Changing Standards

Jim Lowther Sales Director, and David Law Technical Manager at Xtralite lobby to raise the minimum standard requirements in overhead glazing for public safety.

On occasions, a conflict of industry standards and the harsh reality of safety implications in practice can become apparent and during routine product testing, discrepancies in the British standards supported by the National Association of Rooflight Manufacturers (NARM) were discovered, potentially compromising public safety.

BS 5516-2:2004 currently specifies that, for overhead glazing installed no greater than 13m above the floor, it is perfectly acceptable to specify toughened glass for the inner most pane; something we believe could prove to be dangerous to users of the building. A more sensible specification should always comprise a laminated glass as an inner leaf in a double glazed unit.

The specification and utilisation of rooflights that comprise a dual toughened glass system, it would appear, may put building users at risk and we suggest to industry professionals to call for change in the minimum standards. The Centre for Window and Cladding Technology (CWCT) are a leading light in the classification and testing of glass; the requirement to provide glazing systems in line with their Technical Notes 66 and 67 is becoming much more common place. Indeed, the 2014 edition of the ACR[M]001 ‘Red Book’ acknowledges that “the unique safety issues associated with glass” make the standard ACR test inappropriate for rooflights of glass, and that the CWCT classifications and tests should be adopted.

Toughened glass, once broken, has no ability to support its own weight; let alone the weight of persons who may have fallen onto it. It is often regarded as safe, due to the way it is designed to fail, and fall as small ‘dice’; however, this is not always the case, and physical testing carried out by Xtralite has shown that toughened panes can fall as one large section of glass. The term “safety glass” when applied to toughened glass relates to its ability to avoid severe laceration in low level vertical glazing in the event of a person accidentally falling against the glass, it does not mean that it is “safe” for overhead glazing. To say that this is acceptable up to a certain height is not right, and we urge fellow industry professionals to recognise the impact this could have on building users and maintenance staff and support our call to action.

Laminated glass upon fracture is held together by the interlayer(s) between the panes, holding the broken shards preventing injury to those below the rooflight. Furthermore, dependent upon the thickness of the panes and type / thickness of the interlayer selected, laminated panes will not only support their own weight and remain in situ if broken, but will also have the ability to hold a load lying on the glass, such as an injured person; something which is required to be tested under TN 67. And, with more and more glass being installed in school roofs for example, to specify anything less than the standards we are calling for could pose a real risk to the children passing below. 

Testing recommendations
As mentioned, such safety considerations are supported by The Centre for Window and Cladding Technology (CWCT) a leading information provider in the field of building envelopes and glazing.

It is important to note that the specification of a tested, or similarly approved glazing specification alone cannot be considered to meet the requirements of CWCT. Technical Notes 66, 67 and 92 (which recommends glass specifications which are ‘deemed to satisfy’ the requirements of a Class 2 roof) state that these glass units must be installed into a glazing system which has been tested, and proven to meet the requirements for the given roof classification. The frame and fixings all have an impact on the composition of the rooflight; the full strength and indeed, any weaknesses can only be determined when tested as a complete unit for both soft body and hard body impacts, and for a static load.

Contrary to British Standard’s document BS 5516-2:2004 which states that it is acceptable to provide a toughened inner pane of glass when an IGU is located no greater than 13m above the finished floor level, it is recognised that a non-laminated pane of glass is incapable of retaining a body once broken, and should therefore be considered ‘Fragile’. Xtralite also disagrees with NARMS’s recommendation that only where a specific risk has been established a laminated inner pane should be chosen, and is calling for this to be mandatory in all situations.

Alan Keiller, spokesperson for the Centre for Window and Cladding Technology commented: “CWCT provides guidance on the selection of glass for use overhead in its Technical Note 68. For sloping glazing this Technical Note permits the same options as BS 5516-2 but requires the selection to be based on a risk assessment for the particular application. In most cases the risk assessment will lead to the selection of a laminated glass.

“Where there is a risk of impact on the glass from maintenance activities, the glass should also satisfy the requirements of CWCT Technical Notes 66 and 67. In this case a suitably robust laminated glass would be required.”

With such conflicts being discussed it may be tempting to move away from the specification of glass in overhead rooflights, particularly as technology has brought alternatives to market such as polycarbonate. However, consumer and end user benefits should be considered with glass still delivering myriad of benefits for users including, but not exclusively, better acoustic properties, reduction of sound transmission and optical clarity.

Responsible specification
Nothing less than a change in industry standards will ensure the safety of those that pass under, and those that work on roofs around rooflights. Safety should always be paramount when rooflights are specified, and whilst the use of toughened and laminated delivers a marginal cost increase, we believe the cost is negligible in comparison to public safety. We would also welcome a comment from British Standards as to where they stand with regards our findings and if they feel there should be a rise to the minimum standard required for overhead glazing.