Musty smell in the house: finding hidden water damage

A musty smell with nothing visible usually arrives before the stain does. The federal health guidance is plain: if you can smell mould but cannot see it, find the source.

Read from primary sources · Editor-reviewed · Current as at 20 September 2026

By the waterdamagequotesau.com editorial team · Published 20 September 2026 · Last reviewed 20 September 2026 · 7 min read

8 primary sources cited on this page. How we check what is on this site

A musty smell with nothing visible is one of the most useful warnings a house gives, because it usually arrives before the stain does. The Australian Government’s environmental health committee says it plainly: some mould is not visible, and you may need help if you can smell it but cannot see it. The job is to find the water.

Where the smell comes from, and how to check

Common hidden sources of a damp or mouldy smell, and the first check for each.
Where	What usually feeds it	First check
Behind a shower or bath wall	A failed membrane or grout	Skirting and wall base in the next room; leaking shower
Under carpet	Underlay that stayed wet after a leak or spill	Lift a corner; press the underlay
Inside a wall	A slow leak from a pipe or fitting	Water meter test with every tap off; meter reading at the wall base
Ceiling or roof space	A roof leak, or an upstairs bathroom	Look up with a torch; ceiling damage
Subfloor	Poor ventilation, a leaking pipe, ground moisture	Vents clear; a look underneath if there is access
Wardrobes and corners on outside walls	Condensation on cold walls	Back of the wardrobe, behind furniture

The water meter test is the cheapest diagnosis there is: turn every tap and appliance off, read the meter, wait an hour without using water, read it again. If it has moved, there is a leak on your side of the meter, and in every utility’s rules read for this site that pipe is the owner’s — see plumbing and blocked drains.

What the health guidance says

enHealth, Potential health effects of mould in the environment, p 3 · undated; Wayback Machine copy of 11 July 2026, read 2 October 2026

Because some mould is not visible: it may be in a roof space, behind a wall or under floor coverings. The guidance describes a mould smell as “often a dirty or earthy smell”, says to clean mould you can see or smell and find and control the source of the dampness, and sums up: “remove mould where present, find it when you smell it, repair and control sources of excessive moisture”. It points to an occupational hygienist to locate mould by inspection if you can smell but can’t see it.

The state health departments say the same thing in their own words. NSW Health points to an occupational hygienist where you cannot find the source; the Tasmanian Department of Health names mould you think is there but cannot find as a case for one. SA Health’s note that if mould returns there may be an underlying problem is the other half: a smell that comes back after cleaning is a source that has not been found.

Cleaning the smell away does not help. Air fresheners, bleach on the visible surface and opening windows reduce the smell for a day or two; the source is still wet, and the enHealth guidance is to find and control the source of the dampness so mould does not recur after cleaning. The order is: find the water, stop it, dry what it wet, then clean or remove what grew.

The smell also tends to be strongest where the air is still and the surface is cold: inside wardrobes on external walls, behind beds pushed against a wall, under sinks, in a bathroom with no working exhaust fan. Those are condensation sources rather than leaks, and their fix is ventilation and heat rather than plumbing. The health departments’ prevention advice — run exhaust fans, open windows when the weather allows, keep the inside warmer than outside on cool days — is aimed at exactly that.

Get the source found and dried

Four digits, and restoration companies advertising for your postcode call you back. Ask for moisture readings, not just a clean.

Smell without sight is the situation the health departments carve out. Even so, the aim is to find the moisture, not to count spores: enHealth says we do not recommend testing for mould at all, because there are no health guideline values to compare results with (enHealth (Environmental Health Standing Committee, Australian Government), Potential health effects of mould in the environment, p 3). An inspection that uses a moisture meter and a thermal camera to locate the wet material is more useful than an air sample that confirms mould exists. Mould testing covers what to ask an inspector; hipages publishes an inspection at $150–$350.

Hidden damage and the insurance claim

Damage found by smell has usually been going on for a while, and that is the difficult part of the claim. The listed event is a sudden escape of liquid from fixed pipes or apparatus (Insurance Contracts Regulations 2017 (Cth) reg 19(1)(a)(vi)); the exclusion is wear and tear, rust or corrosion (Insurance Contracts Regulations 2017 (Cth) reg 19(2)(b)), and a policy may have its own wording on gradual leaks. What helps: the plumber’s written cause, the failed part, photographs of the extent, and the date you first noticed. Making the claim sets out what to send.

After the source is found

Fixing the leak stops the supply; it does not dry what is already wet. The wall cavity, underlay or subfloor has to be dried to a reading, and material that has grown mould is cleaned or removed. On the published rate card, drying one room over the three-day minimum is $1,260 excluding GST. Mould removal covers the clean-up, and the cost page the drying.

Common questions

What causes a musty smell in a house?

Mould and damp. The Australian Government's enHealth guidance describes a mould smell as often a dirty or earthy smell, and says some mould is not visible because it is in a roof space, behind a wall or under floor coverings.

What should I do if I can smell mould but can't see it?

Find the moisture. enHealth's guidance is that you may need to consult a professional if you can smell but can't see it, and it names occupational hygienists for locating mould by inspection. A moisture meter and a look at the likely sources come first.

Do I need a mould test if the house smells musty?

This is the one case the health guidance points to for professional inspection: mould you can smell but cannot find. enHealth still does not recommend testing for mould in general, because there are no health guideline values to compare results with; the aim is to find the source, not to count spores.

Is a musty smell dangerous?

The smell is a sign of mould and damp, which enHealth says can trigger nasal congestion, sneezing, coughing, wheezing and respiratory infections, and worsen asthma and allergies, particularly in people with weakened immune systems, allergies, severe asthma or lung disease.

Will insurance cover hidden water damage I found by smell?

It depends what made it wet. A sudden escape of water is a listed event; a slow leak that has run for months is where the wear and tear and gradual deterioration arguments happen. Photograph the source and get a plumber's written cause.

Where does a musty smell usually come from?

From wherever water is getting in or condensing out of sight: a slow leak in a wall or under a shower, a subfloor with poor ventilation, a roof space, wet carpet underlay, or a wardrobe on a cold external wall.

Sources cited on this page

Every figure above was read from the source it is attributed to on 20 September 2026. How we check this.