Rising Damp: What It Is, Why It Happens, and How to Spot It Early

Rising damp isn’t just a surface issue, it’s a sign that moisture is moving up through your walls from the ground. If left untreated, it can damage finishes, weaken structural elements, and lead to poor indoor air quality. While it’s uncommon in new builds, it’s still worth understanding the causes and how it’s addressed, especially if you’re renovating or inspecting a property before purchase.

Rising damp occurs when ground moisture travels upward through porous building materials like brick, stone, or mortar via capillary action. It’s most common in homes without a proper damp-proof course (DPC), or where that barrier has been compromised over time.

Common causes include:

• Missing or deteriorated moisture barriers
• Poor site drainage or land sloping toward the home
• Soil, render, or paving built up over the protective layer
• High water tables or seasonal flooding
• Inadequate subfloor ventilation or internal moisture control

Older Homes (Pre-1980s)

In Newcastle, heritage terraces, miners’ cottages, and early brick homes in suburbs like Cooks Hill, Hamilton, and Tighes Hill are often affected.
In Lake Macquarie, fibro and timber homes from the post-war era are vulnerable, especially in low-lying areas like Boolaroo, Cardiff, and parts of Warners Bay.

Before the 1980s, moisture control wasn’t consistently addressed in residential construction, and building codes didn’t require damp-proofing.

Recent Builds

Rising damp can still occur when:

• The DPC is damaged or incorrectly installed
• Landscaping or renovations raise ground levels above the barrier
• Poor drainage or high water tables overwhelm the system

Coastal soils and clay-heavy ground across the region can hold moisture, increasing risk in flood-prone zones like Dora Creek and parts of Belmont.

Whether you’re living in a home or inspecting one to buy, look for:

• Tide marks or staining on internal walls (usually up to a metre high)
• Peeling paint, bubbling plaster, or warped skirting boards
• Musty smells in enclosed or poorly ventilated areas
• Salt deposits (efflorescence) on brickwork or render
• Crumbling mortar or rotting timber
• Mould growth low on walls (distinct from condensation-related mould)

These signs don’t always mean rising damp, but they’re worth investigating, especially if they appear in combination.

Rising damp doesn’t just affect your walls, it affects your wellbeing. Damp environments create ideal conditions for mould, bacteria, and other microorganisms to thrive. Over time, this can lead to:
• Respiratory issues like coughing, wheezing, or asthma flare-ups
• Skin irritation and allergic reactions from airborne mould spores
• Fatigue, headaches, and brain fog linked to poor indoor air quality
• Increased risk for vulnerable groups, including children, elderly residents, and those with compromised immune systems

According to NSW Health, mould exposure can trigger asthma attacks and, in rare cases, lead to serious lung infections. If symptoms worsen at home and improve when you’re away, it’s worth investigating moisture issues.

A damp-proof course is a thin, waterproof barrier built into the wall near ground level. Its job is to stop moisture from creeping upward through bricks, mortar, or stone.

In Australia, DPCs became standard in new builds from the 1980s. Many older homes either don’t have one or rely on a barrier that’s deteriorated over time. Even in newer homes, rising damp can still occur if the DPC is bridged by soil or paving, or compromised by poor drainage.

We’re not suggesting you pepper your building designer or builder with a thousand questions. A good custom home builder will have these details covered. But if something feels off, or if you’re buying a home and want peace of mind, these checks matter:

• Is there a damp-proof course (DPC) installed and visible? The DPC is a physical barrier that stops moisture rising through walls. It should sit just above ground level and remain unobstructed.
• How is water managed around the slab or footings? Surface water should flow away from the home, not pool near the slab. Simple things like sloping paths or gravel strips can make a big difference
• Are garden beds, paving, or render sitting above the moisture barrier? If landscaping or finishes sit too high, they can trap moisture against the walls. Ideally, there should be a visible gap between ground level and the DPC.
• Is ventilation adequate in subfloor areas or enclosed spaces? Poor airflow can lead to condensation, mould, and timber decay. Look for vents or weep holes, especially in older homes or enclosed decks.
• Has external render bridged the damp-proof course?  If the render extends below the DPC, it can act like a sponge, drawing moisture upward and bypassing the barrier. A separation cut line should be made once rendering is complete and before painting to prevent moisture transfer.

Rising damp isn’t easy to fix once the home is built, so it’s worth confirming the basics as the project progresses.

Professional Solutions

• Injecting a damp-proofing cream to form a new moisture barrier is one of the most effective and minimally invasive methods. At Nexus Built, we use Cream Damp Proof Course by Tech-Dry Building Products – an Australian-made, water-based silane/siloxane cream designed to permanently stop rising damp in masonry walls.
• Replastering with salt-retardant materials helps prevent recurring surface damage once the moisture is blocked.
• Replacing the DPC is possible in some cases, but it’s more invasive and typically reserved for severe or inaccessible areas.
• Improving subfloor ventilation or installing moisture barriers can support long-term prevention, especially in homes with timber floors.

Maintenance Tips

• Lowering external ground levels to expose the DPC
• Installing ag lines or improving surface grading
• Keeping garden beds and paving clear of external walls
• Using breathable paints and finishes inside the home

At Nexus Built, moisture management starts well before the slab is poured. We assess site conditions, plan for drainage, and install damp-proof courses with care. We also work closely with landscapers and designers to ensure finishes don’t compromise moisture protection. Your garden beds and paving should complement the build, not undermine it.

Today’s standards include:

• Mandatory DPCs under the National Construction Code
• Drainage plans required for development approval
• Slab edge protection and moisture barriers in slab-on-ground homes
• Subfloor ventilation systems in raised homes
• Landscaping planned to avoid bridging the moisture barrier after handover

We don’t just build to code, we build for quality, health and longevity. That means thinking ahead, communicating clearly, and making sure every detail supports the health and durability of your home.