Double- or triple-glazed units trap air between the panels, which insulates against heat loss and helps to reduce noise transmission. Installing low E-glass as the inner pane in a unit reduces the U values still further. In very high-spec windows, the cavities are filled with argon or krypton gas, which conduct less heat than air.
Window construction and frames also have a bearing on the thermal performance. One of the most popular materials used to make double-glazing units is uPVC. It's cheap, has good insulating properties, can be fashioned into a range of profiles and designs and requires little maintenance. However, as one of the most problematic plastics, it cannot be recommended on ecological grounds. The best insulating material for window frames is wood, either softwood, which is not very durable and needs frequent refinishing, or naturally weather-resistant hardwood, whose sustainable sourcing may cause a problem. Metal frames - such as aluminium - are very long lasting but have high embodied energy and compromise the window's insulating properties dramatically. Composite frames - such as those made of wood powder-coated with aluminium - can offer the best of both worlds
Replacing original windows with double-glazing does not win universal approval in architectural circles because of its visual effect on the elevational detailling of period houses. In conservation areas, or if your home is listed, you may be prohibited from making this type of alteration.
- A range of highly insulating units, double- or triple-glazed.
- May include low-E glass
- Cavities may be filled with argon or krypton gas
- Available off-the-shelf in standard sizes and shapes, bespoke designs are possible
- Very high specification windows include integral blinds operated by controls on the outside
- Price depends on specificatin and framing material
- Substitute glazing to prevent heat loss and reduce draughts