Glass Curtain Walling Systems

When assessing and addressing the vulnerability of windows, CPNI divides the problem and consequently our guidance, into two broad categories:

  • Punched window systems, which are ‘stand-alone’ windows incorporated into the façade of a building. Typically, each individual window comes with its own frame, which is mounted into the façade.
  • Glass curtain walling systems, which consist of a ‘wall’ of glass supported by a purpose designed structure, often made from aluminium. The glass curtain walling system typically spans between floors, giving the external appearance that the building is made entirely from glass.

The security properties of each of these types can be very different. This page contains information relating only to glass curtain walling systems. Information on punched windows can be found on the Window and Window Protection Systems page.

Features of Glass Curtain Walling Systems

The elements impacting the security resistance of a glass curtain walling system are:

  • The overall size of the window (this can impact on its blast resistance; bigger panes generally perform less well than smaller windows)
  • The type and thickness of the glass used and whether or not it is a double or triple glazed (laminated glass is preferred for security applications)
  • The type and thickness of any infill panels used in place of the glass, typically to cover services or areas where transparency is not required or desirable
  • The supporting structure for the glass/panels, often referred to as transoms (horizontal members/supports) and mullions (vertical elements). This includes the geometric shape, thickness, material, joint connections and fixings of the framing system.
  • The ‘bite’ of the glass (the ‘bearing area’ of the glass onto the framing system)
  • The fixing/anchorage of the glass to the frame (e.g. structural silicon) 
  • Openable windows/fixings and locking systems (if installed)

Glass curtain walling systems are generally highly sophisticated pieces of engineering. However, they can be classified into two broad types according to their method of fabrication and installation:

  • Stick systems. These systems are brought to site and installed in component form, piece by piece. In security terms, these systems are generally mass produced, are lower cost and their security performance is often lower than that provided by purpose designed unitised systems.
  • Unitised systems. These systems are assembled and glazed in the factory, transported to site and then installed onto the building. Often they are designed for a specific project and therefore there is greater scope to enhance the security performance of the systems.

Blast Resistance

CPNI is investigating and will shortly publish information relating to the blast performance of glass curtain walling systems. In the interim, guidance provided on the Windows and Window Protection Systems page should be considered.

Resistance to Ballistic Attack

It is possible to manufacture glass that is resistant to a range of ballistic threats. Each manufacturer will have their own design, but mainly they are based on multiple layers of glass that are laminated together. Some systems use polycarbonate or other types of material to work in conjunction with the glass to improve performance.

The manufacturers of glass curtain walling systems will often buy in bullet resistant glass from specialised suppliers. It is important therefore, that both the framing and the glass provide an appropriate level of protection.

Some types of bullet resistant glass may under certain environmental conditions, have a limited service life (discolouration and/or delamination may occur for example). A glass curtain wall manufacturer may advise against the use of certain types of bullet resistance glass, owing to the difficulty in replacing the glass during its life.

When procuring bullet resistant glass, it is very important to specify against a known standard and you should ensure that the manufacturer can provide you a test certificate demonstrating their compliance to the specified standard.

Further guidance on the ballistic resistance of glass is contained on the right and on the Protection Against Ballistic Attack page.

Resistance to Forced Entry

Windows are inherently vulnerable to forced entry and will therefore need to be supplemented with an additional barrier – commonly referred to as Window Protection Systems.

Window protection systems are designed for external or internal use on buildings. They provide protection against a range of forcible attack and a number of products have been tested and approved to CPNI levels using CPNI manual attack standards. Protection systems are divided into the following categories:

  • Bar sets
  • Internal security blinds
  • Internal security grilles
  • External window void protection

It is important to also consider the use of intruder detection systems, which can detect either an attempted or actual breach of a window. Further information is available from the links on this page.

If you are a client of CPNI and require assistance, please contact CPNI for advice. If you are not a client of CPNI please engage a reputable security specialist to help you.