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Sub Floor Ventilation

Damp Under The House

Surface water or water in the soil outside of the house will gravitate to under a house and result in the soil beneath the house becoming wet. The degree of water or dampness can depend on the type of soil on the property and the proximity of rock. That dampness remains under the house and will slowly penetrate through a timber floor and create a damp smell within the building. Asthma sufferers will be affected by the damp smell, as well as the extent of moisture in the air within the building. In prolonged situations, the dampness can result in fungal decay of the structural floor framework, flooring and affect the internal furnishings.

The requirements of the Building Code of Australia for sub-floor ventilation must:

  • Be cleared of all building debris and vegetation
  • Be cross ventilated by means of openings
  • Contain no dead airspaces
  • Internal walls (for cavity brick construction) have evenly spaced openings to internal walls
  • Be provided with adequate clearance
  • In older buildings, such as attached terraces or any construction where a party (dividing) wall or structural wall is provided, then it is not possible to have natural airflow or cross ventilation. This often results in dead airspaces where there is no airflow and usually results in mould growing on the soil directly under the house.

The moisture in the area below your house will more easily penetrate through a timber floor rather than through the perimeter brick walls. This moisture, particularly during winter, can be the cause of condensation mould within the house.

What to do about sub-floor ventilation?

The answer to which sub-floor ventilation system is best will depend on the type of construction of the building and the amount of mould and dampness below. There is no one product that fits all problems.

In some houses, it will only require upgrading of the perimeter vents to the sub-floor of a house. Where there are obstructions or party walls, then a solare fan or ducted system will be required.

For more information on what system best suits your building and if other factors are causing dampness, contact our office for independent advice or a building inspection by one of our professional consultants.

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