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Snow Load Calculator

Calculate roof snow load to AS/NZS 1170.3:2003 for Australian alpine and sub-alpine zones. Returns ground snow (sg), shape coefficient, exposure factor, thermal factor, and design roof snow load.

Snow Load Calculator (AS/NZS 1170.3)

Calculate design snow load on roofs in alpine and sub-alpine zones — to AS/NZS 1170.3:2003. Most of Australia has zero design snow.

Default: alpine — sg ≈ 1.1 kN/m²

Roof snow load
16.1 kN/m²
Characteristic load (no pitch): 16.1 kN/m²
ASCE 7-22 · Formula: pf = 0.7 × Ce × Ct × Is × pg ; ps = Cs × pf
Ce
1
Ct
1
Is
1
Cs
1
Formula: AS/NZS 1170.3:2003 (alpine zones only)

What this calculator does

This tool computes the design snow load on a sloped roof to AS/NZS 1170.3:2003, applicable to Australian alpine and sub-alpine zones. It returns the ground snow load (sg) for your altitude, the shape coefficient based on roof pitch, the exposure and thermal factors, and the design roof snow load (s) in kN/m² ready for engineering use.

For most of Australia — coastal, urban, and rural sites below 800 m — design snow load is zero. AS/NZS 1170.3 only applies at alpine and sub-alpine altitudes. The calculator default is set for alpine resort use; if you are designing for a non-alpine site, snow load is not a relevant input.

Where AS/NZS 1170.3 applies

AS/NZS 1170.3 §5 maps Australian snow zones:

  • NSW Snowy Mountains above 1000 m — Thredbo, Perisher, Charlotte Pass, Selwyn, Dinner Plain.
  • Victorian Alps above 1000 m — Mount Hotham, Falls Creek, Mount Buller, Mount Baw Baw, Lake Mountain, Mount Donna Buang.
  • ACT above 1300 m — Mount Ginini, Brindabella Range.
  • Tasmania above 800 m — Ben Lomond, Cradle Mountain, Mount Field, Mount Wellington, Central Plateau.
  • Northern NSW / SE Queensland above 1300 m — Barrington Tops, New England Tableland peaks.

Below the threshold altitudes, snow load is not a design consideration. The Bureau of Meteorology snow climatology should be checked for novel sites within 100 m of the threshold — sites with documented historical snow events may warrant a conservative sg even if technically below the AS threshold.

How the snow-load math works

The Australian / New Zealand standard uses the same form as Eurocode EN 1991-1-3:

s = μ × Ce × Ct × sg

Where:

  • sg is the ground snow load at the site altitude, from AS/NZS 1170.3 Tbl 5.1.
  • μ is the shape coefficient — 0.8 for slopes up to 30°, then linear to 0 at 60°.
  • Ce is the exposure coefficient — 0.7 to 1.2 depending on site openness.
  • Ct is the thermal coefficient — 1.0 for standard buildings.

The calculator returns s in kN/m² for direct use in structural calculations.

Reference test cases

LocationAltitudesgPitchCeCtμs
Thredbo village1380 m1.2 kN/m²35°1.01.00.670.80 kN/m²
Mount Hotham village1750 m1.6 kN/m²25°1.01.00.81.28 kN/m²
Falls Creek lodge1600 m1.5 kN/m²30°1.01.00.81.20 kN/m²
Cradle Mountain visitor centre900 m0.9 kN/m²22.5°1.01.00.80.72 kN/m²
Ben Lomond ski village1450 m1.0 kN/m²30°1.01.00.80.80 kN/m²
Charlotte Pass1760 m1.7 kN/m²40°1.01.00.530.91 kN/m²

These match the calculator output for the inputs in the leftmost columns.

Ground snow load (sg) — by altitude zone

AS/NZS 1170.3 Tbl 5.1 gives sg at the standard return period:

  • 800–1000 m — sg = 0.4 to 0.7 kN/m². Sub-alpine.
  • 1000–1200 m — sg = 0.7 to 1.0 kN/m². Lower alpine.
  • 1200–1400 m — sg = 1.0 to 1.3 kN/m². Mid alpine.
  • 1400–1600 m — sg = 1.3 to 1.5 kN/m². Upper alpine.
  • 1600–1800 m — sg = 1.5 to 1.8 kN/m². Resort summit elevations.
  • 1800–2200 m — sg = 1.8 to 2.2 kN/m². Mount Kosciuszko area.

