Wind load guidance for temporary site fencing

Temporary site fencing, including wire mesh panels, debris netting and solid hoarding, is exposed to wind throughout its deployment. Unlike permanent structures it is rarely anchored to the ground, so its stability depends almost entirely on the weight of the panel, the stabiliser feet, any added ballast, and the friction between those feet and the surface. Understanding how wind acts on a fence, and how that load is resisted, is essential for keeping sites safe and compliant.

How wind force is calculated

The wind force on a panel is found from the dynamic pressure of the moving air: F = ½·ρ·v²·Cf·A. Here ρ is the density of air (about 1.225 kg/m³ at sea level), v is the wind speed in metres per second, Cf is a force coefficient that depends on how porous the fence is, and A is the face area of the panel. A solid hoarding panel has a high Cf because it blocks all the air, while an open wire mesh panel has a much lower Cf because roughly half the air passes through. Debris netting fixed to mesh sits between the two, as the netting catches much of the flow that the mesh would otherwise let through.

Overturning and sliding

Wind pressure acts at the centroid of the panel, creating an overturning moment about the leeward edge of the stabiliser foot. This is resisted by the restoring moment from the self-weight of the panel, feet and ballast acting through their lever arms. The factor of safety against overturning is the restoring moment divided by the overturning moment. Sliding is simpler: the wind pushes the panel along the ground and is resisted by friction, equal to the coefficient of friction μ multiplied by the total normal weight W. The factor of safety against sliding is the friction resistance divided by the wind force.

Choosing a design wind speed

Wind speed varies across the UK and through the year. Coastal and northern towns such as Inverness, Aberdeen and Plymouth see higher annual mean speeds than inland cities, and winter is consistently the windiest season. A reasonable design approach is to take the annual mean for the nearest town and apply a seasonal multiplier, or to use a recognised gust value for exposed sites. The calculator includes representative UK town speeds and seasonal factors so a sensible value can be selected quickly, but local conditions, funnelling between buildings and forecast gusts should always be considered.

Improving stability

Where a configuration is marginal or unstable, stability can be improved by adding ballast to the feet, choosing a heavier foot type, selecting a less porous fence, or adding bracing. A short brace props under the rear edge of the foot and transfers upper wind load into a stabilising downforce. A long brace pegged into the ground behind the foot widens the effective base and anchors the upper portion of the load, improving both overturning and sliding resistance. Always confirm final arrangements on site with a qualified engineer before deployment.