minimum standards, and to be fit to live in a property must, at a minimum, be structurally sound, have adequate ventilation, and have adequate plumbing and drainage. Victoria’s minimum standards go further than a checklist item for this subject: all rooms must be free from mould and damp caused by or related to the building structure.

Is it a leak, rising damp or a roof problem?

When should you call a professional about mould?