Ventilation Sub-Floor

Sub Floor Ventilation

Extended basement walls after dig out. Ventilation will need consideration.

Sub floor ventilation is essential for the health and longevity of any building or structure with a sub floor area. If your sub floor is damp, musty, mouldy or smelly or you have fungi growing – you need under floor ventilation! 90% of construction was carried out this way prior 1980 before slab on ground became popular.

Constant high moisture levels may cause irreversible damage to the structure of your house. High humidity and poor indoor air quality will severely impact the health of occupants if it finds it’s way into habitable spaces. This can be prevented by good design, but if you find your house lacking you may need to install additional sub-floor walls vents or fans.


  • Mildew
  • Condensation
  • Mould
  • Damp Sub Floors making storage hazardous
  • Rotting Floor Joists Posts or stumps
  • Breakdown to Internal Walls & Paintwork rising damp migration upwards
  • Crumbling Brickwork, salt attack evident if you see white efflorescence.
  • Breeding Ground for Termites, White Ants
  • Rotation and subsidence of floor piers and subwalls especially if moisture is coming up from the ground
  • Cracking of brick walls internal and external due to ground settlement and heave

If adequate cross ventilation can’t be achieved to provide sufficient airflow to keep the sub floor ground dry then mechanical forced ventilation will be required.

Fan forced ventilation can be hard wired and set with timers or humidity switches. However a smart way to go if possible is to use a solar fan. It will only run when the sun shines so that only relatively dry air will be introduced to the sub floor. Other set ups may introduce wet air and exacerbate the problem.

Under house excessive moisture is something best underpinning has to deal with routinely in it’s job of sub floor maintenance.