BSI Laboratory Showcase

Hemel Hempstead Centre of Excellence

Each quarter we plan to showcase our testing capability and expertise, and this quarter our focus is on the service we provide for double glazed insulating glass units undertaken at our Centre of Excellence in Hemel Hempstead. 

BSI’s subject matter expert, Paul Whitehorn, Certification Manager, Fenestration, shares his knowledge on how we test double-glazing units underpinned by the requirements of the BS EN 1279 suite of standards.

Our certification & testing teams have over 40 years of experience in certifying and testing insulating glass units. Whether clients require direct commission testing, or to achieve a BSI Kitemark, we offer an unbiased and independent service on which they can depend.


BS EN 1279 suite of standards

BS EN 1279 suite of standards cover double glazed insulating glass units that greatly improve the thermal performance of windows and doors.

BS EN 1279-1 contains the generalities, dimensional tolerances and rules for the system description.

BS EN 1279-2 covers air filled units. All BSI Kitemark approved units must comply with this standard.

The standard measures the ability of the unit to keep moisture out of the cavity between the two panes of glass that can cause unsightly condensation inside the unit.

If a manufacturer wishes to further improve the thermal performance of the unit they may fill it with an inert gas such as Argon or Krypton, when this happens they must then comply with both BS EN 1279-2 & BS EN 1279-3.

BS EN 1279-3 measures the units ability to retain the inert gas, so you can be confident that it will retain the gas for a minimum duration. Our test engineers measure the initial content of the gas and also the leakage rate, once the leakage rate has been established then we evaluate the compliance of the unit.

All clients holding a BSI Kitemark also have their required periodic testing completed in accordance with BS EN 1279-6, these recheck the requirements of Parts 2 & 3 in a reduced form and are completed on a 6 monthly basis, and this frequency can be reduced once enough positive evidence is produced.

In addition to moisture penetration and gas concentration tests Part 6 also has a “Fogging” test, this ensures that any decorative components do not release any harmful chemicals once directly in UV light, these can form inside the unit that appears to be condensation but it is in fact non-water based vapour.


The duration of our tests

  • BS EN 1279-2 takes approximately 4.5 months to complete as they are placed into test chambers as various temperature/humidity cycles as strictly defined by the standard.
  • BS EN 1279-3 takes 3.5 months to complete as the leakage rate of the unit has to be established for complete accuracy.
  • BS EN 1279-6 usually takes 6 weeks to complete but an individual UV fogging test is around 2 weeks if no fogging occurs.


The accuracy of our test equipment

All test equipment is calibrated and our fenestration laboratory runs in accordance with ISO/IEC 17025:2005. ISO/IEC 17025 specifies the general requirements for the competence to carry out tests and/or calibrations, including sampling. It covers testing and calibration performed using standard methods, non-standard methods, and laboratory-developed methods.

The test facility is fully accredited to ISO/IEC 17025 for parts 2, 3 & 6 and certification to ISO/IEC 17065 by the United Kingdom Accreditation Service. We are also a Notified Body & Approved test laboratory, meaning our results can be universally accepted around the world with confidence.  


The BSI Kitemark™ Advantage

Exclusive to BSI, the BSI Kitemark is a quality mark that shows a construction product or service meets the applicable and appropriate British, European, international or other recognised standard for quality, safety, performance and trust.

This has helped our clients to differentiate themselves from their competition, to prove their product is reliable and safe, and gives them enhanced efficiency and trust in their products out in the marketplace. Discover how BSI Kitemark has helped clients boost their business.


For more information on our full range of testing and certification services for windows, doors, double-glazing and more, visit

If you would like to visit our laboratory to view our testing facility for sealed units, or for more information, please contact our team on +44 345 0765 606, or email