Wall and roof cladding to withstand the forces
Ensuring that the wall and roof cladding of a building is able to withstand the forces which are likely to be applied to it during the building life, are essential to maintain the functional performance of the cladding.
Wind pressures can produce some of the largest and most variable forces and this need to be accurately calculated.
What are the current standards, which should be used to calculate wind loadings on a building?
The correct standard is BS EN 1991-1-4. This contains the National annex (for UK and Ireland) of the European standard. The British Standard BS 6399 was withdrawn on 31/03/2010 and is now no longer valid.
What factors influence the wind load on a building, and how will the load influence the cladding specification?
The wind load on a building can be influenced by its size, location, height above sea level, orientation to the prevailing wind, and local topography or land features. All of these factors influence the general and local loads on the building, and key design features at eaves, corners and parapets.
The wind loading can vary considerably and can change quickly from a positive load to a negative load on adjoining areas. The structural engineer calculates the wind load at the design stage but specific local loads can influence the choice of cladding sheet, purlin spacing, fastener and number of fasteners.
Our supply chain partners can provide guidance on these aspects of the specification through the use of detailed wind load calculation software based on BS EN 1991-1-4. This exclusive software package allows these cladding system manufacturers to optimise the cladding design and installation requirements.
How do I ensure the roof and wall cladding system that I specify is able to meet these requirements?
The cladding system manufacturer should be able to provide detailed load span tables for cladding. The load span tables are specific to the exact profile chosen and cannot be used generically.
All our supply chain partners are able to supply load span tables, which have been calculated in accordance with EC3, the European method for calculating structural performance. These have been independently checked by the Steel Construction Institute and carry the SCI Assessed mark.
The system manufacturer should also be able to demonstrate that the pre-finished steel used for the cladding, meets the gauge requirements of EN10143:2006. The usual gauge of material used for built-up roof and wall cladding is 0.7 mm and 0.5 mm respectively.
Using lighter gauge material will increase the risk of cladding failure due to excessive deflection or localised bucking of the profile.