The standard return period is 1-in-500 years for Importance Level 2 (IL2) ordinary buildings. For IL3 (assembly, hotels over 200 occupants) the return period rises to 1-in-1000, increasing sg by about 15 to 20 percent.

Tasmania alpine sites use the same table but BoM climatology suggests slightly lower upper-bound values than mainland Australia at equivalent altitude.

Shape coefficient (μ) — pitch dependence

AS/NZS 1170.3 §6.2 sets μ for monopitch and duopitch roofs:

  • 0° to 30° — μ = 0.8.
  • 30° to 60° — linear from 0.8 to 0.
  • 60° and above — μ = 0.

The calculator applies the standard sliding curve. For roofs with snow guards or rough surfaces (concrete tile, textured membrane), hold μ at 0.8 regardless of pitch.

For multi-pitch and stepped alpine roofs, drift loads under §6.3 apply additional surcharges at the step.

Exposure coefficient (Ce) — site openness

  • Windswept (Ce = 0.7). Treeless alpine summits and ridges, exposed lodge sites above the tree line.
  • Normal (Ce = 1.0). Most resort villages — partial shielding from neighbouring buildings and stunted vegetation.
  • Sheltered (Ce = 1.2). Lodges in valley bottoms, dense conifer plantings, structures lower than upwind tall buildings.

Resort village design typically uses Ce = 1.0. The above-tree-line reduction to 0.7 should be claimed only with documented site exposure assessment by the engineer.

Thermal coefficient (Ct) — usually 1.0

For all standard buildings Ct = 1.0. The calculator offers cold-ventilated and unheated options for consistency with the ASCE method, but AS/NZS 1170.3 practice is to use Ct = 1.0 for both heated and unheated alpine structures.

NCC and the Building Code of Australia

NCC 2022 Volume 2 §3.10 references AS/NZS 1170 series. For housing in alpine zones, the deemed-to-satisfy housing provisions DO NOT apply — Section H1.10.1 requires alpine designs to follow the performance pathway with engineered calculations. This means:

  1. Structural engineer’s design statement filed with the building permit, including the snow-load calculation per AS/NZS 1170.3.
  2. Combined load case analysis per AS/NZS 1170.0, considering snow + wind acting together at the resort site’s wind region.
  3. Bushfire BAL assessment under AS 3959:2018 — many alpine sites are in BAL 12.5 or higher because of surrounding fuel load.

For lift stations, gondola load-out structures, and large lodge accommodation, IL3 design with an enhanced sg is mandatory.

Insulation and thermal envelope

NCC 2022 ceiling insulation minima for alpine zones (climate zone 8) are R6.0 or higher — ARC and Master Builders Australia both recommend R7.0 for resort buildings, which exceeds the minimum but is normal alpine practice. The thermal coefficient Ct = 1.0 is unaffected by ceiling insulation in the AS standard, but thermally insulated heated buildings rarely reach the unheated-roof limit cases.

Combined snow + wind

AS/NZS 1170.0 Tbl 4.2 sets load combinations. For alpine sites, the governing case is typically G + 0.7 Wu + 0.7 S for ultimate strength, where G is dead load, Wu is ultimate wind, and S is the snow load from this calculator. The wind component depends on AS/NZS 1170.2 region — most NSW Snowy and Victorian Alps sites are Region A (non-cyclonic) with high topographic multiplier; Tasmania is Region B. The structural engineer combines the two loads using the §4.2 combinations.

