G4/AS1: Ventilation

G4 VENTILATION ACCEPTABLE SOLUTION G4/AS1 Spaces within buildings Part 2. Spaces within buildings 2.1 Ventilation of spaces within buildings 2.1.1 Overview 2.1.1.1 Ventilation of spaces within buildings is required to maintain air purity by a flow of outdoor air through the building envelope, with or without mechanical assistance. COMMENT: If activities or environmental conditions adjacent to external natural ventilation openings produce air pollution in any of the forms listed in Building Code clause G4.3.3 (refer to Paragraph 1.1.3.1(c)), it may be necessary to relocate the openings or use mechanical ventilation. 2.1.1.2 Ventilation of spaces within buildings must be provided by a) natural ventilation in accordance with Section 2.2; or b) mechanical ventilation in accordance with Section 2.3; or c) a combination of mechanical and natural ventilation in accordance with Section 2.4. 2.1.1.3 Kitchens, bathrooms, toilets and laundries that do not have an external wall must be mechanically ventilated in accordance with Section 2.3 or Section 2.4. 2.1.1.4 Buildings containing Type 5 fire alarm systems must have mechanical extract ventilation installed in kitchens. COMMENT: Refer to Acceptable Solution C/AS1 and Acceptable Solution C/AS2 for information on Type 5 fire alarms. 2.2 Natural ventilation 2.2.1 Openings 2.2.1.1 Where natural ventilation is available via adjacent spaces, specific ventilation is not required to small spaces such as hallways and lobbies in household units. 2.2.1.2 Natural ventilation of occupied spaces must be achieved by providing a net openable area of windows or other openings to the outside of no less than 5% of the floor area. The 5% floor area requirement does not apply to: Com Ind a) occupied spaces in commercial and industrial buildings where products listed in Building Code clause G4.3.3 are generated (refer to Paragraph 1.1.3.1(c)), as mechanical ventilation of these spaces is required; and b) household units and accommodation units where there is only one external wall with opening windows (refer to Subsection 2.2.2 for additional requirements if natural ventilation is used). COMMENT: 1. The net openable area of windows or doors is measured on the face dimensions of the building element concerned. 2. Fixing in an open position of doors and windows used for ventilation is necessary to avoid injury or damage from sudden closure in the event of strong winds or other forces. 3. Keeping water from entering the building must be considered for compliance with Building Code clause E2 External Moisture. MINISTRY OF BUSINESS, INNOVATION AND EMPLOYMENT 28 JULY 2025 Page 8