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Last edited 25 Feb 2021
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.
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.
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.
 Related articles on Designing Buildings Wiki
- BFRC window rating scheme.
- BREEAM Visual comfort Daylighting.
- BREEAM Visual comfort View out.
- Daylit space.
- Domestic windows.
- Double glazing.
- Double glazing v triple glazing.
- Glass manifestation.
- Glass mullion system.
- Low-E glass.
- Patent glazing.
- Rights to light.
- Secondary glazing.
- Stained glass.
- Structural glass assembly.
- Tempered glass.
- Triple glazing.
- Types of window.
- U value.
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