Ventilated air space requirements for suspended timber floors

with a ventilated air space measuring at least 75 mm from the ground cover to the underside of any wall plates and at least 150 mm to the underside of the suspended timber floor (or insulation if provided). Two opposing external walls should have ventilation openings placed so that the ventilating air will have a free path between opposite sides and to all parts. The openings should be not less than either 1500 mm2/m run of external wall or 500 mm2/m2 of floor area, whichever gives the greater opening area. Any pipes needed to carry ventilating air should have a diameter of at least 100 mm. Ventilation openings should incorporate suitable grilles which prevent the entry of vermin to the subfloor but do not resist the air flow unduly. If floor levels need to be nearer to the ground to provide level access, subfloor ventilation may be provided through offset (periscope) ventilators;