The question of longevity in sealed double glazing windows is not a technology issue, but one of cost.
To allow products to be priced competitively, the seals specified in insulating glass units are good enough to outlast the warranty promise made to the customer, and in the majority of cases, longer. As Mr Collins rightly points out, these warranties are typically between 5 and 20 years, although actual lifespans can be much longer.
Buyers know from the outset how long the units they specify are expected to last, so replacement costs should be relatively easy to anticipate.
It’s important to note that for most projects, using double glazing rather than single will pay back the additional energy required to manufacture it in a short period of time, often just a few months. A unit that is replaced after eleven years or more will have already returned its energy cost many times over.
This is also the case with triple glazing which, although it takes a longer to pay off its energy debt, will still easily manage it over a relatively short period of a few years.
The same is true financially, and the significant reduction in energy costs mean upgrading from single to double or triple glazing will deliver net savings rapidly in most cases, and the pay-back time will only get shorter as the cost of energy increases.
Insulating glass units sold in the UK should be CE Marked in accordance with BS EN 1279, conformity with which includes requirements to pass long-term durability tests.
It is perfectly possible to design units with a much longer lifespan, but this means applying more and better-quality sealant and perhaps even adding additional seals – all of which increases material costs and manufacturing times, resulting in a higher-priced window.
These products do exist. Pilkington Spacia™ is a good example. It makes use of a narrow vacuum cavity to deliver thermal performance that equals that of traditional double glazing despite being only a quarter of the thickness. The heavy-duty seals required to maintain the vacuum also has the effect of increasing the lifespan. The standard warranty for Pilkington Spacia™ is 10 years, but we know from experience that this product lasts much longer.
Of course, the lifespan of insulating glass units will only be maximised if installed correctly and according to the specification for the specific window in question, so installers also play a key role. Poor installation can significantly reduce lifespans.
Glazing technology has come on in leaps and bounds in the last decade, so those with double glazing units reaching the end of their lives have a great opportunity to benefit from new products that will give them much better energy performance and a longer lifespan.
Ultimately, the commercial decision over which products to specify lies with the building developers, and their contractors have a responsibility to ensure they have the information at their fingertips to allow them to make the best choice.
Regards,
Phil Brown, technical advisory service manager (UK & Ireland) and European regulatory marketing manager at Pilkington
