Bonded windows can have a significant influence on a building’s thermal performance. It’s a simple, yet inspired method of insulation with proven energy-saving credentials – but how does it work?

In bonded windows the glass holds the sash, the opposite methodology to traditional windows where the sash holds the glass. Bonded windows require less reinforcement, reducing the risk of cold-bridging as well as optimising a window’s design to improve its U-value in terms of heat loss.

By reducing the total frame aspect of a window, steel reinforcements can be avoided and bigger chambers – such as the chamber for the steel reinforcement – can be splinted in smaller ones. Also, the adhesive splits the space beneath the glass edge which reduces the convection.

Enlightening installation

A bonded window goes beyond the conventional function of a window, providing protection from the worst weather. It also allows more natural daylight into a building, due to the reduced framework required to hold it in place. Not only does this additional benefit count as a superb energy-saving feature, it improves the health and well-being of a building’s occupants.
Other structural window bonding benefits include:

  • Less material costs (up to 30%)
  • Automated glazing process
  • Almost maintenance-free windows
  • Improvement of thermal insulating values and solar heat gains
  • Fewer frames mean a bigger insulating glass unit (IGU) section. Ordinarily, a LOI-coated and Argon- filled IGU has a better U-value than steel reinforced PCV-frames. A window’s U-value is calculated thus:
    The addition of U-value glass; multiplied with the glass section; plus the U-value frame; multiplied with the frame section; plus PSI value multiplied by the IGU edge; divided by the total window section. More glass also means more solar gain. In shorthand, the equation reads like this:
    UW = (Uf * Af + Ug * Ag + Øg*lg) / AW
    But let’s not allow maths to cloud the evidence, which couldn’t be clearer – better-designed bonded windows lead to a 10% reduction in heat loss.

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