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Do Triple Glazed Windows Make Sense?

Selecting the proper glazing is a huge investment for a home, so if you’re thinking about getting triple glazed windows or secondary glazing, here’s our guide to help you decide whether they are worth it.

These days, triple glazed windows have increasingly become popular amongst window suppliers – especially in the aluminium space – but long-standing worries concerning the real advantages prevailing over the perceived costs are still on the minds of homeowners.

It’s a difficult decision that self-builders face when it comes to specifying their final finishes and given how the price of triple glazed windows is about 20% more compared to double, why should anybody opt for it? Backers believe that it’s more about comfort and quality and that self-builders should factor in triple glazing for the same reason they fit underfloor heating: it’s better.

Here’s what you need to take into account when evaluating the benefits and drawbacks of whether triple glazed windows are worth it.

What is a Triple Glazed Window?

In a nutshell, as obvious as it may seem, triple glazing comprises three glass panes within a sealed frame, just like how double glazing has two panes. Between every pane is a pocket of an inert gas like argon; as compared to air, argon is heavier and works as an insulator for both heat and noise.

The third glass pane situated halfway between the outer and inner panes of double glazed windows creates two airlocks that enhance the energy efficiency of double glazing by about 50%.

Energy efficiency is enhanced further by variables like the type of gas or air used in the space found between the panes, coating on the glass to minimise energy loss, and warm edge spacer bars to minimise thermal bridging. The frames also play a significant role in the overall functioning (and the insulation too). Look for insulated frames that have a decent airtightness rating.

Is Triple Glazing Better than Double Glazing?

Energy Performance

The tried and proven method used to compare the energy efficiency of windows is the U value measurement system, just like with roofs, floors, and walls.

Glassmakers have become masters when it comes tinting and coating glass with all sort of finishes which keep unwanted sunlight away, heat in, minimise glare and even self-clean as well. The end product of this glass engineering means that the U values of the glazing have been diminished significantly.

Single glazed windows have a U value in the range of 5.0W/m²k

In the past, Double glazed windows had a score of more than 3 and can now attain a value of 1.4 (Velfac have 1.36). Because of these advancements in the manufacturing process, Building Regulations mandate that windows installed today should have a U value of at least 1.6

The Passivhaus standard stipulates that triple glazed windows have a U value not exceeding 0.8, but there are suppliers claiming to have achieved just 0.5

The U value required for walls is now below 0.3 showing just how windows remain weak areas in the general thermal efficiency of a building envelope. Thus the considerable pressure to enhance their performance even further.

Manufacturing Improvements in Glazing

Advances have been brought forth by the introduction of:

Low-emissivity coatings getting applied to the glass to prevent heat from escaping

Wider cavities in the middle of the two glass panes. The optimum distance is 16mm

The cavity getting filled with inert gas, often argon

Crafting cold bridges like aluminium spacers, enclosing the glazed units