Wind Loads (AS/NZS 1170.2:2011)

How it calculates

The Wind Loads (AS/NZS 1170.2:2011) calculator determines site wind speeds and design wind pressures for rectangular enclosed buildings per AS/NZS 1170.2:2011 (Amdt 5). Wind is evaluated in all eight cardinal and ordinal directions, with terrain, topographic, shielding, and directionality multipliers applied independently per direction or as a single worst-case value.

Regional and site wind speed

The regional wind speed V_R is looked up from the wind region map for the chosen return period and importance level. The design site wind speed in each direction (V_sit,beta) is then:

V_sit,beta = V_R × M_d × max(M_z,cat × M_s, M_t)

Where:

• M_d - wind directionality multiplier (default 0.95 for structural)
• M_z,cat - terrain/height multiplier, interpolated from AS/NZS 1170.2:2011 tables for terrain category and height (TC1 through TC4, evaluated at 10 m height intervals)
• M_s - shielding multiplier (accounts for upwind shielding buildings)
• M_t - topographic multiplier for hills, ridges, or escarpments

The maximum site wind speed across all eight directions, V_h, is the governing design wind speed. The calculator also reports the equivalent AS4055 wind class.

Design wind pressures

Velocity pressure at height h is derived from the design site wind speed. External pressure coefficients (C_pe) are applied to each building surface - windward wall, leeward wall, side walls, roof zones - per AS/NZS 1170.2:2011 Cl. 5. Internal pressure coefficients (C_pi) depend on the enclosure condition: the calculator evaluates the dominant opening ratio to classify the building as enclosed, partially enclosed, or open.

Net design wind pressure on each surface combines external and internal components:

p = q_des × (C_pe - C_pi)

Outputs

The calculator reports V_R, V_h, the equivalent AS4055 wind class, and a load table of net wind pressures for each wall and roof zone in all relevant directions. A separate serviceability wind speed and pressures are also computed for deflection checks. All results are shown with their governing AS/NZS 1170.2:2011 clause references, and the load table can be linked to any ClearCalcs design calculator.

Assumptions and scope

The calculator assumes a rectangular enclosed building per Cl. 5, flat suburban terrain by default. Lee wind effects and special K factors are entered manually where required. A positive wind pressure acts toward the surface. Note: the Climate Change Multiplier introduced in the 2021 edition is not present in this 2011 calculator.