Winds create considerable forces on both the topside and the underside of roof cladding, and you must consider these forces in the design and fixing of any roof. The forces are:
- Inward forces tending to collapse the roof cladding inwards, caused by wind acting directly on the windward side, and;
- Outward forces tending to lift the roof cladding from its framing, and the entire roof structure from the rest of the building. Outward forces can be caused both by uplift from negative wind pressure outside the building, and by positive wind pressure inside the building.
Generally, the greatest wind forces imposed on roofs are due to outward forces. Because the dead weight of roofing materials is relatively small, the outward forces must be resisted by the roofing fasteners.
It is very important that the battens and roof framing are adequately fixed to the rafters and walls, and that under extreme conditions the wall framing is anchored to the footings. Special anchoring provisions may apply in cyclonic areas – please contact us in these circumstances.