A triple glazing unit

Triple glazing: is it worth it?

As UK households face the prospect of escalating energy costs, this article examines whether triple glazing is a viable way to make a house warmer and reduce heating bills; it investigates the concept, assesses the pros and cons and looks at energy performance before reaching a conclusion.

Dive in to find out all the facts about triple glazing!

Cross section of a triple glazed window unit.

What is triple glazing?

Triple glazed window units comprise a sealed frame containing three panes of glass which create two airlocks; the glazed cavities are filled with an insulator such as argon gas or krypton gas. Compared to double glazed windows, triple glazing has a lower `u’ value (the measurement used to compare the thermal performance of windows); lower `u’ rates mean better insulation. Thermal efficiency can be improved by variables such as the type of air or gas used, installing warm-edge spacer bars around the frame perimeter and using different coatings on glass or low emissivity glass to reduce energy loss from the inside.

The actual frame is an important consideration regarding efficiency as well as the panes of glass; airtight insulated frames work best. Although upvc is commonly used in triple glazing frames, it is a poor insulator; timber-framed and aluminium units give the best results, but they are more costly.

To date, uptake of triple glazing is small in the UK, however, it is widespread in cold climate countries such as Scandinavia where it is standard in most houses. It is important to be aware that double or triple glazing only works well in a house which is properly insulated in terms of its walls, door, roof and floor; the standard of glazing must match the level of insulation for warmth consistency around a house.

The benefits of triple glazing:

  • Having triple glazing installed improves the thermal potential of windows, reducing heat loss which can lead to lower energy bills.
  • Triple glazed windows make a home warm by trapping heat; thermally efficient windows increase internal air temperature.
  • Security is improved as triple glazed windows are stronger than double glazed units.
  • The third pane of glass enables significant noise reduction; however, if sound insulation is a priority, secondary glazing may well be a less costly option.
  • Triple glazing is more effective at keeping heat out in summer than double glazing.
  • Triple glazing reduces the risk of condensation build-up between panes. The lower `u’ value helps to minimise internal condensation issues as heat is kept inside the building which stops the external temperature reacting with internal warm air, resulting in condensation.
  • Whereas double glazing can create cold patches due to the higher `u’ rating of windows compared to walls, triple glazing reduces this difference in `u’ value between windows and the rest of the building.

The downsides of triple glazing:

  • Triple glazed windows cost more than double glazing (almost double) while the improved `u’ value is not substantial.
  • It takes a long time to achieve pay-back in terms of energy efficiency; triple glazing is not cost-effective and does not result in much better energy savings than double glazing.
  • Thicker glass reduces natural light penetration, therefore less external light enters; also less heat is absorbed from the sun’s energy which can affect the amount of warmth coming into a room.
  • Triple glazing costs more to produce than double glazing and the frames are heavier.
  • Installing triple glazed windows costs significantly more than double glazed windows.
  • There is a longer return on investment due to the high cost of purchase and installation.
  • The extra weight of triple glazed windows could damage weak walls; units need to be installed correctly.
  • Condensation may appear on outer layers of glass; the more heat trapped inside the home increases the likelihood of outside panes remaining cooler, therefore condensation will form in cold temperatures.
The three panes of glass clearly displayed in a triple glazed unit.

Energy performance

The `u’ value is a measure of how easily heat passes through a material. Single glazed windows have a `u’ value of 5; older double glazed units have a value of around 3; modern double glazing comes out at around 1.6 due to improvements such as optimisation of the window cavity, use of low emissivity coatings, inert gas filling the gap between panes and the use of aluminium spacers in frames. 

Triple glazing has a `u’ value of around 0.8, however, on a pure efficiency basis, neither double nor triple glazing will pay for itself. The Energy Saving Trust advises looking for the British Fenestration Rating Council rating when seeking the most energy efficient windows; the rating scheme ranges from A++ to E. The entire window, including frame and glass, is assessed to examine heat loss, draughts and solar gain. The `u’ value will also be displayed on the energy label. In terms of compliance, Building Regulations state that any windows installed must have a `u’ value of no less than 1.6.

Conclusions

Triple glazing may be considered `better’ in the same way that under-floor heating is viewed as superior to conventional heating, and it is the most energy efficient choice; however, it may not be the most cost-efficient solution in terms of the payback period in proportion to savings on energy bills.

A more cost-effective route may be replacing old windows with double glazed units and improved insulation. If the existing double glazing in a property is working, especially if the windows are wood-framed and in good condition, it may be sensible to retain this rather than replacing it with triple glazing. Fitting very thick curtains is also an effective insulating method.

The main reasons for installing triple glazing would be to reduce noise or to eliminate cold spots in a house; it may also be worthy of consideration by anyone building a new property, otherwise double glazing will probably be the better option. If triple glazing is chosen, it is important to ensure that high quality frames are selected and remember that the overall insulation of a house is key to the effectiveness of both double and triple glazing.

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