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Wind Uplift Resistance
At the earliest possible stage, the wind load acting on the roof should be calculated as recommended in BS 6399 : Part 2 1997 ‘Code of practice for wind loads’.
Calculation should be based upon building height, site elevation above sea level, site topography, distance from hills and urban areas, building design life and roof design. Separate calculations for different wind directions may be necessary.
The effect of openings in the building, such as warehouse doors, must also be considered. The roof and membrane attachment design will respond to this design load with appropriate safety factors. Once design wind load has been established, the attachment method for each impermeable layer in the roof system must be selected to exceed this load (see 3.14).
In designs with high wind load, supplementary mechanical fasteners may be required. Special
consideration of design against wind load should also be applied where a bitumen sheet vapour control
layer is bonded to the crowns of a metal deck in an adhered design.
It has been established from experience and confirmed in relevant British
and Industry
standards that a partial bond of bitumen, applied consistently, can resist a maximum design load of
2.4kN.m-2. The equivalent for a full bond is taken as 3.6kN.m-2. However, caution must be
applied where a nominally full bond is used to secure a semi-rigid sheet, such as an insulation board,
because a full bond is rarely achievable in practice.
© 2006 Sarnafil Ltd. Legal Disclaimer
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