Rising damp is ground moisture drawn up into porous masonry, such as brick, sandstone and mortar, by capillary suction, usually to about 0.5 to 1.5 metres above ground, according to the NSW Heritage Office. It is often caused by a missing, failed or bridged damp-proof course. Leaks and condensation can look similar, so get the cause diagnosed before you pay for treatment.
- Rising damp normally reaches 0.5 to 1.5 metres above ground level, says the NSW Heritage Office.
- Many 19th-century Australian buildings were built without a damp-proof course (DPC), and some early DPCs failed.
- Garden beds, paths and renders that cover the DPC are a common cause, and are cheap to fix.
- Replacing a ventilated timber floor with a concrete slab on fill can push moisture into the walls.
- Old fixes such as hard cement render are no longer recommended because damp rises behind them.
What is rising damp?
Rising damp is moisture from the ground soaking up into porous masonry walls by capillary suction, much like a sponge. The NSW Heritage Office says it affects stone, brick, earth and mortar, and normally reaches 0.5 to 1.5 metres above ground level.
Most masonry walls have a damp-proof course (DPC) near the base to stop this. A DPC is a waterproof layer built into the wall just above ground. Modern DPCs are usually thin black polyethylene sheet. Older ones used slate, lead, glazed tiles or bitumen. Many 19th-century buildings were built without one.
What does rising damp look like?
Rising damp shows up at the bottom of walls and fades out higher up. The NSW Heritage Office describes these signs:
- A tide-mark stain along the lower part of internal walls.
- Blistering or flaking paint, and loose or crumbling plaster.
- White, powdery salt deposits on the wall surface.
- Crumbling or fretting brick, sandstone or mortar at the base of outside walls.
- Musty smells and mould in rooms with poor airflow.
Salts make it worse. As the water evaporates, salts are left behind and grow as crystals inside the masonry. This is called salt attack, and in severe cases it can slowly destroy bricks and stones.
Rising damp vs condensation vs leaks: how can you tell?
Not all damp is rising damp. The NSW Heritage Office says leaking pipes, failed roofs and blocked gutters are often the real cause. Condensation is another common culprit in Sydney homes with poor ventilation.
| Type | Where it shows | Typical pattern | Usual fix |
|---|---|---|---|
| Rising damp | Base of walls, up to about 0.5–1.5 m | Even band along the wall, salt deposits, tide marks | Remove bridging, improve drainage and ventilation, new DPC if needed |
| Falling damp | Upper walls, below gutters or parapets | Patches below leaks, worse after rain | Repair gutters, downpipes, flashings and mortar joints |
| Penetrating damp from leaks | Near pipes, showers, hot water or air-con overflows | Small, local patches that may not follow rain | Find and repair the leak or failed grout |
| Condensation | Cold walls, windows, corners, wardrobes and bathrooms | Mould and droplets, worse in winter and after showers | Better ventilation, exhaust fans, heating and airflow |
Based on NSW Heritage Office guidance. A specialist should confirm the cause.
Hand-held moisture meters can mislead. The NSW Heritage Office warns that some cannot tell a dry but salty wall from a wet one, so readings need careful interpretation.
What causes rising damp in Sydney homes?
Older Sydney terraces, cottages and sandstone homes are most at risk, especially those built before modern DPCs were standard. Common causes include:
- No DPC, or an old one that has failed.
- Bridging: render, internal plaster, garden beds, paths or raised paving that cover the DPC and let moisture go around it.
- Poor drainage: ground or paving sloping towards walls, and downpipes emptying onto the base of walls.
- Blocked or missing subfloor vents, which trap moisture under timber floors.
- Replacing a ventilated timber floor with a concrete slab on fill. The NSW Heritage Office calls this one of the worst mistakes renovators make, because moisture is forced up the walls.
- Leaking sewer or stormwater pipes near the house.
How do you fix rising damp?
Start with the cause, then pick the least invasive fix that works. The NSW Heritage Office lists these steps in order:
- Diagnose: have the walls assessed to confirm the moisture source and how far it extends.
- Fix the easy causes: repair leaks, gutters and downpipes, and lower garden beds or paths that bridge the DPC.
- Improve site drainage so water runs away from walls.
- Restore subfloor ventilation by clearing or adding vents.
- Manage salts with sacrificial renders or poultices, which absorb salt and are replaced over time.
- Insert a new DPC where damp is severe: by undersetting, sawing a slot and inserting a membrane, or chemical injection.
Chemical injection drills a row of holes along the base of the wall and injects a water-repellent product to form a barrier. The NSW Heritage Office notes that salts left in the wall above still need treatment, and that the product must penetrate the full wall thickness to work.
