Kevin Underwood, British Woodworking Federation. Credit: Professional ImagesNew guidance has been published by the British Woodworking Federation (BWF) to help firms placing orders for insulating glazing units (IGUs) including narrow cavity or ‘slim’ glass units.

Such units – highly energy efficient, hermetically sealed units designed to keep homes warmer in the winter and cooler in the summer – usually consist of two or more panes of glass separated by a spacer material and sealed together at the edge. The space between the panes is filled with air or an inert gas such as argon or krypton which, together with a low-emissivity glass coating, produces the unit’s excellent insulating properties.

‘Slim’ units have cavities of 8mm or less and often have a reduced edge seal and they are favoured in listed buildings or conservation areas as they allow thinner timber profiles and bead detail.  They have become very popular after being featured on the ‘Grand Designs’ TV programme.

However, concerns have been raised by BWF members about the quality of some of these units supplied by a range of different manufacturers. Further investigation by the BWF has also highlighted that there are some ‘slim’ IGU suppliers who are seemingly unable to provide the appropriate test evidence required to ensure performance of the unit in the long term.

Kevin Underwood, BWF Technical Director, says:

“We have received a number of queries through the BWF technical helpline and in our technical committee and council meetings particularly concerning certain ‘slim’ insulating glass units on the market. The new guidance addresses this concern, helping buyers to exercise appropriate care and ensure that when purchasing IGUs they know what to ask for and what they should expect from supporting documentation from their suppliers. IGUs that have been suitably tested and manufactured in a controlled manner should provide the levels of performance our members are looking for.”

Kevin Underwood points out that CE marking for glass units became mandatory on 1 July 2013, so this should help buyers of all types IGU that are covered by the harmonised standard BS EN 1279-5.

The BWF is advising its members to seek confirmation from suppliers that all the IGUs, both ‘standard’ and ‘slim’ types will be CE marked and will meet the requirements for the durability of glass units given in the BS EN 1279 series of standards.

Kevin Underwood explains that buyers should insist that units should only be supplied when there is the correct and full test evidence to accompany them:

“In order to establish that the test evidence applies to the glass units which you’re intending to buy, you should ask the supplier for a copy of the system description, and check that this is fully consistent with what you’re buying,” explains Kevin Underwood.

“The IGUs should also have been tested for durability, which means meeting the requirements for moisture penetration, gas leakage if appropriate, and edge seal strength. The production of the IGUs should also follow a Factory Production Control system and periodic testing meeting the requirements of BS EN 1279.”

Members are also advised to discuss the length of warranty that is being offered by their glazing suppliers on these units and to check the detail as to what these warranties will cover. They should also confirm that they will employ an acceptable glazing method using appropriate and compatible materials in an effort to avoid future problems.

A copy of the BWF fact sheet on Slim IGUs can be downloaded at:

http://www.bwf.org.uk/assets/bwf-igu-advice.pdf