A window is an opening formed in a wall or roof primarily to admit daylight through some transparent or translucent material. Windows also serve an important function in providing controlled natural ventilation to buildings and make a major contribution to the visual appearance of buildings. As the window is part of the wall or roof envelope, it should serve to exclude wind and rain, and act as a barrier to excessive transfer of heat, sound and spread of fire in much the same way that the surrounding wall or roof does.

7.1 Functional requirements

The primary function of a window is to:

  • Admit daylight and provide a view

Additional performance requirements include:

  • Safety – comply with relevant health and safety legislation, including the Construction Design and Management (CDM) Regulations
  • Strength, stability and airtightness
  • Fire safety
  • Provision of ventilation
  • Resistance to the passage of heat
  • Resistance to the passage of sound
  • Safety
  • Security
  • Aesthetics
  • Durability and freedom from maintenance

The key elements of a window within a typical wall detail are shown in Figure 7.1.

Diagram of a typical double‐glazing window with arrows depicting cavity wall construction (partial fill cavity), edge sealing/cavity closer (reduce thermal bridge at head), window head, window frame, etc.

Figure 7.1 Typical double‐glazing window detail.

Source: Adapted from Gorse and Thomas, 2013.


The prime function of a window is to admit adequate daylight for the efficient performance of daytime activities. The quantity of light admitted depends in general terms on the size of ...

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