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Glazed Balustrades

• Introduction
• Statutory guidance
• Toughened glass or laminated glass?
• Specification

Introduction

• The selection and specification of the appropriate glass for use in balustrade systems is not straightforward. There is a wealth of legislation, some contradictory and some just confusing. There is also the perennial question of whether to use toughened or laminated glass.
• This page, re-written in April 2011 following the publication of BS 6180:2011, seeks to provide some basic guidance to assist in the decision-making process. It must not be taken as an authoritative statement on the subject. A brief summary of the most significant changes is available, as a PDF file, from this link.

Statutory guidance

Legislation - England and Wales

Remember that following the Approved Documents is the easiest way to comply with the Building Regulations, but it is not the only way - see Use of Guidance.

• Approved Document K : The first key legislative document, referring to the design of "Guards and Barriers", is Approved Document K, Section 3, paragraph 3.2. This paragraph refers to British Standards BS 6180:1995 (now replaced by BS 6180:2011) and BS 6399-1:1996 (now withdrawn) and compliance with these standards is therefore mandatory if the requirements of Approved Document K are being followed. The "horizontal force(s) given in BS 6399-1:1996" are now incorporated in BS 6180:2011, Table 2, and it is therefore reasonable to assume that compliance with BS 6180:2011 will satisfy the requirements of Approved Document K.
• Approved Document N : The second key legislative document, referring to the safety aspects of glazing, is Approved Document N. This, in turn, invokes British Standard BS 6206:1982. BS 6206 is partially superceded by BS EN 12600, although the two standards are not directly comparable. Read the Safety Glass page.

British Standards

Remember that compliance with British Standards is not mandatory unless invoked by legislation. In this case, the standards listed below are invoked by the Approved Documents listed above.

• BS 6180:2011 : Barriers in and about buildings - Code of practice.
  For glazed balustrades the most relevant parts of this Standard are:
• Clause 6 : Design criteria:
  Clause 6.3.1 : Invokes the loading design criteria in Table 2.
  Clause 6.4.1 : Specifies a maximum deflection of 25mm under load.
• Clause 8 : This is key reading for those designing glass balustrades, particularly:
  Clause 8.1.2 : Provides definitions for three types of "barrier incorporating glass".
  Clause 8.2.1 : Provides some guidance on the appropriate use of toughened and laminated glass. Note the requirement, new in the 2011 version , that the "selection of glass should include consideration of the post-breakage behaviour". Read the paragraph on Safety below.
  Clause 8.4 : Provides design criteria for four different methods of attaching glazed infill panels.
  Clause 8.4.5 : Requires the use of toughened glass where the glass is supported by bolted connections through holes in the glass.
  Clause 8.6.3.2.2 : Specifies the required impact class, to BS EN 12600, for specific situations.
• BS 6206:1982 : Impact performance requirements for flat safety glass and safety plastics for use in buildings.
  BS EN 12600:2002 : Glass in building - Pendulum test - Impact test method and classification for flat glass.
  BS EN 12600 effectively replaces BS 6206 although the two standards are not directly comparable. Read the Safety Glass page. Neither Standard specifies the situations where safety glass is required, nor which Classes are appropriate in which situation. This is covered, primarily, in Approved Document N although this refers only to BS 6206.

Toughened glass or laminated glass?

This section must be read in conjunction with BS 6180:2011, clause 8, which provides the definitive guidance.

Strength

• BS 6180:2011 Table 2 is NOT the same as BS 6180:1999 Table 2.
• BS 6180:1999,Table 2, (now withdrawn) tabulated the maximum area of glass (by type and thickness) for three combinations of load. The two "lowest" load combinations are equivalent to the 0.36/0.5/0.25 and 0.74/1.0/0.5 values in BS 6180:2011 Table 2. The withdrawn table showed that, at these loads, there is very little difference in strength between toughened and laminated glass of the same thickness.
• At the "highest" of the three load combinations in the withdrawn table (less stringent than the 1.5/1.5/1.5 values in BS 6180:2011 Table 2), toughened glass is shown to be significantly stronger than laminated glass of the same thickness and toughened glass has, historically, been considered the default option in these locations.

Safety

• As far can be determined, there is no statutory requirement covering safety after a glass barrier has failed. The Building Regulations do not cover the situation of broken glass falling from high level and injuring those below. The Building Regulations do not cover the situation of appropriately-designed-and-installed glass in a balustrade breaking and thus leaving the area unguarded.
• The only exception is the specific situation covered in BS 6180 clause 8.5.2 (the handrail at the top of a "free-standing glass protective barrier") which covers the design of the handrail when a glass panel has fractured.
• The situation has been complicated by the addition, in BS 6180:2011, of the statement "The selection of glass should include consideration of the post-breakage behaviour." to clause 8.2.1. This apparently innocuous addition could have far-reaching implications as there is still a great deal of debate about the relative merits of different types of glass when considering their post-breakage behaviour.
• The obvious solution would appear to be to specify Laminated Glass, comprised of two panes of annealed glass. This retains its shape when broken and would thus stay in place if appropriately fixed. BS 6180:2011 clause 8.4.5 does, however, require the use of toughened glass where the infill panel is designed with bolted connections.

Guidance

• Specifiers should consider whether they wish to control the choice of toughened or laminated glass in situations where both will meet the other design criteria.
• Toughened glass may be significantly cheaper than laminated glass at the higher design loads.
• Laminated glass must be fixed in such a way that it is held securely when broken - large sheets of laminated glass falling on those below are a significant safety hazard.
• Consideration should be given to the use of laminated glass comprised of two or more sheets of toughened glass, or a combination of toughened glass and annealed glass. This will probably be the most expensive option, but may also be the option which covers all the criteria (statutory and subjective) most effectively.

Specification

Prescriptive specification

• Strength : Now that BS 6180:1999 Table 2 has been withdrawn, specifiers should be wary of specifying the glass type and thicknesses for any glazed balustrade, even if this information has been provided by a glass manufacturer. Performance specification is always the safer option for the designer.
• Safety : Specifiers should consider whether they wish to control the choice of toughened or laminated glass, or allow either if both glass types/thicknesses/sizes meet the strength criteria.

Performance specification

• Strength : It will generally be adequate to specify the minimum horizontal imposed loads from BS 6180:2011 Table 2. In clause L30/110, the NBS adopts the even more minimalist approach of specifying only the activity/occupancy category (by reference to the now withdrawn BS 6399-1), but this ignores the options within each type of occupancy and is not recommended.
• Safety : Specifiers should consider whether they wish to control the choice of toughened or laminated glass, or leave this to the person or company with the ultimate design responsibility.

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