How wind loads a scaffold
An open scaffold is mostly empty space: wind passes between its tubes and boards and pushes on each member only a little. Even so, the combined force on a tall scaffold is significant, and it is one of the loads the design and the ties are there to resist.
Wind also acts on everything else on the scaffold. Loose boards can lift, stacked material can shift, and anything with a flat face — a sign, a sheet, a panel — catches far more wind than the tubes around it.
Exposure matters as much as wind speed. A scaffold on a tall building, at a corner, on open ground or near the coast sees stronger and gustier conditions than one sheltered by surrounding buildings.
Sheeting, netting and hoardings
Covering a scaffold with sheeting or debris netting changes it from a frame the wind passes through into a surface the wind pushes against. The force on the scaffold and its ties rises considerably.
Hoardings work the same way: a line of panels fixed to a scaffold frame is, in effect, a wall standing in the wind, and its frame, bracing and base are designed for that.
So sheeting, netting, hoarding panels and large signs are added only where the design allows for them. Adding them to a scaffold that was designed open is a change that needs the designer's agreement and, usually, more ties.
Ties and design for wind
The scaffold design takes account of the expected wind for the site and the height, and of anything attached to the scaffold. The result shows up mainly in the tie pattern and the bracing, and in how a hoarding or freestanding structure is anchored or ballasted.
Freestanding structures — towers, hoardings without a building to tie to — depend on their base, bracing and any outriggers, stabilisers or ballast specified, because there is no building holding them up.
The design is only as good as its installation. Every tie and brace the drawing shows has to be in place for the scaffold to perform as designed in wind.
When the wind rises
Sites agree in advance what happens as wind picks up: who decides to stop work, what is secured, and what is brought down. Waiting until the wind is strong leaves people doing the securing in the worst conditions.
Loose material, offcuts and tools are cleared or tied down; boards are checked to be secured; sheeting and netting are checked for tears and loose fixings. Work at exposed edges, and anything involving large panels, stops first.
Mobile towers are a particular concern: they are not left standing at height in rising wind without the measures their instructions require, and are not moved in wind.
Inspection after high wind
After high wind, a scaffold is inspected before anyone returns to it. The inspection looks at ties, bracing, boards, sheeting, netting and anything else attached, and at the base for signs of movement.
Damage is put right and the scaffold re-inspected before it is used again. If the inspection finds the scaffold has moved or a tie has failed, the scaffold is closed until the cause is understood.
Hoardings and sheeted scaffolds are designed for wind loading as a matter of course — a brief that states the location and the height lets the design account for it from the start.
