Floor Void Ventilation Requirements

The building regulations approved document c states suspended timber floors and suspended concrete floors including block and beam have a provision for ventilation on two opposing external walls of not less than 1500mm per metre run of external wall or 500mm per metre of floor area whichever works out to give the greater amount of ventilation.

Floor void ventilation requirements.

Ventilation openings should be provided on at least two opposite sides. The recommended minimum area of ventilation required for under a suspended timber floor is 1500mm 2 for every metre of perimeter of the structure. Voids should be ventilated by openings providing not less than 1500mm 2 per metre run of external wall or 500mm 2 per m 2 of floor area whichever gives the greater opening area. The timloc vent units will achieve.

This requires a minimum of 3 500 mm2of net open area for every 1 m2of the house plan floor area. A suspended floor is a ground floor with a void underneath the structure. The new zealand building code clause e2 external moisture includes an acceptable solution e2 as1 for subfloor ventilation of suspended timber floors. A minimum ventilation void of 150mm should be provided below the underside of precast concrete and timber suspended floors.

On shrinkable soil where heave could take place a larger void is required to allow for movement according to the volume change potential. Additionally if the span is greater than 10m the overall ventilation area should be increased to at least 0 6 of the total roof area. And the floor level of the garage is below the level of the building use the garage floor as the lowest floor for rating. Duo pitch roofs greater than 200 pitch or greater than 10m span should have additional ventilation at the ridge to assist airflow through the roof void equivalent to at least a 3 mm wide continuous gap.

However the floor structure is supported by external and internal walls. Where the exterior ground level is too high to carry air to the sub floor void in a straight line a telescopic underfloor vent should be attached to the back of the air brick to conduct and protect the airflow across up to 5 brick courses. Another common way these vents can be blocked is by an extension with a solid floor being built onto a property without providing proper access to the original vents. The floor can be formed in various ways using timber joists precast concrete panels block and beam system or cast in situ with reinforced concrete.

High volume change potential 150mm 300mm total void.