How to Use WindCode

WindCode calculates site wind speeds and design pressures for buildings in accordance with AS/NZS 1170.2:2021. The tool evaluates all 8 cardinal directions and determines the governing (critical) wind direction.

The fundamental equation the tool solves is:

Where each multiplier accounts for a different physical factor affecting the wind speed at your site. The tool then converts wind speed to dynamic pressure:

Start by typing the site address into the search bar. WindCode uses Google Maps to pinpoint the location and automatically determine several key inputs:

• Wind Region — the tool identifies the AS/NZS 1170.2 wind region (A1–A7, B1–B2, C, D) based on the site coordinates
• Terrain Category zones — colour-coded overlays at 250m, 500m, 750m, and 1000m rings around the site
• Topographic elevation profiles — fetched via Google Elevation API for all 8 directions, used to calculate M_t

Sample: Site located at Flinders Lane, Melbourne — pinpointed on satellite imagery

Enter the building’s physical dimensions. These are critical for calculating pressure coefficients and local pressure zones:

• Width (b) — the across-wind dimension (perpendicular to wind direction)
• Depth (d) — the along-wind dimension (parallel to wind direction)
• Height (h) — eave height or mean roof height above ground
• Roof Type — flat, monoslope, gable, or hip
• Roof Pitch — angle in degrees (0° for flat roofs)
• Orientation — the compass bearing of the building’s front face (use the interactive compass widget to set this)

Sample: 5.0m × 5.0m building, 10.0m tall, flat roof, oriented at 349°

Configure the design parameters that determine the regional wind speed and annual probability of exceedance:

• Wind Region — auto-detected from address, or select manually (A1–A7, B1–B2, C, D)
• Importance Level — IL1 (low), IL2 (normal residential/commercial), IL3 (high consequence), IL4 (post-disaster)
• Design Working Life — typically 50 years for permanent structures
• APE (Annual Probability of Exceedance) — derived from Importance Level and Design Working Life. ULS = 1/500 and SLS = 1/25 for typical IL2 buildings

Sample: Region A2, Importance Level 2, 50-year design life — ULS APE 1/500, SLS APE 1/25

The regional wind speed V_R is looked up from Table 3.1 based on the wind region and APE. For example, Region A2 with 1/500 APE gives V_R = 45.0 m/s (ULS).

WindCode calculates the site wind speed by applying five multipliers to the regional wind speed. Each multiplier accounts for a distinct physical effect on the wind. Here’s what each one means:

ULS wind speed table — showing M_d, V_R×M_d, M_z,cat, M_s, M_t for all 8 directions. The governing direction (SE) is highlighted in bold.

SLS wind speed table — same multipliers applied with the serviceability APE (1/25). Lower wind speeds used for deflection and movement checks.

Terrain category is one of the most impactful multipliers. It classifies the ground roughness surrounding the site, which determines how much the wind is slowed by surface friction:

• TC 1 — Open water, mud flats (highest wind speeds)
• TC 2 — Open terrain, grassland, few scattered obstructions
• TC 2.5 — Suburban fringe, developing areas
• TC 3 — Suburban terrain, numerous close obstructions (most common for residential)
• TC 3.5 — Dense suburban, light industrial
• TC 4 — City centres, dense urban with tall buildings (lowest wind speeds)

When a site address is entered, WindCode displays terrain category zone overlays on the satellite map at 250m, 500m, 750m, and 1000m distance rings. You can click each zone per direction to set the terrain category at each distance, and the tool blends them into the effective M_z,cat per Section 4.2.

Terrain category zones for each direction at 4 distance bands, with colour-coded satellite overlay — green (TC4/city) through red (TC2/open)

Wind accelerates over hills, ridges, and escarpments. The topographic multiplier M_t captures this effect per Section 4.4 of the standard.

When a site address is entered, WindCode automatically fetches elevation profiles from Google Elevation API along 8 cardinal directions (±5 km from the site). It then analyses each profile to determine:

• Feature type — hill, ridge, or escarpment (or flat)
• H — height of the feature (m)
• L_u — upwind slope length (m)
• x — distance from crest to site (m)
• Slope — average slope (H / 2L_u)
• M_h — hill-shape multiplier per Table 4.4

The governing (maximum) M_t from all directions is used. For flat terrain, M_t = 1.0.

Elevation profiles for 6 directions showing the terrain features, crest points, and calculated M_h values. Flat terrain in this example gives M_t = 1.0 for all directions.

Once the wind speeds are determined, WindCode calculates pressure coefficients per Section 5 of the standard. These depend on the building geometry ratios:

Key ratios: h/d, d/b, the local dimension 'a', and action coefficients Kc,e, Kc,i, Ka

External Pressure Coefficients (C_p,e)

These describe how wind pressure is distributed across the building surfaces:

• Windward wall — positive pressure (wind pushing inward), from Table 5.2(A)
• Leeward wall — negative pressure (suction), from Table 5.2(B)
• Side walls — negative pressure (suction), from Table 5.2(C)
• Roof — varies by zone, roof type, and pitch, from Tables 5.3

Wall C_p,e values: windward +0.73, leeward -0.50, side walls -0.65

Internal Pressure Coefficients (C_p,i)

WindCode evaluates both internal pressure cases: +0.2 (positive internal pressure from open windward wall) and −0.3 (negative internal pressure from open leeward wall). Both cases are checked for the worst-case net pressure on each surface.

For each of the 8 wind directions, WindCode calculates the net design pressure on every wall surface, including edge and corner zones with local pressure factors (K_l):

• Front (Windward) — general area, K_l = 0.9
• Back (Leeward) — general area, K_l = 0.9
• Side wall (worst zone) — general area, K_l = 0.9
• Windward wall edge (0–a) — within distance ‘a’ from edge, K_l = 1.5
• Side wall edge (0–a) — within distance ‘a’ from edge, K_l = 1.5
• Side wall corner (0–a/2) — within distance ‘a/2’ from corner, K_l = 2.0

The local dimension is calculated as: a = min(0.2b, 0.2d, h)

Wall pressures (ULS) for North wind — showing C_p,e, C_p,i, K_l, q_z, external pressure p_e, and net pressure p_net for each surface zone

Roof pressures are calculated for each wind direction with zone-dependent coefficients that account for flow separation and vortex effects:

• Upwind (0–h) — region from windward edge to distance h
• Upwind (h–2h) — region from h to 2h from windward edge
• Upwind (2h–3h) — region beyond 2h
• Downwind — remainder of roof past the upwind zones
• Roof edge (0–a) — edge zone, K_l = 1.5
• Roof corner (0–a/2) — corner zone, K_l = 2.0 to 3.0 (most severe suction)

Roof pressures (ULS) for North wind — showing all roof zones with their K_l factors and net pressures

The summary section consolidates all results into the key governing values you need for design:

Summary output — critical direction (SE), max V_sit, and governing wall & roof pressures for ULS and SLS

Key outputs include:

• Critical direction — the wind direction that produces the highest pressures
• Max V_sit (ULS) — the governing site wind speed
• a dimension — the local pressure zone dimension
• Max +ve ULS wall pressure — maximum inward (positive) pressure on walls
• Max −ve ULS wall pressure — maximum suction (negative) pressure on walls
• Max local ULS (with K_l) — maximum pressure including edge/corner factors
• Max −ve ULS roof pressure — maximum roof suction
• SLS equivalents — serviceability pressures for deflection checks

Click Download PDF Report to generate a comprehensive multi-page PDF with all input parameters, multiplier tables, pressure calculations for all 8 directions, terrain category map, topographic profiles, and the summary. Ready to drop into your project files.