Speed of wind creates considerable forces on both top and bottom sides of the Roof Cladding and hence one must consider wind speed and its resultant forces while designing and installing a roof. Whilst the forces acting inward through the topside of the roofing sheet tend to push the Roof Cladding downwards, the outward forces acting through the bottom side of the roofing sheet tend to lift the Roof Cladding from its frame. Outward forces could be generated by either negative wind pressures outside the building or positive wind pressure inside the building.
Outward forces acting on roofing sheets through bottom side are most common and these forces must be balanced by providing right spacing between the Purlins and by selection of right diameter, length and number of fasteners. In cyclonic areas, extra care must be taken in designing and installation of roofs by consulting architects or professional shed fabricators.