Steel Buildings in Europe

Part 8: Building Envelope 8 - 7 potential for air gaps between the insulation and the profiled metal sheets. Rigid mineral wool slabs are also much heavier than mineral wool quilts, with consequences for the loading on the supporting steelwork and manual handling on site. 2.2.3 Spacer system The primary function of the spacer system is to support the weather sheet at the required spacing from the liner sheet. The components of the system must, therefore, possess sufficient strength and stiffness to safely transmit the required loading through to the purlins, without excessive deformation. A common form of spacer is a bar and bracket system, as shown in Figure 2.5. The system consists of cold formed steel bars, which provide continuous support to the weather sheet, supported at intervals by steel brackets firmly attached to the purlins through the liner. Many bar and bracket systems also incorporate plastic pads (which act as thermal breaks) in order to minimise thermal bridging. Other types of spacer systems are also available, for example Z spacers supported on thermally insulating plastic blocks. 1 2 3 4 1 Bar 2 Bracket 3 Sway bracket 4 Purlin Figure 2.5 Bar and bracket spacer system 2.2.4 Weather sheet The outer sheet of a double skin built-up cladding system is known as the weather sheet. As the name suggests, its primary function is to protect the building from the exterior climate by forming a weather-tight envelope. However, the weather sheet should also be regarded as a structural element, as it plays an important role in transferring externally applied loads (e.g. from wind, snow and foot traffic) through to the other cladding components, secondary steelwork and the primary load-bearing frame. The weather sheets are usually made from either steel or aluminium and are available in a wide variety of finishes and colours. Steel weather sheets are manufactured from pre-coated steel coil. Aluminium weather sheets are available in a mill finish or in a range of painted finishes. Detailed requirements for the weather sheets for roof and wall cladding applications are given in EN 14782 [1] .