Checking Your Home Sub-Floor Ventilation

Copyright (c) 2015 Matt Reardon

When your home has excessive sub-floor moisture, it may lead to rising levels of dampness, wood rotting, bad odours and infestation by pests. Left untreated, the consequence of sub-floor moisture might be mould and mildew growth potentially causing serious health concerns.

Often, sub-floor ventilation is a forgotten component of your home maintenance and management. The Building Code of Australia (Vol. 2) requires that sub-floors located between the ground and a suspended floor be ventilated. This minimizes moisture which assists in thwarting timber decay and in creating an environment which discourages termite invasion.

Humid air and moist soil under your subfloor could lead to a number of structural complications, including:

- Flooring products and subfloor timbers absorbing moisture, leading to bent boards plus other damages as your wood fibres begins to swell
- Increased probability of termite invasion, because subterranean termites thrive in moist conditions
- Possibility of fungal decay

To be effective and well ventilated, your sub-floor construction ought to:

- Be free of any vegetation growth and construction debris
- Provide cross ventilation
- Have no dead air spaces
- Have openings that are evenly spaced
- Be well graded to prevent water pooling
- Be done above the outside ground level

There are several ways that moisture is able to seep into the ground below your building floor. Perhaps your building is having some problems of drainage that allows rainwater to begin pooling against your external wall and slowly seep through. It is also possible that you have garden beds that have been built up against your outside wall such that even during the dry season, moisture is seeping through whenever you water the garden.

It is possible that your building is older, giving possibility of downpipes that broke down or got blocked long time ago or whose ground levels that have shifted over the years. You perhaps undertook some house renovations that could have blocked off your subfloor air vents or altered the airflow under your house.

The Australian Building Codes and your local council regulations have specified the minimum standards to be observed for your subfloor ventilation designs, storm water drainage and ground level grades. It is therefore wise to familiarize yourself with these provisions.

Building Code Of Australia (BCA) And Australian Standards (AS) Requirements

- Australian Standard 3660 stipulates the minimum clearance needed between the underside of your subfloor and the ground. This Standard, called 'Termite management' in addition sets out a variety of best practices in building to avoid termite attack and maintain sufficient ventilation. The BCA works in conjunction with the Standards.

- The open space between permits free movement of the air inside your subfloor cavity. It in addition enables you to climb in and conduct an inspection for possible fungal decay, termites' infestation and any other structural problems.

- The Australian Standard requirement set for the air vents spacing is that they ought to be placed inside 600 mm of your building floor corners and be placed evenly around your building perimeter walls.

For more information regarding proper maintenance of your ventilation requirements, we would recommend that you have a look at a very handy booklet that has been published by the Australian Timber Flooring Association (ATFA) titled 'Timber Flooring'.


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MouldBuster has been doing home ventilation in Australia for long. As a systems engineer, Matt Reardon knows what is best for your type of building. Visit MouldBuster and Matt will guide you through the available options. To read more about Matt advice and their services logon to http://mouldbuster.com.au/sub-floor-ventilation/ .