Rising damp is often thought of as a problem limited to century-old cottages or unsealed brick homes. But the truth is, it’s still very much a problem in modern Australian housing—just harder to spot early. With today’s homes built tighter and more thermally sealed than ever before, airflow has decreased, while moisture retention has increased. That means water doesn’t always get in from outside—it also gets trapped inside.
New builds, renovations, and even well-insulated homes are all at risk if the sub floor isn’t properly ventilated. And because most homeowners don’t regularly inspect under their floors, the long term effects of mould often go unnoticed until damage has already taken hold.
Rising damp happens when moisture from the ground moves upward through walls or floor structures. It doesn’t need a flood or visible leak to start—just consistent ground moisture, poor airflow, and the absence of a reliable barrier system. Over time, that moisture starts to absorb into building materials like timber, brick, plaster and insulation.
While the name suggests a dramatic process, rising damp usually appears gradually. The most common early signs are crumbling skirting boards, bubbling paint near the floor, musty odours, or persistent mould on lower walls. By the time you see these symptoms of rising damp inside your home, the problem under your floors may already be widespread.
Today’s homes are often built on concrete slabs or sealed timber frames, which creates a sense of confidence around moisture control. But sealing a house tightly also reduces natural airflow—and that’s where the risk starts. Without enough ventilation in the sub floor area, humidity builds up beneath the flooring, creating a perfect environment for damp to develop slowly and invisibly.
Newer homes built in high rainfall regions or on sloping blocks are especially vulnerable. Even homes with well-designed drainage can experience problems if the underfloor space doesn’t have adequate cross-ventilation. And when that stale, damp air has nowhere to go, it starts to affect the materials directly above it.
Many homes—new and old—don’t have enough passive airflow under the floor. This can be due to poor design, blocked vents, ground level changes over time, or the use of modern materials that don’t breathe well. Infill developments and tight boundary spacing also limit how much air naturally circulates under the house.
What’s more, renovations often reduce ventilation without meaning to. Extensions, paving, raised garden beds or enclosed verandas can all restrict airflow beneath the house, increasing the risk of trapped moisture and poor drying conditions. Once that happens, even a relatively dry area can develop mould and decay under the surface.
Fixing the visible signs of rising damp—repainting walls, replacing skirting boards, treating mould—isn’t enough if you don’t deal with the root cause. Without addressing moisture in the sub floor, those problems will return again and again. And if left unchecked, rising damp can weaken structural timbers, attract termites, and trigger expensive building damage.
Installing targeted sub floor ventilation systems is one of the most effective ways to reduce moisture damage. By improving airflow beneath your home, you allow damp areas to dry naturally, which protects internal surfaces and reduces long-term repair costs.
These systems are often simple, quiet and energy-efficient. Some rely on passive ventilation, while others use fans or ducting to pull fresh air in and push stale air out. The right setup depends on your home’s layout, location and level of risk—but the goal is always the same: to keep the sub floor dry, breathable and healthy.
Even if your home looks dry on the surface, there are a few subtle warning signs that shouldn’t be ignored. These include persistent mould in corners, musty odours that don’t go away with cleaning, cold or damp-feeling floors in winter, or visible condensation on lower-level walls. You might also notice allergies flaring up more indoors, or find that rugs and furniture develop mildew over time.
If you live in a home built in the past 20 years and assume you’re safe from rising damp, it’s worth getting a professional to inspect your sub floor. In many cases, early-stage moisture problems can be fixed easily—before they turn into a much bigger and costlier issue.
