AS/NZS 1170.3:2003 (R2016)
Structural Design Actions — Snow and Ice Actions
AS/NZS 1170.3:2003 (Reconfirmed 2016) specifies snow and ice actions for the design of buildings and other structures in Australia and New Zealand. It defines snow regions on a national map (areas above approximately 600 m elevation in Tasmania, the Australian Alps, Snowy Mountains, New England Tableland, and most of the Southern and Central New Zealand mountains), prescribes ground snow load values for the relevant return periods, gives roof snow load conversion factors based on roof pitch and exposure, and treats drift loading at parapets, valleys and adjacent-roof step-downs. The standard also covers ice loading for line structures (transmission lines, communication towers) and atmospheric ice accretion on building elements where relevant. AS/NZS 1170.3 is the deemed-to-satisfy reference for snow and ice actions under NCC Volume One and is applied alongside AS/NZS 1170.0 (combinations), AS 1170.1 (imposed) and AS 1170.2 (wind). For most of mainland Australia outside the alpine regions, the standard's snow load is zero, and the practical application is to elevated alpine assets, communication towers, and ski-resort infrastructure. The 2003 edition with 2016 reconfirmation remains current.
AS 1170.3 has limited but real application to TRSC's existing-asset practice. The standard governs three categories of asset where snow and ice actions are decision-controlling: alpine commercial buildings (lodges, ski-resort infrastructure, accommodation structures in elevated regions), communication and transmission infrastructure (towers, line systems exposed to ice accretion), and high-elevation industrial assets (mining, quarry and energy facilities above the 600 m threshold). TRSC's Queensland practice rarely engages with snow loading directly — the Queensland alpine zone is small, and the assets that fall into it are mostly remote infrastructure rather than commercial buildings — but engagements in the New England, Southern Highlands and Snowy Mountains regions do require the standard, particularly when the firm acts on behalf of NSW or Victorian asset owners with portfolio assets in elevated locations. Three application points matter when the standard does apply. First, the ground snow load is an input to the roof snow load via the conversion factor, and the conversion factor depends on roof pitch, exposure and the presence of obstructions (parapets, plant rooms, adjacent taller buildings). For low-pitch roofs (less than 15 degrees), the full ground snow load is typically assumed on the roof; for steeply pitched roofs (over 30 degrees), reductions are permitted reflecting natural snow shedding. Existing-asset assessment in alpine regions frequently encounters roofs that have been converted from steep traditional pitches to lower-pitch profiles during refurbishment — and the lower-pitch roof carries higher snow load than the original, which can render previously adequate roof framing inadequate. Second, drift loading at parapets and adjacent-roof step-downs is the most commonly under-applied provision. AS 1170.3 specifies drift-load triangular distributions at upwind parapet faces and at adjacent-roof step-downs, with peak values up to 3 to 4 times the ambient roof snow load. Existing alpine assets with refurbished plant rooms, added rooftop equipment, or vertical extensions frequently have drift-loaded zones that did not exist at original design and were not assessed in the as-installed roof framing. TRSC's approach for alpine portfolio assessments includes a dedicated drift-zone check at every step-down and parapet condition, with the AS 1170.3 drift profile applied to the as-installed roof system. Third, ice accretion loading is rarely decision-controlling for buildings but is critical for communication towers and other line structures. The standard's atmospheric icing factor depends on elevation and proximity to maritime fog conditions; for mainland Australia, ice accretion is typically not the controlling action, but communication towers in the New England Tableland and Snowy Mountains do carry significant ice loads that must be combined with wind action per AS 1170.0.
Form 15 RPEQ certifications for alpine and elevated assets reference AS/NZS 1170.3:2003 as the snow-loading basis where the asset falls within the standard's snow region. For most TRSC engagements (Queensland, coastal NSW, coastal Victoria, NT, WA), AS 1170.3 does not contribute to the Form 15 governing combination. For alpine and elevated assets, the Form 15 file retains the AS 1170.3 ground snow load value, the roof snow load conversion factor, the drift-zone analysis at every parapet and adjacent-roof step-down, and the ice accretion analysis where applicable. The Form 15 explicitly states whether snow loading was checked and the basis on which it was either applied or excluded — engineers cannot assume snow loading is irrelevant without documenting why.