Last edited 25 Feb 2021

Single glazing

The term 'glazing' refers to the glass component of a building's facade or internal surfaces.

Historically, the external windows of buildings were generally single glazed, consisting of just one layer of glass, however, multi-layered glazing system were developed such as double glazing and triple glazing to improve performance.

Single glazing comprises off one layer of glass, bedded into the window frame. Single glazing is traditionally fixed with linseed oil putty and secured with glazing nails into the frame. Glazing beads can further secure the glass and are usually screwed and glued to the frame. If the window frame is timber it must be painted or otherwise treated to avoid water ingress.

Single glazing has poor thermal performance, and may not be permitted in new buildings other than those which do not have controlled internal environments, such as storage facilities.

U-values (sometimes referred to as heat transfer coefficients or thermal transmittances) are used to measure how effective elements of a building’s fabric are as insulators. That is, how effective they are at preventing heat from transmitting between the inside and the outside of a building. Typically, the U-value of single glazing is around 4.8 to 5.8 W/m²K, whilst double glazing is around 1.2 to 3.7 W/m²K. Triple can achieve a U-value of below 1 W/m²K.

Thermal performance is affected by the quality of the installation, the inclusion of thermal breaks in the frame, suitable weather seals, and the type of glass used. For example, low-e glass has a coating added to its surfaces to reduce its emissivity so that it reflects, rather than absorbs, a higher proportion of long-wave infra-red radiation.

The sound reduction achieved by single glazing (6 mm thick) is typically around 27 dB, whilst double glazing (with a 100 mm air space) is around 42 dB.

It should be noted that from 1st April 2020 it will be against Building Regulations to rent a property which breaches the minimum requirement of an E rating on an EPC certificate. Single glazing can have a big impact on the energy efficiency of a building and to comply with the regulations, single glazing might have to be adapted. Secondary glazing can be an option if double glazing can not be installed.