Safety glazing requirements catch out a lot of trade buyers — not because the rules are complicated, but because it is easy to focus on size and thickness and overlook the location. A panel that is perfectly specified for load and aesthetics can still be non-compliant if it sits in a critical location and is made from annealed float glass.
This guide covers Approved Document N in plain terms, explains which locations trigger the requirement, and sets out the practical steps for briefing a compliant order.
What is Approved Document N?
Approved Document N is the guidance document that supports Part N of the Building Regulations for England and Wales. Part N deals with glazing in buildings and covers two main requirements: the safe breakage of glass in critical locations, and the ability to open and clean windows safely.
For most trade glaziers and contractors, the relevant part is Requirement N1 — glazing in critical locations must either break safely or be robust enough not to break under normal impact. The document defines what "breaks safely" means and sets out how to demonstrate compliance.
Scotland uses Technical Handbook Section 4, and Northern Ireland uses Technical Booklet L — the principles are similar but the reference documents differ, so always check the applicable set of regulations for the project location.
Which locations are critical?
Approved Document N defines critical locations as areas where people are likely to come into contact with glazing, particularly areas that are low enough to walk into, stand against or fall through. The main categories are:
- Glazing in doors and door side panels between 1,500 mm wide that extends to within 1,500 mm of floor level
- Glazing in windows and panels where the bottom edge is within 800 mm of floor level
- Glass in shower enclosures, wet rooms, and bathroom screens
- Glass balustrades, Juliet balconies, and guarding used to prevent falls
- Internal partitions and screens where the glazed panel is adjacent to or forms a walking route
The boundary dimensions matter. A panel whose bottom edge is at 801 mm above finished floor level is outside the critical zone for Part N — but it may still be in a location where good specification practice suggests safety glass anyway.
KH Glass tip
If you are unsure whether a panel sits in a critical location, measure from the bottom edge of the glazed area to finished floor level. For bathroom glass, all enclosures and screens should be treated as critical locations regardless of height.
Which glass types comply?
Approved Document N allows three routes to compliance for glass in critical locations:
- Safe breakage: glass that, when it breaks, breaks into small, relatively harmless pieces — toughened (tempered) glass and certain laminated glasses meet this criterion
- Safe breakage with retention: laminated glass that holds together when broken, keeping large fragments in place and reducing the risk of injury
- Robustness: annealed glass that is thick and small enough that it is very unlikely to break under normal impact — but this route is rarely used in practice and has strict size limits
For most trade applications, toughened glass or toughened laminated glass is the straightforward answer. Annealed glass should not be assumed to comply simply because it is thick.
BS EN 12600 impact performance classes explained
BS EN 12600 is the European pendulum impact test for flat glass. It classifies glass on two axes: the energy level it withstands, and the way it breaks. Approved Document N references this standard as the basis for demonstrating safe breakage.
The classification uses a code like 1(B)1 or 2(C)2:
- The first number is the drop height (1 = 450 mm, 2 = 450 mm at higher energy, 3 = 1,200 mm) — a lower number means tested at higher impact
- The letter is the break type: A = small particle fracture (toughened), B = no break or retained fracture (laminated), C = large crack without collapse (annealed at limits)
- The second number is a secondary drop height confirmation
Approved Document N requires glass in critical locations to achieve Class 1(B)1 or Class 1(A)1 as a minimum. Standard toughened glass (6 mm and above) consistently achieves Class 1(A)1. Most structural laminated glass achieves 1(B)1.
What about balustrades and structural glass?
Glass balustrades are governed by an additional set of requirements beyond Part N. Because they act as guarding — protecting against falls — they must also satisfy Part K (protection from falling, collision and impact) and BS 6180, which covers barriers in and around buildings.
The key requirements for glass balustrades are:
- Glass must be toughened, laminated, or toughened laminated — annealed glass is not permitted
- The panel must be designed to carry the specified barrier load — typically 0.74 kN/m for domestic or 3 kN/m for commercial applications
- Top rail height minimums apply: 900 mm above finished floor level for most residential settings, 1,100 mm above in some commercial and public settings
- For frameless glass balustrades, the fixing system and glass thickness must be specified together — glass thickness alone does not confirm compliance
For large commercial or apartment projects, it is worth asking your structural engineer to confirm the glass and fixing specification meets both Part K and BS 6180 requirements before ordering.
KH Glass tip
KH Glass supplies toughened and laminated glass for balustrades across residential and commercial projects. All toughened glass leaves our facility with the BS EN 12150 kite mark and EN 12600 classification — confirm at order stage that you need the certification documents if they are required for the building control sign-off.
Markings and certification — what to check on delivery
Toughened glass produced in the UK must be permanently marked with the CE or UKCA mark (or both), the BS EN 12150 standard, the manufacturer's identity, the glass thickness, and the safety class. The mark is typically etched or screen-printed in a corner of the panel.
On delivery, check that:
- Every panel carries the permanent safety marking — if it is not there, the glass has not been certified to the standard
- The thickness matches the order — a 6 mm panel delivered in place of a specified 10 mm panel is a compliance issue, not just an inconvenience
- For laminated glass, the interlayer type and construction are as specified — a 6.4 mm laminate (two 3 mm panes with a PVB interlayer) behaves very differently from a 6 mm toughened panel
If your project requires a declaration of performance or test certificates for building control, ask your supplier at the quotation stage rather than waiting until after delivery. Retrospective certification is rarely straightforward.
How to brief a compliant order
The clearest orders include the information a supplier needs to check compliance at quotation stage. For safety glazing, that means:
- Glass type: toughened, laminated, or toughened laminated
- Thickness and finished size
- Application and location — door panel, balustrade, shower screen, etc.
- Any cut-outs, holes, notches or edge work required (these must be done before toughening)
- Whether certification documents are needed for building control
A common mistake is ordering a panel cut to size and then trying to drill or notch it on site. Toughened glass cannot be cut, drilled or altered after toughening — any modifications must be specified before the glass enters the furnace. If the brief changes after the glass is made, it must be re-ordered.
If you are specifying safety glazing for a trade or commercial project and want to confirm the right product and certification route, speak to KH Glass. We supply toughened and laminated glass to trade across Birmingham, the Midlands, and nationwide. View our toughened glass and balustrade pages, or get in touch for a made-to-measure quote.