Reduced sightline IGU issue addressed

Following recent news coverage in Glass Times regarding the manufacture and compliance of some reduced sightline insulating glass units, the GGF has addressed the issue from a technical and GGF policy perspective.

The GGF has also threatened to expel members if they break GGF rules and the law. However, it said it wasn’t a policing authority and it recognised that companies could be put under pressure from planning officers to make non-compliant products.

With regard to whether or not narrow cavity IGUs comply with building regulations, Steve Rice, GGF director of technical affairs, said: “In all countries within the UK there are provisions for non-compliance with the general thermal requirements in properties that are classed as heritage assets (listed buildings), and conservation areas where the use of compliant products would significantly change the fenestration of the building.”

For example, in Scotland, clause 6.0.3 general guidance states: “Work on existing buildings – as for other standards within Scottish building regulations, the energy standards apply to conversions and also work on existing buildings, such as extensions, conservatories, alterations and replacement work. However, in some situations, individual standards may not apply or guidance on compliance with the standards may differ for such work. The latter is usually to recognise constraints that arise when working with existing buildings.”

Steve said that building regulations in the other countries within the UK also have a similar allowance.

“The issue in question is not compliance with building regulations but compliance with the requirements of the Construction Products Regulations and through that, compliance with BS EN 1279-5:2005+A2:2010 – Glass in building – Insulating glass units – Part 5 Evaluation of conformity,” Steve said.

BS EN 1279-5 requires all IGUs to have Type test (TT) evidence to Parts 2 and 3, component manufacture evidence to Part 4, and a system description in accordance with the requirements of Part 1. A Factory Production Control (FPC) is also required at a minimum level detailed in Part 6.

The Part 2, 3 and 4 test evidence is required to demonstrate durability of the IGU, to provide a reasonable service life.

Russell Day, GGF director of Home Improvement, said: “In terms of the demand for the IGUs in question, it is not the narrowness of the cavity but the reduced sightlines of the spacer bar, some being as low as 5mm from edge of glass to top of spacer bar. This market demand is generated, in the main, by local authority planning officers – in particular, conservation officers – who demand that replacement glazing or windows into listed properties must be glazed into glazing rebates, either in the frame or sash that limits the dimension between edge of glass and top of spacer bar.

“This is of particular relevance where the sash is sub-divided into small panes such as is seen in Georgian style properties. Planners commonly restrict the width of glazing bars which sub-divide sashes into small panes; it is common to see these restricted to between 18mm and 22mm, which in turn results in glazing rebate upstands in the range of 6 to 8mm, leaving a feather of 6mm to support and provide a level of strength to the window sash.

“To ensure IGUs comply with these planning requirements the GGF aims to work with stakeholders across the supply chain. A number of years ago, an IGU manufacturer produced reduced sightline IGUs by cutting down existing 5mm high warm edge spacer bars to produce a spacer bar with a 3mm height and combine this with as little as 2mm or less sealant. It was reported that there was a high failure rate of these units which saw the introduction of a warm edge spacer bar manufactured with a 3mm high spacer.

“This has been marketed based on an edge-seal construction incorporating a minimum 5mm of sealant over the back of the spacer bar, giving a minimum sightline of 8mm. Although the spacer bar manufacturer has not been able to achieve passes to both Part 2 and 3 of EN 1279, they are continuing to work on developing a system that will achieve passes to both parts of the standard.

“The issue that IGU manufacturers now have is that given planners are imposing these conditions on heritage buildings and in conservation areas, these non-compliant IGUs will be undoubtedly be manufactured by some companies.”

Phil Pluck, GGF Group chief executive recently addressed the issue at the GGF’s annual Members’ Day, saying “reduced sightline units is an area that is simply not a case of black or white”.

“If a member chooses for their own advantage to breach the GGF rules or indeed the law, it is the GGF’s duty to inform them and to guide and support them to return within the boundaries of the GGF rules and the law,” Phil said.

“If they choose to ignore that guidance then upon a finding of guilt they will be expelled. We have evidence that that course of action has worked in the past. But we are not a policing authority.

“However, if we find that a member is operating outside of the GGF rules because of other authorities’ failings then it is the GGF’s duty to both guide that member and address the root cause that is putting that member under pressure to act in a way that takes them outside of the GGF rules.”

Phil argued that architects, planning authorities, heritage groups, and the Chartered Trading Standards Institute all have a part to play to address this issue.

“Simply isolating and punishing one part of that supply chain – ie, our members – will not address the underlying issue that affects the entire industry,” he said.

The GGF has worked mainly in Scotland on this issue, having meetings with Historic Environment Scotland, Building Control, MSPs and Scottish ministers, Trading Standards, and local authority planning departments. Generally, the view from most is that although they accept the reduced sightline IGUs being supplied do not comply, and although early failure of these IGUs has been experienced, the view of most agencies is that heritage takes precedence to compliance with BS EN 1279.

The GGF also said it has referred one manufacturer to Trading Standards, which has yet to report on the case.

Steve Rice said that stopping the supply of components used to manufacture these products, “will result in a reversion to the practice of cutting down an existing product that is likely to result in a return to significant numbers of IGUs failing very prematurely”.

He continued: “The GGF has undertaken a number of site inspections of this type of IGU installed in timber windows where the homeowner has complained of IGU failure (condensation in the cavity). We are informed a number of these are pursuing a legal resolution to their issue.”

Insulating Glass Units (IGUs) – Conforming to the Construction Products Regulation (CPR) –  is available as a free download: