Is it a leak, rising damp or a roof problem?
Three causes of a damp wall leave three different sets of signs, and the official pages name them before any cleaning starts: a concealed pipe shows indoors, rising damp shows at the base of the wall, and a roof or gutter fault can show as discoloured or bulging patches, cold or damp to touch, where mould grows in the wall and roof cavities. The table below puts the signs the pages give side by side, so the water can be found before the mould is wiped.
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 Finding leaks on your property, from SA Water.
Three causes, told apart
Each row is one kind of sign, and each column is one cause. A cause the sources do not cover in that row is left saying so.
| Sign | A leaking pipe | Rising damp | The roof or gutters |
|---|---|---|---|
| Where it shows | Indoors: walls, floors or carpets that have gone damp, warped or discoloured, because a concealed leak can run behind a wall or under a floor. | At the base of the wall: NSW Health says rising damp is ground moisture rising up a brick or stone wall, and Homes NSW describes the same moisture travelling up through the bricks or stone of a home. | A roof or gutter fault can show as discoloured or bulging patches, cold or damp to touch, where mould grows in the wall and roof cavities. Queensland’s tenancy authority defines weatherproof as roofing or windows that keep water out when it rains, and requires walls, ceiling and roof to be in good condition and not affected by significant dampness. |
| How it looks | Some leaks announce themselves: a dripping tap, a leaking toilet, a new wet patch on the lawn. Others are not easy to spot, and SA Water says you may not notice until the next water bill. | A damp brick wall. Consumer Affairs Victoria’s buying guide says damp brick walls can indicate rising damp or salt damp, and NSW Health adds that poor sub-floor ventilation or moisture in the sub-floor area will worsen the problem. | Damaged or blocked guttering is on Victoria’s health department’s list of common causes of indoor mould, alongside leaking roofs and walls; 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. |
| Outside signs | Soil that has gone damp, grass with unusually green patches, or paths of brick or concrete left wet, which SA Water lists as signs a leak may be outside the home. | No source here says. | A discoloured or bulging patch that may be cold or damp to touch, which Consumer Protection WA says mould can cause in wall and roof cavities; WA Health’s hidden-mould list adds the roof space itself, where moist air can be vented in but not allowed to escape. |
| Who the source says to call | A plumber. WA Health names plumbers for identifying and fixing plumbing leaks, and Victoria’s removal page says to call one where repairs to damaged pipes and drains are needed. | An experienced building consultant, who NSW Health says can check the damp course and recommend ways to fix the problem. | Builders or roof specialists, whom WA Health names for fixing leaks in the building structure. |
A leaking pipe
SA Water’s leak page is written for householders, and it splits the signs in two. Outside, the signs are damp soil, unusually green grass and wet brickwork or concrete paths; inside, the signs are walls, floors or carpets that have gone damp, warped or discoloured. Some leaks are easy to see or hear, a dripping tap or a leaking toilet among them; others are harder to spot, and they may only come to light on your next water bill.
In the ACT, Icon Water’s page gives a room-by-room order of the same search: the kitchen, the bathrooms and the laundry first, for dripping taps, the connections at washing machines and dishwashers, and damp patches on the walls; then the garden taps, hoses and sprinklers, the hot water system and the air conditioning, and the green or damp patches around the property and under the house.
What the pages say to do next is to have the leak repaired rather than to keep cleaning the wall: WA Health names plumbers for identifying and fixing plumbing leaks, and Icon Water points to the territory’s master plumbers association for a licensed one.
Damp from the ground
Consumer Affairs Victoria’s buying guide lists its structural warning signs under a lead-in about further visits to a property: damp brick walls can indicate rising damp or salt damp. The SA Government’s inspection list names damp brick walls among the structural problems to look for. NSW Health describes the mechanism and the fix: rising damp is ground moisture rising up a brick or stone wall, made worse by poor sub-floor ventilation or moisture in the sub-floor area, and it can be fixed by installing a new dampcourse or waterproof barrier in the wall, with the weep holes and air vents at the base of the home left uncovered.
Water at the base of a wall is not only wet weather’s fault. The CSIRO’s guide to managing termites, which covers the same damp zone under a house, lists the household habits that keep it damp: grading the ground and paving so rainwater flows away from the house rather than towards it, watching for leaks where plumbing or tiling has loosened, keeping garden sprinklers from regularly watering walls and stumps, and directing the drainage from an air conditioner away from the building. The same guide’s householder inspection looks for dampness that shows as discolouration or staining, and names its vulnerable rooms: bathrooms and laundries head the list, along with anywhere drainage is poor, such as paving that sends water at the house.
Under the floor
The floor is where a hidden leak and a damp site overlap, and it is worth a look before any cleaning. NSW Fair Trading’s list for people inspecting a home includes lifting carpet and checking for rotting floorboards or damp, under its heading for internal factors to check.
The Queensland building commission’s guide to flood-damaged timber gives the test for whether damp timber has gone past staining: decay is usually preceded by surface discolouration from moulds or stains, but a stain that scrapes off with a knife to sound timber underneath is not of concern, while timber that has gone spongy under the knife, or that a screwdriver sinks into easily, has decayed. Left damp with air available, the same guide says mould (dark staining) can set in and decay can follow over time, particularly in low-durability timbers such as untreated pine, and the space under a suspended floor has to be drained and dried out immediately once water has been there.
Water from the roof and gutters
The roof is the source the tenancy rules treat as plainly the building’s: Queensland’s minimum housing standards define weatherproof as roofing or windows preventing water from entering when it rains, and require the walls, ceiling and roof to be in good condition and free of significant dampness. NSW Health lists a leaking roof and a blocked rain gutter among the water leaks and plumbing problems to repair.
Gutters carry a share of it. Victoria’s health department names leaking roofs and walls, and faulty plumbing including blocked gutters and downpipes, among the common causes of mould indoors, and says gutters should be cleared and maintained. Consumer Protection WA’s landlords bulletin gives the mechanism: its 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, and a discoloured or bulging patch that is cold or damp to touch is how mould in the wall or roof cavity can show.
The roof space has its own moisture story, and WA Health’s hidden-mould list names it: a roof space where moist air is vented in but not allowed to escape, and roof materials above ceiling tiles that have lost their glaze or are insufficiently insulated. The national home design guide explains how the space is meant to manage it: the risk depends on the interaction of ventilation and insulation, condensation forming on the underside of roofing materials whenever their temperature drops below the dew point, and a cold roof, one with an air space above the ceiling, is required by the National Construction Code to be ventilated. Where it does form, the same guide says it must be drained to the outside of the building so it does not accumulate in insulation and ceiling lining. YourHome’s insulation page adds the two details that decide whether that works: thermal bridges, the pathways where heat bypasses the insulation, need to be identified and insulated to cut both heat flow and condensation risk, and a roof that is ventilated should have air gaps designed in so condensation is carried away or dries out.
Which one is yours?
None of the pages gives a single test that names the cause, and none asks a householder to open a wall. What they give is position. Rising damp shows at the base of the wall; a roof or gutter fault can show as discoloured or bulging patches, cold or damp to touch, where mould grows in the wall and roof cavities; a concealed pipe can show anywhere along its run, and its other signs are outdoors, where the ground stays wet or greener than its neighbours. Where two of those are true at once, the pages agree on the order of work: find the water first, then clean, because a cleaned patch returns while the moisture is still arriving.