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Double glazing





Note: There will be a very long payback period

All properties lose up to 30% of heat through windows. Energy-efficient glazing can keep your home warmer and quieter as well as reducing your energy bills. That might mean double or triple-glazing.

Double-glazed windows have two sheets of glass with a gap in between, usually about 16mm, to create an insulating barrier that keeps heat in. This is sometimes filled with gas. Triple-glazed windows have three sheets of glass, but aren’t always better than double-glazed windows. To choose the most energy-efficient window look for the BFRC ( British Fenestration Rating Council).

Money saving tips

Savings when double glazing is installed

The costs and savings for energy-efficient glazing will be different for each home and each window, depending on its size, material and the installer you choose. Double glazing should last for 20 years or more and over that time the savings shown could more than pay for the cost of the initial installation.

It can reduce your energy spending by £235 (=432kg CO₂ per year), according to the Energy Saving Trust.

Double glazing may also add up to 10% to your home’s value, and makes it much easier to sell when that time comes. It also makes your house warmer, cuts your carbon footprint, and reduces noise from the outside world so is a good long term investment.

It is estimated that  94% of English homes and 93% of Scottish homes have double glazing. At these levels the government do not believe a grant scheme is worth implementing, so the cost for new windows has to come out of your own pocket.

Energy efficient windows

Energy-efficient windows come in a range of frame materials and styles. Performance criteria vary according to the following:

  • How well they stop heat from passing through the window.
  • How much sunlight travels through the glass.
  • How little air can leak in or out around the window.

Benefits of energy-efficient windows

  • Smaller energy bills.
  • Smaller carbon footprint.
  • More comfortable home: energy-efficient glazing reduces heat loss through windows and means fewer draughts and cold spots.
  • Peace and quiet: as well as keeping the heat in, energy efficient-windows insulate your home against external noise.
  • Reduced condensation: energy-efficient glazing reduces condensation build-up on the inside of windows, however replacement windows will be more airtight than your original frames, so condensation may build up due to the reduced ventilation. If your house does not have much background ventilation, look for replacement windows with trickle vents incorporated into the frame to let in a controlled amount of air.
  • More secure than single paned windows.

Environmental tips

Environmental Parameters

  • Glass: The most energy-efficient type for double glazing is low emissivity (Low-E) glass. This often has an invisible coating of metal oxide, normally on one of the internal panes. This lets in light and short wave length infra-red energy, however reflects back the long wave length infra-red radiation generated by the interior furnishings.
  • Gaps between the glass: Very efficient windows might use gases such as argon, xenon or krypton in the gap between the sheets of glass.
  • Pane spacers: These are set around the inside edges to keep the two panes of glass apart. For maximum efficiency, look for pane spacers containing little or no metal – often known as ‘warm edge’ spacers.
  • Hermetically sealed double glazed units.
  • uPVC frames last a long time and can be recycled.
  • Wooden frames may have a lower environmental impact, but require maintenance. They are often used in conservation areas where the original windows had timber frames.
  • Aluminium or steel frames are slim and long-lasting, and may be recycled.
  • Composite frames have an inner timber frame covered with aluminium or plastic. This reduces the need for maintenance and keeps the frame weatherproof.
  • U-Value (sometimes called a heat transfer coefficient) is used to measure how effective the elements of the window are at preventing heat from transferring between the inside and the outside of a building ie how much heat loss it allows. Materials that let out more heat have higher u-values. In some cases, windows with a higher energy performance rating might have a higher u-value than windows with a better energy efficiency rating. This might seem the wrong way round as lower u-values indicate better insulation levels. However, in these cases it will be that there are other aspects of the window that make them better overall such as coating used on the glass and the gap between the glass panes.