31/08/2026
💧 Where does the underfloor moisture really comes from?
When we think about moisture inside a home, showers, cooking, breathing and drying clothes usually come to mind. However, homes with suspended timber floors may also have a significant moisture source beneath them.
Rainwater, leaking pipes, inadequate drainage and surface-water runoff can introduce liquid water into a subfloor. Even without a visible leak, moisture can evaporate naturally from exposed soil and enter the subfloor air as invisible water vapour.
According to publicly available household-moisture data and building-science estimates, exposed soil beneath a suspended floor may release up to 40 litres of water vapour per day for every 100 m² of floor area.
For comparison, common indoor activities—including breathing, cooking, showering and drying clothes, can collectively produce around 10.65 litres of water vapour per day.
The actual amount will vary between homes depending on:
• The area of exposed soil
• Soil and ground-moisture levels
• Recent rainfall and drainage
• Subfloor temperature and airflow
• Plumbing leaks or other water sources
• Whether an effective ground-moisture barrier is present
Humid air contains water vapour. When it meets a surface cold enough to reach the dew point, some of that vapour can become liquid condensation.
If damp conditions persist, homeowners may begin to notice musty odours, condensation, discoloured timber, damaged insulation or visible mould.
Spring is a useful time to inspect beneath your floors after Tasmania’s colder, wetter months. Look for standing water, damp soil, signs of water entry, damaged insulation and changes to the condition of the timber.
Underfloor moisture does not always have one simple cause. Identifying and addressing leaks, drainage problems and other sources of water should always come first.
