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With modern non-traditional facades the link between appearance and form of construction is more flexible.  For instance, stone may be placed using traditional methods or may comprise thinner slabs bolted to a carrier frame.  Conversely metal panels may give a modern appearance to a traditional blockwork wall when they are used as overcladding.

It is common practice to think of design options in terms of materials, appearance and image, and indeed the client may well express preferences in terms of precedent buildings.  However, the constructor will be thinking in terms of function, buildability, safety, time and cost.

These latter aspects of the façade depend on the following primary decisions:

  • Should the façade be a heavyweight or lightweight construction?
  • What areas of glass should be used and in what orientation?
  • Should the façade be prefabricated or site-assembled?
  • Should the façade be a bespoke design or a standard system?
  • What are appropriate combinations of primary structure and façade?


Design guidance

CWCT has written a number of design guides as follows:


Bespoke or standard design:

Although two building envelopes are seldom the same they are equally unlikely to be entirely bespoke. Most building envelopes are constructed from systems of components. These offer benefits over bespoke design but are unable to deliver a completely unique construction. Some of the benefits to consider are:

Benefits of standard systems Benefits of bespoke design
  • Cost
  • Shorter design and manufacturing period
  • Familiarity of construction
  • Use of existing test results
  • Appearance
  • Greater structural capapabilities
  • More advanced shading devices
  • Standard system walls can be given a variety of styles by selecting appropriate infill panels and additional items such as brise soleil. It has to be remembered that even the most standard of systems will have bespoke components such as brackets, flashings, and interfaces with adjacent cladding. Modified standard systems are sometimes used. In these one or more of the framing profiles, such as a pressure cap, is changed but the structural and sealing components remain unchanged.

    Bespoke systems comprise framing components that are bespoke to a project. The profiles are designed and dies cut to extrude the required cross-sections. Note that bespoke wall may also comprise standard systems components were appropriate.


    Envelope types:

    Walls are constructed using on of the basic forms of construction shown below. Further information is available in CWCT Technical Notes:

    Stick construction
     
    Unitised construction
     
    This is the most common method of constructing curtain walls in the U.K. although it is less popular elsewhere.  Simiar techniques are used to assemble roof glazing.

    Stick construction consists of a grillage of mullions supported from the floor slabs and transoms.  These are assembled at site and the resulting openings are infilled with glazing or opaque panels.

    It has the advantage that it is economical and the construction sequence is flexible.  Disadvantages are the lengthy intallation time and high dependence on site workmanship to ensure acceptable quality.
     
     

    Unitised construction consists of pre-fabricated units normally the width of a glazing bay and one or two storeys in height.

    Units are supported from the edge of the floor slab.  Units are delivered to site glazed and infilled and only the unit perimeter seals are made at site.

    Unitised construction is marginally more expensive than stick construction but normally leads to a higher quality wall.  It should be noted that the choice of materials has a greater effect on cost.

    Unitised construction is quicker to install but requires better planning and larger lead times are required.
     
     

    Panellised construction
     
    Rainscreen
     
    Panellised construction comprises pre-fabricated panels that span from column to column. The panels are supported from the columns and not influenced by movement of the floor slabs.

    The panels require structural integrity to transfer the loads on them back to the columns. Either a precast concrete panel or a steel truss is used. Hence the North American term 'Truss wall'.

    Panellised wall can be installed more quickly than other forms of wall.
     
     

    Rainscreen is a plane of panels designed to protect the wall from rain. It may be constructed as overcladding supported on a brick or block wall or as an integral wall supported from mullions or studs spanning from floor to floor.

    Rainscreen overcladding is often used on refurbishment projects but may be used to advantage when constructing new buildings.

    Integral rainscreen walls supported from framing members are dependent on an inner air barrier to carry wind load and give the required air permeability.
     
     

    Structural glazing
     
    Structural silicone glazing
     

     

     
    Structural glazing comprises frameless glazing in which each glazing unit is supported by point fixings, normally bolted connections.

    The glazing units may be supported individually from a separate framed structure similar to that shown or a stick construction curtain wall. Walls of this type are frequently called 'Planar' walls although 'Planar' is a brand name and other products exist.

    In true structural glazing the glass components transfer load. It may comprise glazing units suspended one from another or glazing units supported from glass fins or portals.
     
     

    Structural sealant glazing is a method of bonding the glazing units to a frame. This has the advantage that the glazing appears from the outside to be frameless.

    In practice the glazing is bonded to a carrier frame that is bolted to a framing system such as that for a stick construction curtain wall.

    The glazing may be bonded on two edges (and framed on the other two) or it may be bonded on four edges. In the latter case small clips may be provided to provide mechanical retention.
     
     

    Insulated panels
     
    Built-up cladding
     

     

     
    Insulated panels comprise a a layer of insulation faced with metal or plastic sheets. The perimeter comprises a profile that enables them to interlock to provide a sealed structural connection.

    Insulated panels may be manufactured with windows installed but more normally windows are installed at site as the wall is assembled.

    Insulated panels have to be supported from a framework of columns and/or purlins. Profiles are often available to allow the use of different window systems as part of an insulated panel system.

    Built-up walls are constructed at site and comprise inner and outer skins with insulation and a structural frame between them. Windows and doors may be included in the construction.

    Profiled steel walls for industrial buildings are constructed in this way. Recently these construction techniques have been adopted for residential buildings and other materials have been used as the inner and outer skins.

    This method of construction may be used with a rainscreen outerlayer provided a cavity is included for drainage.

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