Glazing Regulations: Safety Glass, Critical Locations & Part N/Part K

Summary

Glazing safety regulations exist because impact with glass is a leading cause of serious lacerations and fatalities in domestic settings. The injuries sustained when a person falls against or walks through ordinary annealed glass — which shatters into large, sharp shards — can be catastrophic. Safety glass either breaks into small, relatively harmless fragments (toughened) or remains largely intact when cracked (laminated).

The requirements are set out in Building Regulations Approved Document K (Protection from falling, collision and impact), which absorbed the former Approved Document N (Glazing) in the 2013 revision. Compliance is not optional — buildings with glazing in critical locations that do not use safety glass are non-compliant with Building Regulations and present a real liability risk.

A common misconception is that double glazing provides adequate protection in all locations. It does not. Ordinary double glazed units in critical locations must use toughened or laminated glass in the inner pane at minimum, and should ideally use it in both panes. The 'A' rating on an energy-efficient window has no bearing on whether the glazing is safety-compliant in terms of impact resistance.

Key Facts

• Approved Document K (2013) — current regulation covering glazing safety (incorporated former Part N)
• BS EN 12600 — impact test method and classification for safety glass; Class 1B1 or 1C1 is toughened; Class 2B2 is laminated
• Critical locations — specified in Diagram 10 of Part K; include doors, side panels, low-level glazing, and staircase glazing
• Toughened glass — 4–5× stronger than annealed; breaks into small blunt fragments; cannot be cut after toughening
• Laminated glass — two panes bonded with PVB interlayer; cracks but stays in frame; better security and acoustic performance
• Wired glass — NOT safety glass despite historical assumption; wire reinforces against thermal shock only; breaks into large laceration-causing pieces; should not be used in new critical locations
• Safety glazing logo — kite mark or manufacturer's mark should appear on each pane; verify on glazing specification sheets
• Minimum thickness — toughened: 4mm minimum; laminated: 6.4mm minimum (3mm + 0.4mm interlayer + 3mm)
• Manifestation — large areas of transparent glazing in public/commercial areas require manifestation marks (at 850–1000mm and 1400–1600mm heights) to prevent people walking into them
• Overhead glazing — glass in roofs and overhead positions must be laminated (not toughened — risk of falling fragments); BS 5516 Parts 1 and 2 apply
• Fire-rated glazing — separate product category; meets BS EN 1364; toughened alone does not provide fire resistance

Quick Reference Table

Detailed Guidance

Identifying Critical Locations in Practice

Approved Document K Diagram 10 illustrates the critical locations, but on site the practical test is:

Doors and side panels:

• Any glazed panel within a door leaf (whether full-pane or partial) where the lowest point of the glass is below 1,500mm from the floor
• Side panels: any glass pane that is within 300mm horizontally of the door edge AND in the same plane as the door. The 300mm is measured from the nearest edge of the door frame, not the door itself.

Low-level glazing (the 800mm/900mm rule): The critical zone is determined by two criteria:

1. Does the bottom edge of the glazed panel fall within 800mm of the floor level?
2. Is the pane wider than 900mm, OR does the bottom edge fall within 300mm of the floor?

If either condition 2a or 2b is met alongside condition 1, the glass must be safety glass.

Staircase glazing: Any glazed balustrading, glass panels at the side of stairs, or glazing adjacent to a staircase where a person could fall against it must be safety glass. This includes glass balustrade panels that are fashionable in modern interior design — these must be structural glass or toughened safety glass and must meet the structural requirements for barriers under Part K.

Atria and large glazed areas: In commercial or public settings, large glazed areas visible to pedestrians at walking level must have manifestation (visible markings) to prevent people walking into the glass. Two horizontal bands: one at 850–1,000mm above floor, one at 1,400–1,600mm above floor. Each band minimum 50mm high with contrasting marks minimum 150mm wide. This is a commercial/public building requirement but applies in any larger domestic or commercial glazed area.

Glass Specification for Common Applications

Patio doors (sliding or bifold): All glass in patio door systems is in a critical location. Use toughened safety glass (minimum 6mm toughened in double glazed units for bifolds; 5mm in standard patio door leaves). Check that the inner pane of a double glazed unit is also toughened — some budget systems only toughen the outer pane.

Shower enclosures: All glass in shower enclosures is in a critical location (person impact possible). Must be toughened safety glass, minimum 6mm toughened. Tempered glass with a kite mark is standard in all reputable enclosures — verify before installing budget imported units.

Glass balustrading: Must be structural glass capable of withstanding the line load and point loads in BS 6180 (barriers in and around buildings). Typically 12mm toughened, 12.8mm laminated, or 17.5mm toughened laminated depending on height and loading. A structural engineer should specify the glass thickness for balustrading on stairs or at edge of elevated areas.

