Mounting structure calculation: what to consider to prevent accidents in strong winds

The mounting structure is the most neglected component and, paradoxically, the one that causes the most serious accidents. A module that comes loose 10 metres up is a risk to life and a direct civil liability for the installer. Structural design must take wind loads seriously — and in Brazil that means the NBR 6123 standard.

Wind does not push: it sucks

The classic mental error is to imagine the wind "pushing" the modules. On most roofs the dominant effect is suction (uplift): the wind passing over creates low pressure and tries to pull the assembly upwards, like an aircraft wing. Fixings must therefore resist mainly uplift, not just weight. NBR 6123 (Wind forces on buildings) is the reference standard for these calculations in Brazil.

What goes into the wind-load calculation

The main parameters are the region's basic wind speed (V₀), taken from the isopleth map in NBR 6123 (from about 30 to 50 m/s in Brazil); the S1, S2 and S3 factors (topography, roughness/height and statistical factor); and the pressure coefficients, which change with the roof zone. Edges and corners suffer far greater suction than the centre — that is where modules fly off first. The taller the building and the more exposed the terrain (coast, open country), the higher the load.

Good fixing practice

• Follow the fixing grid of the structure and module manufacturers (support points and distances defined in the manual — fixing outside them voids the mechanical warranty).
• Increase fixing density at edges and corners, where suction is critical.
• Use bolts and clamps at the correct torque and corrosion-resistant materials (stainless steel, aluminium), especially near the coast.
• On flat roofs with ballast, size the weight taking suction into account — simply resting the frame is not enough.
• Check the capacity of the roof itself (purlins, rafters): a strong structure is useless if the roof cannot hold it.

Where the wind attacks the roof most