Key points
- Toughened glass is made to BS EN 12150. Laminated glass is made to BS EN 14449 (product: BS EN ISO 12543). Impact performance is classified to BS EN 12600.
- Free-standing glass with no independently supported handrail should be toughened laminated, so it stays in place if a pane breaks.
- Heat soak testing to BS EN 14179 reduces the risk of spontaneous breakage of toughened glass from nickel sulphide inclusions.
- Low-iron glass reduces the green tint. It looks better, but it does not change the strength or safety of the glass.
Glass types
- Toughened (BS EN 12150). Heat-treated so it is much stronger than ordinary annealed glass and breaks into small, blunt pieces. It cannot be cut or drilled after toughening, so all holes and notches must be made first.
- Heat-soaked toughened (BS EN 14179). Toughened glass given an extra heat test that breaks most panes with nickel sulphide inclusions before they leave the factory.
- Laminated (BS EN 14449 / BS EN ISO 12543). Two or more plies bonded with an interlayer. If one ply breaks, the pieces stay attached to the interlayer. Stiffer ionoplast interlayers hold up better after breakage than standard PVB.
Post-breakage behaviour
The structural safety body CROSS (SCOSS) has warned about glass balustrades that rely on one toughened pane. If that pane breaks, nothing is left to stop a fall. Where glass is free-standing, with no handrail that is supported independently of the glass, use toughened laminated glass so the barrier stays in place after a ply breaks. Do not rely on clamp friction alone to hold glass.
Impact safety
Glass in critical locations must meet the impact-safety rules in Approved Document K, Section 5. Critical locations include glass up to 800mm above floor level, and glass in and beside doors up to 1500mm. Impact performance is classified by the pendulum test in BS EN 12600.
Low-iron glass
Standard float glass has a green tint, which shows most at the edges and in thick laminated units. Low-iron glass has less iron oxide, so it is clearer. Choose it for appearance only. It makes no difference to strength or safety.
Fixing systems
- Base channel (glass clamped or set in a continuous channel)
- Spigots or clamps at intervals
- Standoff (bolt-through) fixings to the face of a slab or stringer
- Framed or post-and-rail, with glass as infill
Use a system with test data for the load category in our heights and loads guide. Confirm what it fixes into: concrete, steel, timber or a waterproofed terrace.
Specification checklist
- Load category and minimum height for each location
- Glass make-up (ply thickness, toughened or heat-strengthened, interlayer), confirmed by calculation
- Heat soak testing
- Handrail or top cap: required for post-breakage safety, or for appearance only?
- Low-iron or standard glass; edge finish
- Fixing system and substrate; waterproofing interfaces
- Wind exposure; access for cleaning and replacement
Sources
- CROSS (SCOSS) alert: Structural safety of glass in balustrades
- Approved Document K: protection from falling, collision and impact (2013 edition, GOV.UK)
- BS EN 12150, BS EN 14179, BS EN 14449, BS EN ISO 12543, BS EN 12600 (BSI)
- BS 6180:2011 (BSI)
General guidance only, not design advice for a specific project. Check the current edition of each document.