Part K Safety Glass Rules: Where Toughened and Laminated Glass Is Mandatory

Every year in the UK, approximately 4,000 people are injured by falling into or through ordinary annealed glass in their own homes. Part K of the Building Regulations (and its equivalent, Approved Document N, which was merged into Part K in 2013) exists to reduce that number by mandating safety glazing in specific locations.

What Part K requires

Approved Document K (Protection from Falling, Collision and Impact) specifies that glazing in “critical locations” must either:

1. Break safely: The glass must either not break, or break in a way that is unlikely to cause injury (toughened glass shatters into small, relatively harmless granules)
2. Be strong enough: The glass must be able to resist a person falling against it without breaking, or
3. Be protected: A screen or barrier must shield the glass from impact

There is no option to install standard annealed glass in a critical location and rely on a “warning sticker.” The requirement is for the glass itself to meet a performance standard, or for a physical barrier to prevent impact.

Critical locations: where safety glass is mandatory

Part K defines critical locations as follows:

1. Glazing in doors and door side panels

Any glass within 1,500mm of finished floor level that is in or adjacent to a door must be safety glazing. “Adjacent” means within 300mm of the door edge — this catches narrow side panels and fanlights that homeowners sometimes leave as annealed glass.

This applies to:

• External front and back doors
• Internal doors (including sliding doors)
• French door pairs (both leaves)
• Patio sliding door panels
• Side panels and top lights within 300mm of the door

2. Low-level glazing in windows and walls

Any glass within 800mm of finished floor level in a window or internal wall must be safety glazing. This is the rule that catches out many replacements in living rooms where the bottom pane of a bay window sits below the 800mm line.

The 800mm threshold is measured from the finished floor level — including any carpet, underlay, or flooring. If you install LVT flooring that raises the floor level by 15mm, the threshold measurement changes accordingly.

3. Glazing in and adjacent to baths, showers, and swimming pools

Any glass in or adjacent to a bath, shower, or pool area must be safety glazing regardless of its height. This covers:

• Bathroom windows
• Shower screens
• Glass partitions near baths
• Pool enclosure glazing

The risk here is not just falling into the glass but slipping on a wet floor and colliding with it. Bathroom glass is a critical location even if it is 2 metres above the floor.

Toughened glass vs laminated glass

Part K accepts two types of safety glazing. They break differently and serve different purposes:

Toughened (tempered) glass

Toughened glass is heated to approximately 620°C and then rapidly cooled. This process creates surface compression that makes the glass four to five times stronger than annealed glass of the same thickness. When it does break, it shatters into small, blunt granules rather than sharp shards.

• Standard: BS EN 12150 (thermally toughened soda lime silicate glass)
• Marking: Must carry a CE/UKCA mark and the standard reference etched into a corner
• Cost premium: Approximately £15-£30 per pane over annealed glass
• Typical use: Low-level windows, door panels, bathroom glazing

Laminated glass

Laminated glass consists of two or more layers of glass with a PVB (polyvinylbutyral) or EVA interlayer. When it breaks, the interlayer holds the shards in place rather than letting them fall. The glass cracks but does not shatter out of the frame.

• Standard: BS EN 14449 (laminated glass and laminated safety glass)
• Marking: Must carry a CE/UKCA mark and the standard reference
• Cost premium: Approximately £30-£60 per pane over annealed glass
• Additional benefit: Laminated glass provides acoustic insulation and security — the interlayer resists forced entry even when one layer is broken
• Typical use: Doors where security matters, overhead glazing, areas where falling glass would be dangerous (skylights, canopies)

When to choose laminated over toughened

Part K does not distinguish between the two — both satisfy the regulation. But in practice:

Situation	Toughened is fine	Laminated is better
Low-level window	✓	Only if security is also a concern
Door panel	✓	Choose laminated for PAS 24 compliance (security)
Overhead glazing	✗ (glass would fall as granules)	✓ (interlayer holds broken glass in frame)
Rooflight	✗ (safety risk from falling glass)	✓ (mandatory for overhead glazing)
Bathroom window	✓	Only if acoustic insulation is also wanted
French door leaf	✓	Choose laminated for PAS 24 security — see back door security rating

