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Glazed Balustrades
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 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.
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 and BS 6399-1 and compliance with these standards is therefore mandatory if the requirements of Approved Document K are being followed.
- 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.
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 : Barriers in and about buildings - Code of practice : For glazed balustrading the most relevant parts of this Standard are:
- Clause 6 - Design criteria (page 4) :
Clause 6.3.1 : Invokes BS 6399-1 and the loading design criteria referred to below (BS 6399-1 Table 4).
Clause 6.4.1 : Specifies a maximum deflection of 25mm under load. - Clause 8 - Glass (page 7) : 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.
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 6206, for specific situations.
Table 2 : Provides a selection of "deemed to satisfy" glass thicknesses and sizes for three sets of design criteria*. - BS 6206 : Impact performance requirements for flat safety glass and safety plastics for use in buildings : This standard sets out the criteria for "safety glass" in three categories - Classes A, B, and C (where A is the "best"). It does not specify the situations where "safety glass" is required, nor which Classes are appropriate in which situation. This is covered, primarily, in Approved Document N.
- BS 6399-1 : Loading for buildings - Part 1: Code of practice for dead and imposed loads : For glazed balustrading the most relevant part of this Standard is Clause 10 (page 7) which invokes Table 4 (page 9). Table 4 gives the required loading design criteria for different types of building occupancy.
* Note: The clear intention is that the three sets of design criteria in BS 6180 Table 2 should replicate the criteria in BS 6399-1 Table 4, and this is the case for BS 6180:1995 (no longer current). It would seem self-evident that the slightly different figures in one of the criteria in BS 6180:1999 are a "typo" but specifiers should confirm this interpretation with the Building Control Officer before relying on the sizes and thicknesses given in Table 2 of BS 6180:1999.
Toughened glass or laminated glass?
This section must be read in conjunction with BS 6180, clause 8, which provides the definitive guidance.
Strength
Refer to BS 6180 Table 2:
- At the "lowest two" of the three design criteria in Table 2 there is very little difference in strength between toughened and laminated glass of the same thickness.
- At the "highest" of the three design criteria in Table 2, which includes many of the typical situations where glazed balustrading may be used (see BS 6399-1 Table 4), toughened glass is significantly stronger than laminated glass of the same thickness and toughened glass has, historically, been considered the default option in these locations.
- The original research, which lead to the eventual publication of this page, was started when specifiers questioned whether toughened glass was really the most appropriate choice in these locations - see Safety below.
Safety
- As far can be determined, there is no statutory guidance 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 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 clause 8.4.5 does, however, require the use of toughened glass when 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 : The only definitive published information is BS 6180 Table 2, and this only covers fully framed single glass pane infill panels. Specifiers should be wary of taking design responsibility for specifying the glass types and thicknesses for two-edge framed infill panels, clipped infill panels, and bolt-fixed infill panels, based solely on glass information provided by glass manufacturers. Performance specification is always the safer option, for the designer, if the glass infill panels are not fully framed.
- 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 should generally be adequate to specify the minimum horizontal loads from BS 6399-1 Table 4. In clause L30/110, the NBS adopts the even more minimalist approach of specifying only the activity/occupancy category, but this ignores the options within each category and is not recommended.
- Note: Barriers covered by BS 6399-1 Table 4, occupancy type C5 (xi) - which include most areas of "public assembly", including shopping malls - must be specified by performance as the required loads are outside those covered by BS 6180 Table 2. Specifiers should be wary of taking design responsibility for the complete barrier installation relying solely on the glass information provided by glass manufacturers.
- 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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