Steel Buildings in Europe

Part 8: Building Envelope 8 - 21 specified to meet the requirements for external envelope applications. Composite panels that use mineral wool fall in the same category. Factory insulated composite panels may use polyurethane (PUR) or polyisocyanurate (PIR). It is generally considered that PIR panels have improved performance in fire compared to PUR panels. The core of either type of panel is difficult to ignite. Panels with appropriate joint designs with either PUR or PIR filling do not present an undue fire risk, and PUR panels are the standard core in many European countries. Polystyrene filled panels present a fire risk, and their use is diminishing. 3.7 Durability All cladding systems suffer a certain degree of degradation over time due to moisture, atmospheric pollution and UV radiation. However, the cladding specifier can have a considerable influence on the long term performance of the cladding through careful selection of materials and good detailing. Once in service, regular maintenance will prolong the life of the building envelope. The metal from which the weather sheet is made is available with several types of coating with a wide variety of colours and finishes. Guidance on the expected design lives of these coatings is available from MCRMA Technical paper No. 6 Profiled metal roofing design guide [4] and also from ECCS-TC7 Publication 41 Good practice in steel cladding and roofing [6] . It is worth noting that the colour of the coating has a very significant impact on its design life. Light colours reflect thermal radiation more efficiently than dark colours, resulting in lower surface temperatures and a reduction in the degradation experienced by the coating. When detailing the building envelope, particular attention should be given to the avoidance of water and dirt traps by specifying suitable slopes and end laps. Careful detailing is needed at the external interfaces to avoid the ingress of water and at the internal interfaces to prevent water vapour from within the building entering the cladding assembly (resulting in interstitial condensation). In order to ensure that the building envelope remains fully functional throughout its design life, it is important that it receives regular maintenance, including inspection, removal of debris, cleaning and repair of damage. Since maintenance usually involves access by workmen, often carrying equipment, it is essential that this is allowed for in the design of the building envelope and the supporting structure. The need for maintenance may be greatly reduced by specifying a coating for the weathersheet with a ‘maintenance free’ guarantee for the expected design life of the cladding (typically 20 to 30 years). Such coatings can provide significant benefits to the client in terms of whole life costs and improved safety. 3.8 Structural performance Metal cladding systems are required to carry externally applied loads, such as snow and wind loading without deflecting excessively or compromising the other performance requirements. The individual characteristic loads (actions)