Excerpt taken from a story by Joe Lynam - BBC World Service business reporter

One of the biggest revolutions in the look of Britain's buildings in recent years has been in windows.

The British government's efforts to cut energy use in homes has singled out windows for special attention.

All new and replacement windows now have to be double glazed to cut heat loss.

Consequently, wooden window frames have given way to uPVC framed double glazing, which is cheaper to buy and install than double glazed timber frames.

In fact, wood double glazing can cost up to three times as much as uPVC double glazing.