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How to use the wind load calculator

From the basic wind speed to the pressure on every wall and roof zone: what each input means, which table to use for the frame and which for the cladding.

All guides Inputs Result Calc sheet Walk-through Mistakes

1. What the calculator does

The wind load calculator works out the wind pressures on a rectangular building with a duo-pitch, mono-pitch or hipped roof. From the basic wind speed, the terrain and the height it finds the peak velocity pressure q_p; then it applies the pressure coefficients for each wall and roof zone, for both wind directions, with the internal pressure. It gives the overall wind force for the frame and bracing, the local peak pressures for cladding and fixings, and a pressure schedule for all buildings in the project.

The code routes are SANS 10160-3 and EN 1991-1-4. The roof options name the code tables they use.

Wind load calculator header — The header. The summary shows q_p and the governing net pressure.

2. The inputs, group by group

Input	What it means	Typical value
Building	A name and the design code.	B1, SANS 10160-3
Wind	Basic wind speed v_b for the site, terrain category (A sea / open water, B open flat country, C suburban / woodland, D urban / dense) and site altitude above sea level.	v_b 32 to 44 m/s, terrain C
Size	Breadth b across the wind, depth d along the wind, eaves height and which height the code uses (eaves, or eaves + rise).	28 × 12 m, eaves 10 m
Roof	Duo-pitch, mono-pitch or hipped, and the pitch α.	Duo-pitch, 15°
More inputs	Internal pressure from openings, canopies, the dominant face and other options.	default c_pi +0.2 / −0.3

Wind load inputs: building, wind, size and roof — The inputs. Breadth is across the wind and depth along it; the calculator checks both wind directions for you.

3. How to read the result

The building sketch shows the net pressures on each face for the governing case. The loads card gives q_p, the method checks and the overall wind force on the building for each direction, split into walls, roof and friction: these are the forces for the frame, bracing and foundations.

Building sketch with the wind pressures on each face — The building sketch: q_p = 0.47 kPa, and the net pressures on the windward wall, leeward wall and roof.

Wind loads card with method checks and the overall wind force — Method checks (11 of 11 apply, governing net 0.70 kPa in zone F) and the overall wind force on the building.

The zone table lists every wall and roof zone with its pressure for wind at 0° and 90°, and the governing value. Use these for the purlins, girts and rafters. The local peak table gives the pressures on a small loaded area (1 m²) for cladding and fixings: higher than the zone values, especially at the roof edges and corners.

Zone pressure table for both wind directions — Zone pressures for both wind directions, with the governing value and the direction it comes from.

Local peak pressures and internal pressure from openings — Local peak pressures for cladding and fixings, and the internal pressure from openings.

The governing line is the largest net pressure, here −0.70 kPa (suction) in roof zone F with the wind at 90°. Anything the engine cannot work out for your building shows as NOT CHECKED: check it by hand or with the code tables.

4. Calc sheet and schedule

The result (pass / fail and utilisation) stays free for everyone. Every check with its clause, the calc sheet and the bending schedule are open to signed-in users. Sign in free: 3 designs a month (one calculator, open for 24 hours). Unlimited with a calculator pack.

The full detail drawings are part of the paid plan. The combined pressure schedule collects the zone pressures of all buildings in the project in one table.

Combined pressure schedule for all buildings — The combined pressure schedule: every zone of every building, with q_p and the net pressure.

5. A 2-minute walk-through

Open the calculator: a 28 × 12 m building, eaves 10 m, duo-pitch 15°, v_b 32 m/s, terrain C.
Read q_p (0.47 kPa) and the governing net pressure (−0.70 kPa, zone F).
Change the terrain to B (open country) and watch q_p and every zone pressure go up.
Change the roof pitch and see how the roof zone pressures change.
Copy the overall force to your frame design and the zone pressures to the purlins.

6. Common mistakes

The wrong basic wind speed. Take v_b from the map for the site, not a round number.
Terrain too rough. Terrain D lowers the pressure; use it only where dense buildings surround the site on all sides and will stay there.
Zone pressures for cladding. Cladding and fixings take the local peak (1 m²) values, not the zone values.
Internal pressure left at the default for a building with a large dominant opening, such as a roller door that can stay open in a storm.
Characteristic and design mixed up. The pressures are characteristic; the load factor comes in the combination.

7. Where it fits

The pressures go to the portal frame, purlin and girt, and masonry wall calculators.

8. Learn more

Try it nowThe calculator opens with the walk-through inputs above. The result is free; sign in for the checks, calc sheet and schedule.
Open the wind load calculator

A guide to using the calculator, not a design. Check every value against the current code and your own project, and have the design checked and signed by a registered professional engineer.

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