Bathroom windows: If the window is above 800mm from the floor and no part is within 300mm of a door, ordinary glass may be used. However, if any part falls within the critical zone, safety glass is required even though the window may be in an obscure/patterned specification. Always use toughened obscure glass in bathroom windows to future-proof against furniture rearrangement.

Roof glazing (rooflights, glass roofs): Laminated glass is mandatory for all overhead glazing. If the inner pane of a double-glazed rooflight unit breaks, it must not fall as shards onto occupants below. Toughened glass in overhead positions, while permitted under Part K in some historic interpretations, fails in a way that produces large dangerous shards and is not recommended. All reputable rooflight manufacturers use laminated inner panes as standard.

Replacement Glass in Existing Critical Locations

When replacing glass in windows or doors, even on a like-for-like basis, the replacement must comply with current Building Regulations. This means:

• If the existing window has ordinary glass and is in a critical location, the replacement must be safety glass
• You cannot replace like-for-like with ordinary glass and claim compliance
• This applies even to repairs — if you are fitting a new pane because the old one broke, the new pane in a critical location must be safety glass

As a FENSA-registered installer, you are responsible for ensuring all glazing in critical locations is compliant when replacing windows.

Manifestation Requirements for Commercial and Public Buildings

In non-domestic settings (commercial buildings, schools, offices, common areas of flats), large areas of glazing that could be confused with open spaces or walkways must be marked with permanent manifestation:

• Horizontal patterned or coloured bands or markers
• First band: 850–1,000mm above floor level
• Second band: 1,400–1,600mm above floor level
• Each band: minimum 50mm deep; marks at maximum 150mm intervals (e.g., dots, lines, logo marks)
• Must be visible from both sides
• Must have appropriate contrast with the background (not transparent markings)

This requirement does not typically apply to private dwellings but does apply in the common areas of blocks of flats.

Frequently Asked Questions

Does the glass in a conservatory need to be safety glass?

Yes, in critical locations within the conservatory. The same rules apply: glazed doors, low-level side panels, and any glass in the 800mm zone from the floor must be safety glass. The roof glass must be laminated (as overhead glazing). Polycarbonate roofing (common in older conservatories) is acceptable as an alternative to glass in roofing positions. The walls of a conservatory in the critical zones must also comply — standard annealed glass is not acceptable in critical wall glazing.

What about Georgian wired glass in a school corridor fire door?

Wired glass is explicitly not classified as safety glass under BS EN 12600. Its wire reinforcement prevents thermal cracking but does not prevent impact-injury laceration. In existing buildings, wired glass in fire doors is a legacy situation that is being phased out. In new works, wired glass must not be specified in critical locations. It should be replaced with fire-resistant safety glass (Pyroguard, Pyrodur, or similar) which meets both the fire resistance and impact safety requirements. This is particularly important in schools, where the Regulatory Reform (Fire Safety) Order requires periodic review of glazing standards.

How do I identify if glass is toughened?

Look for: a permanent kite mark etched or sandblasted into a corner of the pane; an acid-etched manufacturer's mark. If no mark is visible, the glass may be original annealed glass. In genuinely historic buildings, some Victorian and Edwardian glass is identifiable by its hand-made waviness; this is definitely not safety glass. When in doubt, assume the glass is not safety glass and replace if it is in a critical location.

Is there a minimum glass thickness requirement?

Part K does not set a minimum thickness — it specifies performance through BS EN 12600 classification. However, glass must be adequate for the wind loading and thermal stresses it will experience. Manufacturers' minimum thicknesses for each application (span, loading, aspect ratio) apply. As a practical guide: 4mm minimum for toughened glass in most domestic applications; 6.4mm minimum for laminated; 6mm minimum toughened in double glazed units for most structural applications.

Regulations & Standards

• Building Regulations Approved Document K (2013) — protection from falling, collision and impact; covers safety glazing (replaced former Part N)

• BS EN 12600 — glass in building; pendulum test; impact test method and classification for flat glass

• BS 6206 — impact performance requirements for flat safety glass; older standard, still referenced in existing glazing

• BS 5516-1 and -2 — patent glazing; safety for overhead and walk-on glazing

• BS 6180 — barriers in and around buildings; structural glass balustrading loads

• BS EN 1364-1 — fire resistance tests for non-load bearing elements; fire-resistant glazing

• Workplace (Health, Safety and Welfare) Regulations 1992 — Regulation 14: glazing in workplace; manifestation requirements

• Approved Document K (2013) — current Building Regulations guidance

• Glass and Glazing Federation: Safety Glazing Guide — GGF guidance on critical locations and compliance

• Pilkington: Safety Glass Applications — manufacturer technical reference

• British Standards Institution: BS EN 12600 — impact test classification standard

• window types — window types, U-values, and Part L compliance

• bifold doors — glazing requirements in bifold installations

• fire doors — fire-rated glazing in fire doors

• waterproofing — wet room considerations adjacent to glazing