Steel Buildings in Europe

Part 8: Building Envelope 8 - 3 - Providing ventilation to a building (ventilated or unventilated roofs and walls). The cladding will also normally include ancillary components such as windows, rooflights, vents and gutters. As an alternative to the layout shown in Figure 1.1, some types of cladding may be installed directly to the primary steelwork without the need for purlins or cladding rails. Examples of this type of construction are deck and membrane for roofs and liner trays for walls. Where such solutions are chosen, the cladding must be designed to: - Span directly between the rafters, roof beams or trusses. This is usually achieved by the use of deep profiled decks or trays, but where these are insufficient for the required span, intermediate supports in the form of secondary beams or hot-rolled purlins will need to be installed. - Restrain the primary steel members. Structural decks and liner trays, if fastened correctly, should be able to provide sufficient lateral restraint to the outer flange of the supporting rafter or column. This should allow the columns and rafters to be designed as fully restrained under gravity loads or positive wind pressure. However, additional restraining members will need to be included in the structure in order to provide intermediate restraint against wind suction (uplift on the roof). 1.2 The functions of building envelope All buildings, whatever their use, must provide a controlled internal environment that is protected from the variable and uncontrollable external climate. The nature of the internal environment will depend on the intended use of the building and this will naturally determine the requirements for the building envelope. Generating and maintaining a controlled internal environment is a complex process, requiring a combination of mechanical and electrical services to heat and/or cool the building and a well-designed building envelope to regulate the heat gain and loss. The design of the building envelope is an important factor in specifying the Mechanical and Electrical (M&E) plant and in determining the energy performance of the building. With pressure to reduce energy consumption now being placed on the construction industry across Europe, the building envelope has never before been under such close scrutiny. In addition to forming the building envelope, the roof and wall cladding may also have an important role to play in the structural performance of the building, by providing restraint to the secondary steelwork against lateral-torsional instability. Where such restraint is assumed (as is often the case in the purlin and side-rail manufacturers’ load/span tables), it is essential that the cladding is capable of providing this restraint in practice.