What About Triple Glazing?

Triple Glazed Windows

High performance windows are energy efficient and help contain and conserve heat within the home. They keep out wind and rain and resist condensation but still allow natural heat from the sun to enter the dwelling and provide warmth.

How Does Triple Glazing Compare?

Apart from the number of glass panes, the design of triple glazed windows is fundamentally the same as the design of double glazed windows. In both cases, the air gaps between the glass panes provide the insulating layers that slow down the heat loss and reduce the opportunity for condensation to form.

Recent Developments in Triple Glazing

Until fairly recently, triple glazed windows were produced as an expanded version of double glazed windows and as a result the frames were too deep to be accommodated within standard wall thicknesses and were expensive to produce. Recent developments in triple glazing windows have resulted in slimmer profile frames and flush sash design that are visually pleasing and deliver enhanced performance at an affordable price.

Multiple Glass Panes

It is physically possible to manufacture high performance windows with more than three layers of glazing but, as successive panes are added, thermal value reduces to the point where the thermal advantage does not constitute value for money. Furthermore, with each additional pane of glass, the light transmission and clarity of vision reduce.

High Performance Windows

Whether windows are triple or double glazed, apart from the number of glass panes, they still have the same design features. All new windows are rated using the same criteria, which takes into account their overall performance. House window frames are generally manufactured from low conductivity materials, like softwood, hardwood, pvc-u (u-pvc), glass fibre and composites. Insulated hollow frames can further reduce heat loss and improve comfort.

Low Emissivity Glass (Low-E Glass)

In order to achieve the U-values demanded by current legislation, low E glass must be used in triple and double glazed windows. The low emissive coating allows heat from the sun to enter the building but significantly reduces heat loss from inside by reflecting radiant heat back into the room.

Glass Pane Spacers

The two or three panes of glass are each kept apart by a 'spacer'. Most spacers are constructed of either thin gauge steel or aluminium, for reasons of thermal expansion, stability and cost. To reduce heat transfer through the spacer and to increase overall thermal performance, the spacer may be constructed of fibreglass or a hybrid design of metal and plastic.

Inert Gas Fill

The air gaps between the panes provide the insulating layers that slow down the heat loss and reduce the opportunity for condensation to form. Air is a relatively good insulator but inert gases are much better due to their lower thermal conductivity. The most commonly used inert gas in triple glazing units is argon. The inert gases krypton and xenon are thermally more efficient but are more expensive.

Window Energy Ratings

Certified windows carry a label with the A to E grades. Window ratings are designed to allow accurate comparison of the thermal performance of windows under identical conditions. The ratings take into account the amount of heat lost through windows as well as the volume of air leakage in or out through the window unit when it is closed. Triple and double glazed windows are assessed by the same criteria. Because of the presence of the second air gap, triple glazed windows can be expected to be in the 'A' section of the ratings.

Choosing a Window Type

When choosing windows, it is important to compare the thermal resistance of the external wall with that of the window you intend to fit. If the wall has been constructed to a high thermal standard then it follows that a high performance window should be installed. This could be a highly rated double or triple glazed window. If the external wall is of a low thermal resistance, fitting a high performance window may be of little benefit and unnecessarily costly. In this latter case, double glazing with a lower rating may suffice. Before making the final decision on the choice of window it is advisable to seek advice from an appropriately qualified building professional or a window specialist.

If you would like to know more about double or triple glazing and low E glass why not visit http://www.LowEnergyHouse.com

David Stoppard is the Editor of http://www.ecofriendlybuilding.com/ and a group of associated websites that deal with the issues surrounding energy saving in buildings and renewable energy. The EcoFriendlyBuilding.com websites have evolved from an architectural practice with a keen interest in energy conscious design. Its members have set out to promote energy saving measures, sustainability and renewable energy technology in building, in order to help, protect the environment, secure future energy supplies and reduce fuel poverty.

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