To specify non-fragile rooflights, ask the supplier what span and fixing pattern the ACR[M]001 classification was tested at, insist those match your roof, demand the class and the installation date in writing, and get the classification recorded against the configuration actually installed. The sheet alone is never non-fragile. The whole assembly, at your spans and fixings, carries the classification, and it degrades with age.
This answer sits under our commercial skylight installation service and gives the practical checklist. For the full detail on how the test works and the duties behind it, read our non-fragile rooflight specification knowledge page. Nothing here replaces a competent assessment of your actual roof.
![A rooflight submittal document on a desk listing an ACR[M]001 classification, span and fixing pattern, under flat overcast daylight](https://apexskylightsipswich.co.uk/wp-content/themes/apex-skylights/assets/img/gen/commercial-hero.webp)
The questions to put to a supplier
- What span was the classification tested at? It only holds up to that span. Your purlin spacing must be at or below it.
- What fixing pattern was tested? The fixings are part of the tested assembly and must be installed as tested.
- Class B or Class C? Class B arrests the drop. Class C is not a working surface. Your specification names which.
- Is this for single skin or twin skin? The two build-ups are tested and classified separately, and on a twin-skin roof the liner is the safety-critical layer.
- What is the surface film grade and its expected life? The classification degrades with the sheet, so the film grade sets how long it holds.
- Will you record the classification against my installed configuration? This is what makes the document describe your roof rather than a test rig.
Why the assembly, not the sheet, carries it
ACR[M]001 is a drop test on a complete rooflight installed as it would be on a roof. The result belongs to that sheet, at that thickness and profile, over that span, with that fixing pattern, into that structure. Widen the purlin spacing and the sheet deflects more and may fail. Space the fixings further apart and the assembly may fail, because the fixings are part of what holds it. So a supplier can truthfully say a sheet is “non-fragile to ACR[M]001” and you can still end up with a fragile roof, because that classification travelled with the test configuration and your building is not it.
The one sentence that protects you. “Record the ACR[M]001 classification against the span and fixing pattern you are actually installing on my roof.” A supplier who can do that is specifying an assembly for your building. One who only points at a sheet datasheet is describing a test rig, and the gap between the two is where a fragile roof hides behind a certificate.
The documents to demand on handover
- The assembly specification and its non-fragility classification as installed.
- The span and fixing pattern the classification was achieved against, matched to your roof.
- The installation date, so the degradation clock has a documented start.
- Manufacturer declarations for the sheet material, filed rather than mentioned.
- A roof plan marking every position, so the record is spatial and can be handed to anyone going on the roof.
Remember it degrades
Non-fragility is not permanent. Ultraviolet light breaks down the resin that lets a sheet arrest a fall, and the sheet embrittles over decades, invisibly. A rooflight specified and installed as non-fragile is fragile again by the end of its life, which is why the installation date belongs in the record and why a twenty-five year old rooflight is assumed fragile whatever its original certificate said. Our what non-fragile actually means answer puts this in plain terms, and when to replace industrial rooflights gives the age bands.
Why it matters locally
Across the Ipswich estates and the wider Suffolk and north Essex industrial stock, most buildings cannot produce any non-fragility record for their existing rooflights, which is itself the answer to whether those rooflights should be treated as fragile. On the coastal belt, chloride exposure shortens sheet life, so the degradation of the classification runs faster and the record matters even more. Specifying it properly on replacement is how you replace an unknown with a documented position.
Can I rely on a manufacturer’s non-fragile datasheet?
Only as far as it matches your roof. The datasheet describes the sheet at the span and fixings it was tested with. If your purlin spacing is wider or your fixing pattern different, the classification does not carry over. Insist the classification is recorded against the configuration installed on your building, not just quoted from the sheet datasheet.
Is a non-fragile rooflight safe to walk on?
No. A Class B assembly is designed to arrest a fall, not to be used 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 that spans the rooflights, and suspect rooflights have access to them restricted until they are assessed.
Get it specified against your roof
We specify non-fragility as an assembly, record it against your real spans and fixings, and date it so the record is complete. That is what turns an unknown roof into a documented one.
Request a survey and specification. Read across to what non-fragile means, why replace rather than patch, and the full 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.