"Anti-burglary" is not a product feature, it is a test class. BS EN 356 defines eight of them: P1A to P5A by dropping a 4.110 kg steel ball from 1.5 m to 9 m, P6B to P8B by hammer and axe attack up to 71 blows and beyond. The class you write into a specification is not picked by feel, it follows from the resistance class of the complete unit under BS EN 1627: RC 2 calls for P4A, RC 3 for P5A, RC 4 for P6B. And in England, Approved Document Q sets the floor at class P1A for the glazing that would let an intruder reach the lock. Thermally, laminating is paid for in kilograms, around 10 kg/m² more than 4 mm float, which the rebate and the hinges have to take.
The eight BS EN 356 classes, and the two tests that split them
Group A: the ball drop, five levels
BS EN 356 drops a steel ball of 4.110 kg and 100 mm diameter onto a 1 100 × 900 mm specimen, at impact points laid out in a triangle. The class is reached when the ball fails to pass through after the prescribed number of impacts.
| Class | Drop height | Impacts |
|---|---|---|
| P1A | 1 500 mm | 3 |
| P2A | 3 000 mm | 3 |
| P3A | 6 000 mm | 3 |
| P4A | 9 000 mm | 3 |
| P5A | 9 000 mm | 9 |
Note the step between P4A and P5A: same height, three times the impacts. What is being measured is no longer resistance to one blow but resistance to persistence.
Group B: hammer and axe, three levels
Past P5A the ball no longer discriminates. The test becomes a mechanised attack: the pane is pre-broken with hammer blows at the twelve points marking out a 400 × 400 mm square, then struck with an axe until an opening is made through that square. The class is the number of blows taken without the opening being achieved: 30 to 50 for P6B, 51 to 70 for P7B, 71 and above for P8B.
What the class does not tell you
The standard itself warns that the resistance categories are tied to no particular application: the choice belongs to the user, case by case. The regulatory floor comes from elsewhere. Approved Document Q sets it in England, and the classes above it are a commercial and insurance conversation, backed by what you wrote on the quotation and by the manufacturer's declaration of performance.
From BS EN 356 to BS EN 1627: the class that makes sense on a quotation
The glazing each resistance class calls for
BS EN 356 tests a pane on its own. BS EN 1627 tests the assembly, frame, sash, hardware and infill together, and it is the one that produces the RC class a client writes into a brief. Each RC class calls for a minimum glazing level.
| BS EN 1627 class | Minimum BS EN 356 glazing | Resistance time | Assumed tool set |
|---|---|---|---|
| RC 1 N | no requirement | no manual attack test | bodily force, small tools |
| RC 2 N | no requirement | 3 min | screwdrivers, pliers, timber or plastic wedges |
| RC 2 | P4A | 3 min | screwdrivers, pliers, wedges, saws |
| RC 3 | P5A | 5 min | plus crowbar, hammer, hand drill |
| RC 4 | P6B | 10 min | plus sledgehammer, axe, chisels, bolt cutters |
| RC 5 | P7B | 15 min | plus power tools |
| RC 6 | P8B | 20 min | plus heavy sledgehammer, angle grinder, breaker |
The N suffix marks the classes where no BS EN 356 performance is asked of the infill: the glazing there stays ordinary glazing.
What is actually tested up to RC 4
Worth knowing before selling an RC class: up to and including RC 4, the manual attack test is carried out on the frame and the locking points, not on the glass. The glazing simply has to hold its BS EN 356 class from its own separate test. An RC 2 unit has therefore never met the axe, and a P4A pane has never been attacked in situ in its frame. That disqualifies nothing, but it explains why hardware, keeps and the number of locking points weigh at least as much as the glass in the field result.
What you record on the survey
Counting the openings to be treated goes faster from the elevations, where the AI spots the windows and doors and works out their areas. On each opening you keep, note the rebate depth available, the bead type, the condition of the hinges and the number of existing locking points. Those four lines decide whether a laminate can go into the frame in place, or whether the job becomes a full replacement.
The thermal trade-off: laminating costs kilos, not watts
Why the interlayer never shows up on the Ug
BS EN 572-1 gives soda-lime silicate glass a thermal conductivity of about 1 W/(m.K). Going from 4 mm float to an 8.8 laminate therefore adds 4 mm of glass, or 0.004 m².K/W of extra resistance. Against a sealed unit whose Ug is 1.1 W/m².K, that is a total resistance of roughly 0.91 m².K/W, so the difference sits below the rounding step of declared Ug values. The Ug is decided in the gas cavity and in the low-emissivity coating, not in the thickness of the glass, which is what the comparison between single, double and triple glazing comes down to, and it is the U-value of the complete window, frame included, that ends up on the quotation.
The real cost: surface mass
With the 2 500 kg/m³ density from BS EN 572-1, every millimetre of glass weighs 2.5 kg/m². The arithmetic is immediate.
| Infill build-up | Total glass | Weight of the glass |
|---|---|---|
| 4 mm float | 4 mm | 10 kg/m² |
| 6.4 laminate | 6 mm | 15 kg/m² |
| 8.8 laminate | 8 mm | 20 kg/m² |
| 4/16/4 sealed unit | 8 mm | 20 kg/m² |
| 8.8/16/4 sealed unit | 12 mm | 30 kg/m² |
On a 1.5 m² sash, going from 4/16/4 to 8.8/16/4 puts fifteen extra kilos on the leaf, interlayers not counted. That figure, not the Ug, decides whether the existing hinges hold, whether the sash drops within six months and whether the adjustment survives the first heating season.
Light transmittance and solar factor
The interlayers cut light transmittance and shift the solar factor slightly. The order of magnitude is small but it is not nil, and it is read off the glazing data sheet, never off a sales brochure. On a south elevation already marginal for summer comfort, check the solar factor of the complete window before settling the build-up, bearing in mind that a window's solar factor is not its glazing's g-value.
What gets recorded: marking, quotation and regulation
Marking and declared performance
Laminated glass falls under BS EN 14449 and sealed units under BS EN 1279-5, the product standards that carry the declaration of performance, and that is where the BS EN 356 class is declared. Ask for that document, not an "anti-burglary" line on an order confirmation: it is the only evidence that stands up if there is a claim and the insurer asks what level was actually fitted.
Installation decides the class
BS EN 356 says so itself: security glazing has to be installed in a frame with adequate resistance of its own, and notches or holes through the glass product are to be avoided because they degrade its resistance. A P5A pane set in too shallow a rebate, packed continuously or forced under its beads is worth no more than a properly installed P2A. Setting blocks, edge clearance and drainage follow the rules of any sealed unit, and the glazing seal remains the detail where the manufacturer's warranty and the weathertightness are lost.
Approved Document Q: where the class becomes a requirement
Requirement Q1 applies to easily accessible doors and windows giving access into a dwelling. Approved Document Q defines easily accessible as any part within 2 m vertically of an accessible level surface such as the ground or an access balcony, or within 2 m of a flat or sloping roof pitched under 30° that is itself within 3.5 m of ground level. Ground floor, basement and other easily accessible windows must be secure windows tested to PAS 24, and in the Appendix B route for doorsets, any glazing that would let someone put a hand through and release the lock has to be at least class P1A to BS EN 356, with only one pane of a double or triple unit needing to reach that class. Everything above P1A is a client decision, not a Building Regulations one, which is where the arbitration between full replacement and a glass-only swap is settled.
