Fragile industrial rooflight replacement is the only permanent answer to an aged in-plane sheet that will no longer arrest a fall. A rooflight becomes fragile because ultraviolet light breaks down the polyester resin holding the glass fibres together, and the sheet loses the toughness that once let it stop a falling person. Nothing restores that. Coatings do not, overlays do not, and a visual glance from the floor cannot tell you how far gone a sheet is. What resolves it is a competent fragility assessment followed by replacement with a tested non-fragile assembly, recorded against the configuration actually installed on your building.
If you already know or suspect you have a fragile rooflight and people can get onto that roof, deal with the access first. The immediate control measures, restricting access, covering or netting the opening, marking the roof plan and briefing contractors, are set out on rooflight fall through risk. Read that first, then come back to the assessment and replacement question.
Why aged in-plane sheets are the hazard they are
Falls through fragile roof surfaces remain one of the most persistent causes of death and life-changing injury in UK building maintenance work. Rooflights carry a disproportionate share of that total, and the reason is uncomfortable and simple. A degraded rooflight looks like a sound one.
In-plane rooflights sit within the roof plane, replacing a metal sheet rather than standing above it on a kerb. From below they are a bright panel in the ceiling. From above, once a roof has weathered for twenty years and everything is the same shade of grey-green with moss in the valleys, an in-plane GRP sheet and the steel sheet next to it can be hard to distinguish at a glance, particularly when the roof is wet. A person crossing a roof to reach a plant item does not read profiles. They read a continuous surface.
Underneath, the material has changed. Glass reinforced polyester starts life as fibre held in tension by a cured resin matrix, protected on the weather face by a gelcoat or a surfacing film. Once that protection is spent, ultraviolet attacks the resin. Fibres are exposed, water wicks along them into the laminate, and the sheet becomes progressively more brittle. It can still hold its own weight and shed rain for years after it has stopped being able to absorb the energy of a body landing on it. That gap between looking serviceable and being safe is where the accidents happen.
Around Ipswich, the port estates and the industrial stock along the A14 corridor, most buildings went up between the 1970s and the early 2000s in profiled metal with in-plane GRP rooflighting. Sheets specified for fifteen to twenty-five years are now thirty or more years old. That is not a prediction of failure. It is a statement that the original classification on those roofs can no longer be relied on.
Non-fragility is an assembly classification, and it expires in practice
This is the point most facilities managers have never been told, and it changes how you read every document in your building file.
The industry test for non-fragility is ACR[M]001, published by the Advisory Committee for Roofsafety. A weighted bag is dropped onto a complete rooflight assembly, installed as it would be on a real roof, at defined positions including the worst case. The assembly passes if it holds. The certificate that comes out of that test describes the whole configuration: the sheet at a stated thickness and profile, over a stated span, with a stated fixing pattern, into a stated supporting structure.
Two consequences follow, and both matter.
- The classification does not travel with the sheet. Take a sheet that passed over 1.8 metre purlin spans and install it across 2.4 metre spans and you have an untested assembly. Reduce the fixing centres, change the supporting structure, use a different washer, and the certificate on file no longer describes what is on your roof. A supplier can truthfully say a product is non-fragile to ACR[M]001 and you can still finish with a roof nobody has ever tested.
- The classification degrades with age. The test certifies the assembly when new. It says nothing about the same assembly after twenty-five years of ultraviolet exposure. A rooflight that genuinely passed on installation day is not non-fragile a quarter of a century later, because the resin that made it pass has been breaking down the entire time.
The working position across the industry follows from that: treat any rooflight as fragile unless documentation proves otherwise for the configuration actually installed, and unless the installation date is known and recent enough for the classification to still mean something. An undated rooflight of unknown origin is a fragile surface for planning purposes. That is not pessimism, it is the only defensible assumption available.
The procurement side of this, what to write into a specification, what to ask a supplier to evidence, and what should appear on the submittal, is covered in detail on non-fragile rooflight specification. This page stays with assessment and the replacement decision.
What the duty holder is actually carrying
Responsibility here is statutory, not contractual, and it does not transfer to whoever last worked on the roof.
- Health and Safety at Work etc. Act 1974. General duties on employers and on those in control of premises to ensure, so far as reasonably practicable, the health and safety of employees and of other people affected by the work, including contractors and visitors.
- Work at Height Regulations 2005. Work at height must be properly planned, appropriately supervised and carried out safely. The regulations deal explicitly with fragile surfaces. Where work near or on a fragile surface cannot be avoided, the requirement is for platforms, coverings, guard rails or similar collective protection, plus prominent warning notices at the approach to the surface.
- Construction (Design and Management) Regulations 2015. Where rooflight work is carried out, client duties bite: providing pre-construction information about known fragile surfaces, appointing duty holders, and maintaining the health and safety file. If you hold information about your roof and do not pass it on, that is a client failure regardless of who does the work.
Translated into what a facilities manager has to be able to do on any given Tuesday: say which surfaces on the roof are fragile, show where they are on a plan, communicate that to every person who goes up before they go up, and either prevent access to those areas or protect against the consequence of a fall. Buildings fail that test constantly, and usually not through negligence. They fail it because the information was never assembled and nobody inherited it.
