Domestic ventilation systems

Do the many domestic ventilation systems regularly advertised on television meet the Building Code?

Domestic ventilation systems are mechanical ventilation systems with a fan that moves air around a house, flat or apartment. Typically, they draw air from the warmer roof space and force it into the living space below. Delivery of air into the living space creates a slight positive pressure and the air escapes from the building through the openings in or around windows and floors.

Claimed effects of these systems include healthier homes because of reduced internal moisture and less mould, fungi and dust mites.

Building Code Compliance

The Building Code (Clause G4) requires ventilation with outdoor air to maintain air purity. Compliance Documents contain several solutions for achieving this. The main solutions are natural ventilation comprising 5 percent of the floor area in opening devices or mechanical ventilation to achieve an air change in the occupied spaces (such as living areas) every three hours.

Because domestic ventilation systems draw air from the roof space, they are not directly drawing air from outside. Hence, they cannot be used to comply with the Building Code ventilation provisions.However, Building Code compliance is not generally an issue because domestic ventilation systems are installed in addition to opening windows.

Considerations

Installing domestic ventilation systems needs special care. The roof space must be clean and dry, as any animal waste, pathogens, allergens, mould and fungi in the roof space may be ventilated into the living space of the house. It is important to check for leaks in the roof space, as these may contribute to fungal and bacterial growth.