If you start to see condensation building up around your windows, there may be a damp problem in your home. As a general rule damp occurs when there is inadequate ventilation, inadequate heating, inadequate insulation or a combination of these. If you've started to notice condensation in between the panes of glass in your double-glazing units then it is likely that the seal is broken, and the unit will need to be replaced.

Sealed units are manufactured using two panes of glass of the same or different thickness. The most common glass used is 4mm float, which is not a safety glass; this is sometimes backed with an obscure glass. Where safety glass is required, the units will be made from toughened annealed or laminated glass.The two panes of glass are washed so as to have all the dirt and grease removed. They then have an aluminium spacer bar set between them.

This bar generally has the two longest lengths filled with desiccant, which absorbs any moisture within the unit. There are also small holes in the spacer bar, which allow the desiccant to breath. The spacer bar has a primary butyl seal added to both sides of it. The unit is then placed into a press to make sure the primary seal is intact. Once the unit has been pressed it is visually inspected and the secondary seal is then applied. The unit is then cleaned and ready for delivery.

For all frame materials there are windows available in all energy ratings.

UPVC frames last a long time and can be recycled.

Wooden frames can have a lower environmental impact, but require maintenance. They are often used in conservation areas where the original windows were timber framed.

Aluminium or steel frames are slim and long-lasting, and can be recycled.

Composite frames have an inner timber frame covered with aluminium or plastic. This reduces the need for maintenance and keeps the frame weather proof.

You can save yourself considerable amounts of money by replacing the glass sealed unit and not having the whole window or windows replaced. Sealed units are suitable for replacement in windows, doors and conservatories. The thing to remember is that you need to find a company or contractor which is reliable and has built up a good reputation in the field. A good company will ensure that they provide sealed units replaced and guaranteed to last for about 20 years. There are plenty of cowboy operations in this field and this is why you need to be aware and try to get a personal recommendation.