Non-fragile means a complete rooflight assembly has passed a drop test showing it will arrest a person falling onto it from above. It is a tested classification of the whole assembly, the sheet plus its span and fixings, not a permanent property of the material, and it degrades with age as the sheet weathers. A sheet on its own is never non-fragile, and a rooflight that was non-fragile when installed becomes fragile as it ages.
That is the snippet version. This answer sits under our commercial skylight installation service and unpacks it for facilities managers and duty holders. It is not a substitute for a competent fragility assessment of your roof.
A tested classification, not a material property
The word “non-fragile” describes a test result, not a substance. The industry test is ACR[M]001, a drop test where a weighted bag is dropped onto a complete rooflight installed as it would be on a roof. If the assembly holds the bag, it is classified non-fragile. The classification belongs to that sheet, at that thickness and profile, over that span, with that fixing pattern, into that structure. This is why you cannot call a material non-fragile in the abstract: change the span or the fixings and the same sheet may not pass. Our non-fragile rooflight specification page covers the test in full.
It degrades with age
This is the part most often missed, and the most important for safety. A rooflight arrests a fall because the resin in the sheet holds the glass fibres in tension and lets the sheet flex and absorb the impact. Ultraviolet light breaks that resin down over decades, the sheet gets brittle, and it loses the property that made it non-fragile. It does this invisibly, ahead of any obvious surface failure. So:
- A rooflight that genuinely passed the test when installed does not stay non-fragile.
- A twenty-five year old GRP rooflight installed as non-fragile should be assumed fragile now.
- An undated rooflight of unknown origin is a fragile surface for planning purposes.
Never treat a suspect rooflight as a walking surface. Even a Class B non-fragile assembly is designed to arrest a fall, not to be walked on, and that ability fades with age. A rooflight of unknown condition is a fragile surface. Restrict access to it, work off staging or a platform that spans it, and get it assessed. Do not test a rooflight by standing on or near it.
Fragile does not mean broken
A fragile rooflight is not necessarily a damaged one. It can look sound, keep most of the rain out, and still be fragile, because embrittlement removes the load-arresting property long before the sheet visibly fails. This is exactly why fragility cannot be judged by looking up from the floor, and why the working assumption across the industry is that any rooflight is fragile unless documentation shows otherwise for that assembly at that age.
Why it matters
Falls through fragile roof materials remain one of the most consistent causes of death and serious injury in building maintenance, and rooflights are the single largest contributor, because they sit flush in a roof that otherwise looks solid and degraded ones look identical to sound ones. The duty holder for a building has to manage that risk: know which surfaces are fragile, record it, tell anyone who goes on the roof, and either prevent access or protect against a fall. “Non-fragile” is one input to that, not a clearance to forget it.
What it means around Ipswich
Across the industrial stock of Ipswich, the port estates and the wider Suffolk and north Essex estates, much of which was built between the 1970s and early 2000s, most rooflights are now old enough that any original non-fragility has degraded away. Very few buildings hold any documentation for them. On the coastal belt near Felixstowe and Harwich, chloride exposure shortens sheet life, so the degradation runs faster still. In practice this means most existing rooflights on these estates should be treated as fragile until assessed.
Is a non-fragile rooflight safe to walk on?
No. A non-fragile assembly is designed to arrest a fall, not to serve as a walking surface, and its ability to do even that degrades with age. Never treat a rooflight as a walking surface. Access across a roof is planned on staging or a platform spanning the rooflights, and suspect ones have access restricted until assessed.
Can an old rooflight still be non-fragile?
Not reliably. Non-fragility degrades as ultraviolet light breaks down the resin that lets the sheet arrest a fall, and it does so invisibly. A GRP rooflight over about twenty years old should be treated as fragile whatever it was when new. The installation date matters as much as the original classification, and an undated rooflight is treated as fragile.
Find out where your roof stands
If you cannot show a current non-fragility record for your rooflights, they should be treated as fragile. A survey replaces that assumption with a graded, documented position for every one.
Request a fragility survey. Read across to what to do about a fall-through risk now, when to replace industrial rooflights, and the non-fragile specification guide.
Thinking about this job? We survey across Ipswich, Suffolk and north Essex and give you a fixed price before any work starts, with a 10-year workmanship guarantee.