The Non-Fragile topic is of great importance nowadays as everyone becomes more aware of the health and safety issues on building sites and the need to safeguard people working there.

Safety concerns with rooflights - the Non-Fragile issue

Whilst recognising that achieving natural daylight in buildings through the use of rooflights is important, falls through fragile roofs and rooflights has been identified as one of the main causes of numerous deaths and thousands of injuries that have occurred in the construction industry over the years. The statistics were sufficiently alarming for the Construction Division of the Health & Safety Executive (HSE) to single out fragile roofs for a priority programme in 2004/5.

Rooflights are a particularly obvious element of a roof assembly that should be able to support the instantaneous loads imposed by persons stumbling or falling onto them.

The HSE are extremely keen to have non-fragile assemblies specified for installation on roofs, especially in buildings that are considered to be at risk from vandals/intruders who find their way on to the roof.

However, there is sometimes a misunderstanding regarding the safety of people on roofs. Some specifiers think that by requesting a roof glazing system that conforms to BS6206 then they are providing a safe rooflight. This is not the case.

The HSE Document HSG33 outlined the Health & Safety recommended testing method ACR[M]001:2019 ‘Test for Non-Fragility of Profiled Sheeting Roofing Assemblies’. The ACR[M] drop test is far more onerous than BS 6206 as it represents a human impact incident on a roof surface where a fall through (the glazing) might result in death or serious injury, whereas BS 6206 was designed for vertical low level glazing where the main objective is to prevent human injury from broken glass.

ACR[M]001:2019 is a test of an assembly rather than a product. Rooflights are not tested alone, but as part of a representative roof assembly and it is the whole assembly which achieves non-fragility.

The Advisory Committee for Roofwork, led by the Health & Safety Executive, undertook research that led to the development of the above test, which represents a human impact incident on a roof surface.

The pass categories than can be achieved with the ACR[M] test are shown below:

  • 'A' is the highest rating and is achieved only if there is no visible or significant damage to the whole assembly after multiple drops.
  • The 'B' classification is based on minimal damage caused by multiple drops.
  • A 'C' graded pass requires only one drop test with the impactor.

The Twinfix Multi-Link-Panel NF

The Multi-Link-Panel NF (Non-Fragile) combines a maintenance-free aluminium frame fitted with virtually unbreakable polycarbonate glazing, either multiwall or solid.

Many years ago we build a test rig in accordance with the HSE’s requirements and we regularly assess our Multi-Link-Panel NF products to the ACR[M] test. Every Multi-Link-Panel NF polycarbonate option we offer has achieved a 'B' pass rating.

In addition, we have tested 16mm multiwall polycarbonate fitted into one of our own glazing bar systems. This failed the test, with the multiwall sheet simply popping out of the 60mm wide glazing bars. This demonstrates the wisdom of the HSE requirement to carry out the test on 'assemblies' and not on individual components.

We have also tested 6.8mm laminated glass. It failed, with the 45kg impactor bag crashing straight through the glazing, leaving a huge hole.

HSE Drop Test Videos

Please click on the link below to see the HSE drop tests carried out on a range of relevant products.

CDM Regulations

The CDM regulations state that designers must:

“when carrying out design work, avoid foreseeable risks to those involved in the construction and future use of the structure. In doing so, they should eliminate hazards (so far as is reasonably practicable, taking account of other design considerations) and reduce risk associated with those hazards which remain”

Help & Advice

If you have a project in mind or would like help or advice on any of our products or services, please either ring us on 01925 811311, email us at or get in touch via the enquiry form on our Contact Us page.


Related Downloads

FilenameFile TypeSize
HSG33 Appendix 4 Fragility.pdf  HSG33 Appendix 4 Fragility.pdfPDF254 KB
ACR article on non-fragile roofs May14.pdf  ACR article on non-fragile roofs May14.pdfPDF126 KB

Related FAQs

1. Can you walk on polycarbonate sheet?
Polycarbonate has been tested against UK wind and snow loads and we can supply you with recommended glazing centres for each thickness of polycarbonate. However you should never walk directly on polycarbonate sheet. A crawling board or similar should be placed across at least two structural supports of the roof. We can manufacture aluminium framed polycarbonate panels which have been tested for non-fragility to ACR[M]001:2019 – this does not mean you can walk on the polycarbonate but gives added resistance to accidental falls.
2. Am I required by the Building Regulations to have a non-fragile roof?
The Building Regulations themselves do not refer to “non-fragility” in relation to roofing systems. However, they do require that any structure is designed in accordance with the CDM Regulations, (Construction Design & Management) and these Regulations require that all buildings should be designed to utilise the safest method of construction available. (i.e. if a non-fragile design is feasible, then it should be used.)
3. Polycarbonate is virtually unbreakable, so isn't polycarbonate glazing non-fragile?
No, in many canopies that use multi-wall or solid polycarbonate glazing, the glazing is simply clamped into a glazing bar system that just holds these sheets in place. Whilst the sheet itself might not break, a falling object, (and in some cases even a strong wind), can flex the sheet and force it out from between the glazing bars. If someone were to trip on such a roof, they could fall through, endangering themselves and anyone underneath. Remember..... just because it doesn't break doesn't make it non-fragile.