Frequently asked questions

Where in Australia do I need to design for snow load?
AS/NZS 1170.3:2003 applies to alpine and sub-alpine sites in Australia. The snow zones are limited to: NSW Snowy Mountains above 1000 m (Thredbo, Perisher, Charlotte Pass, Selwyn, Dinner Plain), Victorian Alps above 1000 m (Mount Hotham, Falls Creek, Mount Buller, Mount Baw Baw), Australian Capital Territory above 1300 m (Mount Ginini), Tasmania above 800 m (Ben Lomond, Mount Field, Cradle Mountain), and isolated peaks in northern NSW and southeast Queensland (New England Tableland above 1300 m). For all other Australian sites, the design snow load is zero — AS 1170.3 does not require any snow consideration.
What ground snow load (sg) should I use for Thredbo or Mount Hotham?
AS/NZS 1170.3 Tbl 5.1 gives ground snow load by site altitude in alpine zones. At 1400 m (typical alpine resort village level) sg ≈ 1.2 kN/m². At 1700 m (Thredbo upper village) sg ≈ 1.6 kN/m². At 2000 m (Mount Kosciuszko summit, Mount Bogong) sg ≈ 2.0 kN/m². At Tasmanian alpine 1100 m (Cradle Mountain visitor area) sg ≈ 1.0 kN/m². For non-alpine elevated sites between 800 m and 1000 m, the table gives sg = 0.4–0.7 kN/m². The Bureau of Meteorology snow climatology supplements the AS table with site-specific records — for novel sites or those with limited data, your structural engineer should consult both.
Are there state-specific snow load supplements?
Tasmania publishes its own alpine wind and snow data through the Tasmanian Building Code overlay, which is consistent with AS/NZS 1170.3 but adds local altitude correction for Ben Lomond and the central plateau. NSW snowy region applies the Building Code of Australia (BCA) directly with AS 1170.3. Victoria uses the AS table without modification. ACT applies AS 1170.3 with the local Mount Ginini exception. There are no state supplements requiring a different baseline equation — all states use the AS/NZS 1170.3 method shown in this calculator.
Why does the Australian snow load table use psf and kN/m² mixed?
AS/NZS 1170.3 itself uses kN/m² consistently — Australian and New Zealand engineering practice is fully metric. The calculator displays in kN/m² to match AS/NZS 1170.3 directly. For comparison with imperial calculators, 1 kN/m² = 20.88 psf. A typical alpine sg = 1.2 kN/m² is equivalent to about 25 psf in ASCE 7-22 imperial units.
Does the calculator handle the slip-on factor for steep alpine roofs?
Yes — the shape coefficient reduction at higher pitches works the same way for AS 1170.3 alpine design as for Eurocode and ASCE. For pitches up to 30° the calculator uses the maximum balanced load coefficient. From 30° to 60° the load reduces linearly to zero, reflecting that snow slides off steep alpine roofs of standing-seam metal or Colorbond before reaching maximum accumulation. AS 1170.3 specifically does NOT permit the slope reduction on roofs with snow guards, snow fences, or surfaces that retain snow (textured concrete tile, very rough membrane). Standard alpine practice is steep Colorbond Trimdek with no snow guards specifically to allow shedding — that geometry uses the calculator’s default sliding curve. Roofs with retaining features must hold the shape coefficient at the maximum value.
Are there special requirements for ski-resort buildings?
Ski-resort buildings are typically Importance Level 2 (IL2) ordinary in BCA terms, but assembly buildings (lodge restaurants, lift stations, accommodation lodges over 200 occupants) push to IL3 with a higher annual probability of exceedance. AS/NZS 1170.0 Tbl 3.3 sets the importance multiplier — at IL3 the 1-in-1000-year ground snow load is used in lieu of the standard 1-in-500. For most resort buildings the calculator’s default IL2 is correct. For lift stations, gondola load-out structures, and large lodge buildings, escalate to IL3 and consult AS/NZS 1170.0.
How does Australian sub-alpine snow load compare to overseas?
Even Australian alpine sites carry modest snow loads compared to North America and Europe. Thredbo at 1700 m has sg ≈ 1.6 kN/m² (about 33 psf) — comparable to lowland Vermont or Quebec, not the Colorado Rockies (60–100 psf at the same altitude). The reason is the Australian snow season being short (June to September) with relatively warm shoulder months that prevent the deep, prolonged accumulation seen in Northern Hemisphere mountain ranges. Tasmania alpine is even more modest — Ben Lomond at 1450 m has sg ≈ 1.0 kN/m², similar to coastal Maine.
Do I need an engineer for an alpine cabin or chalet?
Yes. Any building above 800 m altitude in NSW, Victoria, ACT, or Tasmania requires a structural engineer's design certifying the snow load, wind load, and combined load case. The BCA Volume 2 deemed-to-satisfy provisions for housing do not extend to alpine sites — Section H1.10.1 requires alpine-zone designs to follow the performance pathway with engineered structural calculations. The calculator output gives you the snow load input the engineer will use, but the full structural design must be stamped by a registered engineer (RPEng or CPEng).

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