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Quality affects longevity when it comes to double glazing

Double glazing units are a simple idea – two panes of glass with an air gap between is a much better insulator than a single pane. This simple idea can reduce the thermal conductivity by up to 83% and can now be so efficient they actually heat the room. But to keep them working effectively and the benefits flowing they need to be looked after. The most critical part of a unit is the perimeter seal. So how long do double glazing units last?

Units will perform differently depending on various factors including: Cross section diagram of double glazing unit

  • the quality of materials and construction:
  • the stress they suffer. Periods when the temperature gradient between the two panes is extreme will reduce the life, so a window facing south or in a very cold climate or with a smaller gap will fail sooner. Units typically last from 10 to 25 years, with windows facing south often lasting less than 12 years. Typically this arises because the adhesive holding the spacer bars and panes together fails when the spacer bars try to twist due to temperature gradients. Once the adhesive has failed in one spot, water can enter the unit and condensation will occur.
  • perimeter seal. The perimeter seal is designed to protect the air gap between the panes and comprises a typically butyl mastic retaining a desiccant within a perforated metallic spacer bar. The desiccant absorbs any moisture in the air gap. The most frequent cause of failure is excess moisture around the seal which over times causes the butyl to fail and to allow moisture into the air gap. This overwhelms the desiccant so that the unabsorbed moisture condenses on the colder surface.

So whilst you cannot change where you live or your climactic conditions it is important to find a supplier that uses the best materials and ensures the perimeter seal is well protected from water. All of our standard casement and sliding sash windows are manufactured with an internally beaded system, which is mastic capped externally. This prevents water from reaching the glazing rebate. We also integrate a drainage channel in the base of the glazing rebate, as a secondary defence against water pooling. And of course we use the best materials available, which come to us with performance warranties. See some of the key differences in our products here.

We are so confident in our glazing techniques that our sealed units on standard products come with a full 10 year guarantee against failure, which includes both the material cost of the unit and the labour cost of the replacement. This is significantly better than other guarantees in the marketplace.

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