All window companies and sealed unit manufacturers want to avoid the risk of premature IG failure and the subsequent remedial costs incurred, Thermoseal Group’s sales director, Mark Hickox, has advised – he adds that the correct specification warm edge spacer can go a long way to preventing this.

“If the temperature inside a sealed unit increases from 20C to 80C, a spacer bar with a high linear expansion rate could cause the unit to fail prematurely,” Mark said. “And the problem is only going to get worse as units get larger and the climate warms.

“The spacer bar in a unit that measures 2m on any length could expand by up to 16.92mm during daylight hours. Since the ends are fixed, the bar could bow like a rainbow within the unit, while forcing the panes of glass apart, weakening the PIB sealant in the process.

“This would allow moisture in and cause the unit to fail.”

Mark explained that as rigid plastic tube has replaced aluminium spacer bar in recent years, the problem has got worse, because not enough attention has been made to the plastic compound.

“Our Thermobar rigid spacer bar is an engineering plastic made up of 40% glass fibre,” Mark said. “This means its coefficient of linear expansion is actually an improvement on aluminium spacer bars which in terms of physical characteristics have been the benchmark for more than 50 years.

“But not all rigid spacer bars can say the same. Some warm edge bars have been found to contain no glass fibre while one major manufacture is promoting a product with 20% glass fibre, which means they will expand far more than aluminium, putting the unit at risk once installed – especially on south-facing windows.”

Mark said linear expansion is one of many issues facing sealed units as cheaper IGU components enter the UK market. Another one is UV-stability.

“Once that unit is installed on site, it is affected by the sun, the heat and by the wind and rain,” Mark said. “That is why we have invested in our testing facilities and laboratory, to ensure that the components we supply will exceed the expected lifetime of the unit.

“This includes UV stability. Not only do we want the colour to last for many years – and colour is increasingly important for homeowners – we also don’t want to see the product’s physical properties degrade, which could cause the unit to fail.”

Thermoseal Group has invested in a Q-Sun test chamber, which can accelerate the effects of the sun’s rays. The component supplier puts all its products – including spacer bars, corner keys and Georgian bar – through these intensive cycles to ensure that they won’t cause a unit to fail for purely cosmetic reasons.

“And because we supply all IGU components, we can test them working together, to confirm that there is long-term capability,” Mark said. “And as part of the Fenzi Group, we now supply the most comprehensive range of IGU components, all guaranteed to perform for the lifetime of the unit, and beyond.”