BS 6262: the glazing selection standard

Part K refers to BS 6262 (Glazing for Buildings) for the selection of glass types by location. BS 6262 Part 4 (Safety) classifies glazing by its performance:

Class	Breakage characteristic	Typical application
Class C	Breaks safely (toughened)	Most residential critical locations
Class B	Breaks safely + impact resistant (toughened thicker)	High-traffic areas, commercial
Class A	Does not break through (laminated)	Security applications, overhead

For a standard UK residential replacement, Class C (toughened) is the minimum. Class A (laminated) is necessary only in overhead glazing or where security is a parallel requirement.

Part K and replacement windows

If you are replacing an existing window that contains annealed glass in a critical location, Part K requires you to upgrade to safety glazing. You cannot replace like-for-like with annealed glass — the regulation applies to replacements as well as new installations.

This is surprising to some homeowners, particularly in period properties where the original glass in a low-level sash window is not safety glass. Replacing a broken pane with more annealed glass in a window below 800mm is a Building Regulations breach.

Enforcement

Building Control does not proactively inspect replacement window installations. The enforcement mechanism is the self-certification scheme (FENSA or Certass) — see our FENSA vs Certass vs Building Control guide. A FENSA-registered installer will not fit annealed glass in a critical location because their certification requires compliance.

However, a non-registered installer (or a DIY replacement) could fit the wrong glass and nobody would know — until a home inspection at sale time or, worse, an accident.

Part K in Scotland, Wales, and Northern Ireland

• England: Approved Document K (since 2013, incorporating former Approved Document N)
• Wales: Approved Document K (same as England)
• Scotland: Section 4 (Safety) of the Building Standards Technical Handbook, with the same critical location definitions
• Northern Ireland: Technical Booklet K (similar provisions, with minor wording differences)

Common scenarios that catch people out

The bay window bottom pane

A 1930s semi with a square bay window often has the bottom pane sitting below 800mm. The original glass is annealed. When you replace the window, the bottom pane must be toughened. Many homeowners do not realise this until the installer specifies it and the price increases by £30-£60 for the toughened pane.

The door top light

A top light (glass above the door) within 300mm of the door edge is a critical location. If your front door has a narrow glass panel above it, that panel must be safety glass even though it is well above head height. The rule is based on proximity to the door, not height.

The staircase window

A window on a stairwell landing at first-floor level has glass below 800mm from the landing floor. It must be safety glass — the same rule as any low-level window. But because staircase windows are often original and narrow, the replacement cost with toughened glass is disproportionate. Budget £200-£400 for a toughened stairwell pane in a period property.

The shower screen

A frameless glass shower screen does not fall under Part K unless it forms part of a window. However, BS EN 12150 (toughened glass) is effectively mandatory for all shower screens because manufacturers will not supply annealed glass for wet-area applications due to product liability. If you are replacing a shower screen, ensure it is toughened — the cost difference is negligible.

The Kitemark and how to verify

Safety glass must carry a permanent mark indicating the standard it was manufactured to. Look for:

• BS EN 12150 (toughened) or BS EN 14449 (laminated) etched in a corner
• CE mark or UKCA mark
• The manufacturer’s name or logo

If safety glass is installed but not marked, it does not comply — the mark is the proof. A reputable installer will show you the mark before fitting the pane.

Summary

• Part K requires safety glazing (toughened or laminated) in all critical locations
• Critical locations: door glass, side panels within 300mm of a door, windows within 800mm of the floor, bathroom glazing
• Toughened glass is the minimum; laminated glass is required for overhead glazing and recommended for security
• Replacing annealed glass in a critical location with more annealed glass is a Building Regulations breach
• All safety glass must carry a BS EN 12150 or BS EN 14449 mark
• The cost premium is modest: £15-£30 per pane for toughened, £30-£60 for laminated