Double glazing will need replaced after a while due to the nature of the design – the gas that separates the two window panes slowly leaks out over time meaning the energy efficiency of your window is compromised. If your double glazing allows cold spots; water to seep through the frame; has cracks or chips in the window or has a build-up of condensation between the two panes of glass (misted windows), you should probably look into getting your double glazing replaced or repaired.