Double Glazing

Double glazing helps reduce heat lost through windows as the air between two panes of glass acts as a good insulator. In most replacement double glazing units, the two panes are sealed around the edges, and fitted into a purpose made frame, allowing the air (or an inert gas such as Argon) to be trapped, improving its performance.

Secondary Glazing

Secondary glazing is where a second layer of glass or clear plastic is fitted inside an existing window/door frame but does not have an airtight seal and so is not as effective as installed double glazing. Both types of double glazing reduce the heat that would otherwise be lost from the inside of the building to the outside.

Secondary glazing substantially reduces draughts and is better than most double glazing at reducing noise pollution, although it has less effect on thermal insulation.

It is however appropriate for older buildings that wish to retain their windows but need to improve their thermal insulation. Secondary glazing is extensively used in Listed Buildings and those in conservation areas subject to planning approval and is recommended as a solution by English Heritage.

Triple Glazing

Triple glazing provides an extra layer of protection compared to double glazing.

You will save more on your heating bills than you would with double-glazing. Prices for triple glazing are typically 20 - 40% more than for good quality double glazing.  

Triple glazing units can be sealed with all three panes in a single unit, or can be designed so that two of the panes form a sealed unit (often coated internally with a low-emissivity coating to reduce heat losses further), with the third pane separated by a larger air gap.

This improves sound insulation and the third pane can sometimes be opened to allow a small blind to be fitted inside the unit.