Low Sightline Insulated Glass Units

Low Sightline Insulated Glass Units

The Glass and Glazing Federation recognises the rise in the number of Insulating Glass Unit Manufacturers producing narrow cavity IGUs with an edge-seal sightline of 5-6mm to meet the need for improved energy performance of windows within the Heritage Sector.

This has increased demand within the UK for windows and doors glazed with Insulating Glass Units with either cavity widths between 4mm and 8mm or edge seal sightlines (edge of glass to top to spacer-bar) below that normally used in the construction of IGUs or a combination of both. This demand is being created by local planning and conservation guidance that requires IGUs to be glazed into timber windows with through-glazing bars with lower than normal rebate depth.

The requirement for IGUs to be placed on the European market is regulated by the Construction Products Regulations (CPR). The IGU should be manufactured in conformity with the harmonised European Standard (hEN) EN 1279-5 and conform to all other parts of the series, EN 1279 parts 1 to 4 and EN 1279-6. In order to comply with this standard, Type Testing to EN 1279-2, ‘Long term test method and requirements for moisture penetration’ and EN 1279-3, ‘Long term test method and requirements for gas leakage rate and for gas concentration tolerances’, must be undertaken by the IGU manufacturer. IGUs with reduced sightlines below 8mm need to have achieved passes to both parts 2 & 3 when tested to these standards. There is also a requirement under EN 1279-4, ‘Methods of test for physical attributes of edge seals’, for the manufacturer of the edge-seal components to confirm that the manufactured edge-seal dimensions provide sufficient strength to enable the IGU to withstand the stresses exerted on it by wind-loading.

For an IGU to be durable and to provide a viable, economical service life, positive Type Test results for parts 2 and 3 are required and the edge-seal component manufacturers must provide confirmation that the construction is suitable by providing information in accordance with EN 1279-4.

The GGF’s position on the manufacture of IGUs is that all IGUs placed on the market in the UK must have achieved passes to EN 1279 parts 2 and 3, and have an EN 1279-4 component manufacturer confirmation. Any manufacturer producing these reduced sightline IGUs must meet the requirements of the CPR in Great Britain and Northern Ireland.

It should be noted that a majority of these reduced sightline IGUs are also manufactured with cavity widths of 4mm, 6mm or 8mm and although these cavity widths should not affect the results of EN 1279 part 2 testing, some concern has also been expressed regarding the ability of these narrow cavity IGUs to be gas filled within the concentration limits required and therefore their ability to achieve an EN 1279-3 pass.

Since the end of 2014, in an attempt to resolve the issues with planning specifications and the inability of low-sightline IGUs to achieve positive results when Type Tested to EN 1279 parts 2 and 3, the GGF have been in discussion with various groups and have given a number of presentations to Local Authorities in Scotland. These presentations have highlighted the issue of durability and early failure of this type of IGU and although positively received, these IGUs continue to appear as a condition in planning consents. The GGF’s primary focus has been to work with Historic Environment Scotland and help them review their Guidance, ‘Managing Change in the Historic Environment – Windows’ and guide planning officers, when replacing windows or in new build situation, towards using modern manufacturing specifications, thereby removing the demand for these non-compliant EN 1279 IGUs. The GGF have commented on the latest version of the guide and are now awaiting the amended revision to review before publication.

The GGF have also been involved with a number of other groups in an attempt to highlight the issues when installing this type of IGU. These groups include the Scottish Planning Enforcement Officers Forum, Local Authority Building Standards Scotland (LABSS), Head of Planning Scotland (HOPS) and the Energy Savings Trust. A number of meetings and discussions with MSPs have also taken place and we have acted on their advice in attempting to move this issue forward.

The GGF remain open to working with these groups in an attempt to educate Planning Officers, Building Control Officers and Trading Standards Officers to help provide end users (homeowners, Local Authorities and Housing Associations) to protect them from the potential significant future costs of early replacement of these non-compliant IGUs.