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?

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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.  

Structural glazing diagram

Enlightening Window 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.

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  

Sika - Bonding Special Agents

Window bonding is carried out at the window manufacturer using specialist equipment. With a complete product portfolio for window installation and adhesives for window manufacturing, Sika contributes to the global drive for energy-saving buildings. Its window installation materials help meet the latest construction requirements, thus protecting the environment. Sika sealants, membranes and expansion tapes seal window frames to achieve air-proof building envelopes and protect the insulation from water infiltration, reducing heating or cooling energy output.

During the past decade, architects have increasingly looked to bonded windows to provide a stylish, cost-effective alternative to traditional sash-heavy installations. Whatever the bonded window application, Sika has the product range to provide a quality seal.