Double or triple glazing? The choice is yours!

When making your mind up whether to go for double or triple glazing, ask yourself which is going to be the better long term product for your property?, as genuinely “A+” rated energy saving double glazed replacement window products are more than sufficient for the vast majority of UK properties.

Not all replacement windows are “A+” rated by any means, as to achieve a genuine energy rating that is high enough to comply with the current Building Regulations requirements for greater thermal efficiency, the frame of the window (whether it is made of aluminium, crittall, hardwood or UPVC) needs to be independently tested in conjunction with the sealed unit and gaskets.

The current Building Regulations in England and Wales require both home owners and double glazing manufacturers and installers to supply and fit replacement windows with a minimum energy rating of “C” or a maximum combined U-Value of 1.6 W/m2K (a measure of thermal efficiency, where the lower the figure the greater the energy efficiency of a product).

As “A+” rated double glazed replacement windows and “A++” rated triple glazed replacement are both “A+” rated or better, there is frankly not much thermal difference between the levels of thermal performance. It is really a question of which product will give you the best return on your investment, plus whether double or triple glazing is best suited to your particular property and requirements.

Nowadays, although they do cost more, triple glazed UPVC windows, residential doors and French doors are not a great deal more expensive than double glazed products. Properly installed “A+” rated UPVC double or triple glazing offers unrivalled value for money when household energy savings and consequent financial savings are taken into account (i.e. painting and decorating).

However, as triple glazing has an extra pane of glass, each sealed unit is thicker and heavier duty. So not only does the extra glass cost at least 50% more, each window and/or door costs more to transport as is much heavier. One word of caution, historically triple glazed sealed units tend to break down/fail thermally more often than double glazed units, so this factor needs to be taken into account, along with the extra costs of triple glazing when choosing between the two different types.

Top quality UPVC triple glazing, with a U-value of 1.0 W/m²k, can potentially be around 40% more thermally efficient that standard “A” rated double glazing and 60% more thermally efficient than standard “C” rated double glazing.

Even though most UK property owners will find replacement “A+” rated double glazing perfectly adequate for this modern energy saving age, some may still think that triple glazing is worth the added investment for five reasons:

1)    Triple glazing can deliver approximately 40% more thermal efficiency than standard “A” rated UPVC double glazing so energy savings should be far higher.

2)    Triple glazed windows and doors will further reduce draughts and cold spots in a room that currently has less thermally efficient windows and doors.

3)    Triple glazed windows and doors can also further reduce the impact of exterior noise. They do reduce noise, and if the middle pane of glass is a different type of glass to two external panes, this also helps toward acoustic insulation.

4)    Triple glazed windows and doors could save each UK home owner over £10,000 during the next 20 years, which is not inconsiderable when the rising costs of fuel are taken into consideration.

5)    A 3rd pane of glass, by definition, makes a triple glazed sealed unit much harder to break than a double glazed sealed unit – especially when the middle pane is made of toughened glass. What’s more, many UPVC double and triple glazed windows are internally beaded and the glass unit can only be removed from the frame by a person who is inside the premises.

It is important that triple glazed windows have a toughened middle pane even if the two outside panes are float glass, as this helps prevent thermal breakage of the middle pane. Thermal breakage of the middle pane can occur when there is a considerable difference in the indoor and outdoor temperature of a property. Because the thermally efficient triple glazed sealed unit keeps more heat in, the internal pane will remain at roughly room temperature. Similarly, because less heat is escaping, the external pane will remain cold when it is cold outdoors. Therefore the middle pane of glass is subject to very contrasting temperatures i.e. warmth from the internal pane/cavity and cold from the external pane/cavity, and thermal breakage could occur if standard annealed glass was used. By using toughened glass, the possibility of thermal breakage is all but eliminated.