How are triple glazed windows manufactured

We have gradually come to a stage where double glazed windows are just not enough to keep up with the requirements of energy efficient homes. With the need for a cleaner, greener environment with reduced carbon footprints, triple glazed windows seem to perform the task optimally, efficiently and economically.

Building requirements in the UK require a window to have a U value of at least 1.6. A U-value is the rate of heat loss through a window. The lower the value, the more effectively the window can resist thermal heat loss.

Traditional single paned windows have a U value of more than 5. With the introduction of double glazing, windows performed with a U value of over 3 and now with triple glazing, U-values have dropped even further to less than 1. Today, installing triple glazed windows offer not just better U values, but also reduced energy bills and higher returns on the real estate front.

Every home is unique in its design and needs. While some opt for openable windows, fixed windows have proved to be more effective in keeping the cold out in winter and heat out in summer. For your new insulated window to perform optimally, you will also have to address the rest of the heat-loss areas of your home: walls, floors and ceilings all have a significant impact in how your home performs thermally.

Let’s first look at the make-up of a window frame

About 10 to 30% of a window opening is typically taken up by a window frame. The basic combination of frame and glass is the major contributor to the thermal performance of a window. It is essential to use the right material in making a window to optimize performance, lower maintenance and prolong its lifespan.

Design and manufacturing

An experienced window manufacturer is an essential requirement for designing windows that fit your needs, both financially and aesthetically. They take into consideration climatic conditions and their intended use – commercial and residential windows will have different requirements and specifications - to determine which materials are to be used for the frame, the most suitable glass, the ideal gas and related hardware and accessories.

Automated manufacturing systems ensure minimized human handling that can lead to fingerprints and other marks on the inside of the glass and frame. Computerized testing of all windows is carried out to ensure a high-quality product with reduced wastage of raw materials and easier diagnosis and solution of potential problems.

How is the sealed glass unit manufactured?

The required dimensions including the height, width and thickness of the window units are noted and fed into the automated systems of the assembly line. Based on the dimensions, spacers of specified thickness are cut, assembled and filled with a drying agent.

Adhesive sealants are applied on both faces of the spacers. The cut and washed glass panes are pressed against the spacers. The optimal thickness of the glass pane in a triple glazed window is 4mm and the optimal space between the glass panes, is 16mm. The gaps are filled with Krypton gas to create an optimal thermal barrier and is then sealed. Krypton gas, though slightly higher in cost, enables reduction of the cavity width and performs better than Argon-filled double glazed windows.

The edges are sealed with polysulfide or silicone sealant to prevent any entry of air inside the unit. The drying agent ensures removal of humidity from the gas-filled space so that condensation does not occur on the inside of the glass panes.


There are 3 different methods of introducing gas into the cavities


Assembling the window unit in a gas filled environment with a sealed assembly press.

The two glass panes are moved into place and the press is sealed. Krypton gas is pumped into the bottom of the unit as air escapes from the top, after which the completed unit is vacuum sealed.


Placing the assembled unit in a chamber from which all the air is extracted by creating a vacuum.

Krypton gas is then replaced in the chamber, which consequently enters the cavity in the window.


One or more lances (metal pipes for supplying jets of air or gas) are inserted into the holes in the glass cavity.

In this two-hole filling method, air is exchanged with Krypton gas from the bottom lance, as air escapes from the top lance.

Introducing the gas fill in a controlled environment like a vacuum, ensures that there is complete removal of air from the cavity.

Frames play a major role in improving the overall energy performance of a window. The three commonly used framing materials are wood, PVC and aluminum. The glass panes never touch the frame, but are set on small blocks within the frame and are held in place with caulking or gaskets.


There are 3 different methods of testing the quality and performance of a triple glazed window:


Samples can be drawn from the insulating cavity and tested for residual oxygen with either an oxygen analyser or gas chromatograph.


With video thermography, thermal performance of the whole unit can be determined.


There are also handheld devices that can measure the concentration of gas in a window unit. It works simply by pushing the device against an insulated glass window and pressing a button. Instant results of the concentration of gas are obtained and can be easily stored and downloaded to a computer.

Installation of a triple glazed window

The installation process of a triple glazed window is as important as the manufacturing process. A poorly installed window will not operate as desired even though the window itself may be excellent in energy efficiency. You may end up spending more in repairs to seal cold drafts during winter and leakages during rainy season. It is therefore advisable to employ knowledgeable and professional window installers who also provide a warranty on their products.

Some basic notes to be kept in mind while inspecting windows after installation:

1.    The installation should be insulated and air tight without any gaps between the wall and the frame.

2.    The window should be level and straight. Use a spirit level to check if you’re unsure.

3.    The area around the frame should be sealed with non-expanding foam before finishing and painting the surround. Especially where damage occurred to the surrounding wall structure, care should be taken to ensure proper insulation.


Energy rating of windows

Windows, glazed doors and skylights account for about 25% of heat loss in a home. Energy ratings are determined using computer software along with standard product testing procedures. The window energy rating (WER) system was set up by the British Fenestration Rating Council (BFRC) in 2004 as a way for windows to be rated according to one standardized system. Windows are rated on a scale of A-G, with A rating as the most efficient and G being the least. The rating applies to the entire window unit, including the frame and glass. Where double glazing has A ratings or, because of new technological developments in glass, A+ ratings, triple glazing has WER of A++. This results in a much more efficient window and a significant cost saving in annual heating bills.

While there are companies claiming that triple glazing can be retrofitted onto existing double glazing, the manufacturing process clearly does not support that notion. It’s not merely 3 panes of glass that make up a triple glazed window; it’s specialized glass, combined with 2 gas-filled cavities in a sealed frame that give superior insulating properties to triple glazing. It is almost impossible to incorporate the features of a high performance, energy efficient window that combines insulated glass, inert gas fills and low-e coatings inside a sealed frame, into an existing window frame. Upgrading your existing windows by adding a third layer of glass therefore is a temporary solution that will not give you the energy efficiency that you expect of triple glazing.

Published on : 20th February 2017

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