It says these older treatments have mostly proved unsatisfactory and should no longer be used: hard cement renders, damp-proof mortar additives, ceramic drying tubes and passive electro-osmotic systems.
On reactive clay soils, common in Western Sydney, changing drainage can upset the soil’s moisture balance and cause structural cracking. Get geotechnical or structural engineering advice before major drainage changes. In pre-1990 homes, have old wall linings and floor coverings tested for asbestos before anyone drills or strips them.
How is rising damp treated in sandstone and heritage homes?
Sydney has many sandstone and early brick homes, and these need extra care. The NSW Heritage Office explains the trade-offs between the main ways to insert a new DPC:
- Undersetting replaces sections at the base of the wall and inserts a DPC. It removes salt-laden masonry, but also removes original fabric, which matters for heritage buildings.
- A sawn slot with a membrane disturbs less fabric, but cannot reach under existing floors on internal walls, and salt left above the new DPC needs treatment.
- Chemical injection is the least disruptive, but must penetrate the whole wall and still leaves salts to manage.
Clay poultices and sacrificial renders can draw out or absorb salts. They are designed to wear away and need ongoing care. If your home is heritage listed or in a conservation area, check with your council before altering walls.
How do you stop rising damp coming back?
Even a new DPC can be bridged again. The NSW Heritage Office recommends regular checks and simple housekeeping:
- Keep garden beds, mulch, paving and paths below the DPC line.
- Clean gutters and make sure downpipes discharge into drains, not onto walls.
- Keep subfloor vents clear of plants, soil and stored items.
- Fix leaking taps, pipes and shower grout quickly.
- Slope ground and paving away from the house.
- Avoid hard cement renders at the base of masonry walls.
How much does rising damp treatment cost?
As of October 2026, we could not find a current, reliable Sydney price guide for rising damp treatment, so we have not quoted a range. The price depends heavily on the diagnosis. Fixing a bridged DPC may cost little, while a new DPC along every wall is a bigger job.
Cost drivers to ask about:
- The assessment or inspection fee, and whether it is credited against the work.
- Length of wall treated, often priced per lineal metre.
- Wall type and thickness: solid brick, cavity brick or sandstone.
- Removing and replacing salt-damaged plaster or render.
- Drainage, ventilation and plumbing repairs.
- Making good: skirting boards, painting and moving furniture.
Ask each specialist to list these items separately, so you can compare like with like.
Who should assess rising damp?
Get the problem diagnosed by someone who does not only sell one treatment. A building inspector or damp specialist can assess the walls. For heritage-listed homes, the NSW Heritage Office suggests specialist advice, and a heritage consultant may be needed. If you also see cracking, call a structural engineer.
In NSW, waterproofing work is defined broadly as treatment to stop water or moisture getting into a home, and needs a contractor licence when the job is over $5,000 including GST. Ask which licence your damp contractor holds.
Licence check: look up every contractor on the NSW Government’s free licence check (verify.licence.nsw.gov.au). Make sure the name and licence class match the business on your quote.
Get rising damp assessed by our crew
Describe the damp to MyTradeCrew, including where it appears, how high it reaches and the age and type of your home. We will send it to up to three vetted local trades from our crew who can assess the cause and quote you directly.
Frequently asked questions
Is rising damp serious?
It can be. Left alone, rising damp and salt attack can crumble brick, sandstone and mortar, damage plaster, rot skirting boards and floor timbers, and encourage mould. Most cases can be controlled once the cause is found, so act early and get a proper diagnosis.
Can you fix rising damp yourself?
You can fix some causes yourself, such as lowering garden beds against walls, clearing subfloor vents and making sure downpipes drain away from the house. A new damp-proof course, chemical injection or replastering is specialist work, and a job over $5,000 needs a licensed contractor.
Does damp-proof course injection work?
It can work when the wall is correctly diagnosed with rising damp. The NSW Heritage Office says the product must penetrate the full thickness of the wall, which can be difficult to ensure, and that salts left in the wall above still need treatment.
Is rising damp covered by home insurance?
Cover depends on your policy and the cause of the damp. Gradual problems such as rising damp may be treated differently from sudden events such as a burst pipe. Read your policy wording, ask your insurer, and keep any inspection reports.
Why did damp appear after we renovated?
Common reasons are a new concrete slab replacing a ventilated timber floor, paving or garden beds raised above the damp-proof course, blocked subfloor vents, or hard cement render on the base of walls. A damp specialist can check whether the renovation bridged or bypassed the DPC.
Ready to get quotes?
Compare up to 3 licensed, insured rising damp assessment trades near you. Free.