Nobody should be walking on, kneeling on, leaning over or standing beside a suspect rooflight to work out how bad it is. Inspection is done from below, from a mobile elevating work platform, or by a competent person working from a properly protected position with fall protection in place. The material that is being assessed is the material that might not hold.
How fragility is actually assessed
An assessment is a competent person’s judgement supported by evidence, not a checklist a caretaker can run. What a competent assessment gathers, and why each item matters:
| Evidence | How it is obtained | What it tells you |
|---|---|---|
| Installation date | Building records, O and M files, sheet embossing, refurbishment history | The single strongest indicator. Age drives resin degradation more than anything else |
| Original assembly documentation | Health and safety file, original submittals, manufacturer records | Whether a classification ever existed, and for which span and fixing pattern |
| Purlin span and fixing pattern as built | Physical measurement at survey | Whether any historic certificate describes the configuration that was actually installed |
| Surface condition of the weather face | Close visual inspection from a MEWP or protected position | Fibre bloom, crazing and chalking indicate the surface protection is spent and resin loss is under way |
| Light transmission loss | Comparison from inside, measured lux beneath rooflit and unlit areas | A proxy for how far degradation has progressed across the population |
| Liner presence and condition, twin skin roofs | Internal inspection from below | The liner is what a person meets after the outer sheet. A missing or fragile liner is decisive |
| Fixing condition and washer integrity | Inspection at each position | Corroded or dished fixings mean the sheet is no longer restrained as the classification assumed |
| Access routes and working positions | Roof walk plan, plant locations, maintenance schedule | Where people actually go, which sets the priority order for anything found |
Assessment records condition and configuration. It does not re-certify an aged assembly, because ACR[M]001 is a destructive test on a new assembly and there is no field equivalent.
That last note is worth sitting with. There is no instrument that can be pointed at a thirty year old rooflight to declare it non-fragile again. Assessment tells you how confident you can be that it is fragile, and how urgently that matters given who walks where. It does not restore a classification. Only new material, correctly installed, produces a roof with a current one.
A worked assessment: a 4,800 m² distribution unit
Take a typical single-bay distribution building on a Suffolk estate. Profiled steel roof, twin skin, 4,800 m² roof area, in-plane GRP rooflights at roughly 12 per cent of roof area, 96 sheets at 3.0m x 2.0m cover. Building completed 1996. No rooflight documentation in the file.
- Age. Thirty years. Original sheets on a 1996 building were most likely basic gelcoat or early polyester film, specified for fifteen to twenty years. They are ten to fifteen years past that.
- Documentation. None. No classification exists, therefore none can be relied on.
- Configuration. Purlin spans measured at 1.9m, original fixings at crown centres, several positions with dished washers and corrosion staining.
- Condition. Widespread fibre bloom on the south-facing slope. North slope visibly better but the same age and the same material.
- Transmission. Floor readings beneath rooflit bays around 40 per cent of what the design would have delivered new.
- Access. Two roof-mounted extract units and a chiller condenser served by a walk route that crosses eleven rooflight positions with no walkway.
Outcome: the entire population is treated as fragile. Eleven positions on the maintenance walk route are phase one, alongside four positions over the pick face where a fall would land on a working floor. The remaining 81 positions go into a two-phase programme across the next two financial years, with a demarcated and signed roof walk route installed immediately as an interim control while the programme runs. Nothing about that outcome required a laboratory. It required someone competent to go and look properly, and to write it down.
The replacement specification that resolves it
Replacement is what converts an undocumented fragile roof into a documented one. The scope that achieves it, at the level a duty holder needs to check:
- Assembly specified as a whole. Sheet grade, thickness and profile, stated against the measured purlin span and a defined fixing pattern, with the ACR[M]001 classification recorded for that combination rather than for the sheet in isolation.
- Profile physically taken from the roof. Crown pitch, crown width, rib height and side lap geometry measured on site. Much pre-2000 industrial profile is out of production, and a moulded-to-match sheet is often the correct route. A near-miss profile leaks at every side lap.
- Liner rooflights on twin skin roofs. The liner is the safety-critical layer beneath the outer sheet. A non-fragile outer above a fragile or absent liner is not a resolved roof.
- Fixing grade matched to exposure. 316L stainless throughout on port-side and coastal work at Felixstowe or Harwich, where chloride pitting attacks lesser grades at exactly the points holding the assembly together. Inland estates around Stowmarket or Colchester do not carry that load and do not need the premium.
- Surfacing film chosen for the hold period. The cost difference between a basic gelcoat and a high performance surfacing film is far smaller than the difference in replacement interval. On a roof you intend to hold for twenty-five years this is the highest value decision in the specification.
- Documentation handed over. Roof plan with every position, assembly specification, classification against installed configuration, span and fixing pattern, installation date so the degradation clock has a documented start, and manufacturer declarations filed rather than mentioned.
Apex does not reseal, patch, overlay or liquid-coat rooflights, and on a fragility question the reasoning is at its strongest. A coating addresses water and leaves the laminate exactly as brittle as it was, with the added problem that the roof now looks maintained. An overlay creates a field-assembled sandwich that no test describes. Neither produces a classification, and a classification is the thing you are actually buying.
Questions duty holders ask
Our rooflights were sold as non-fragile when the building was built. Are they still?
Assume not. ACR[M]001 certifies an assembly when new, and ultraviolet degradation of the polyester resin removes the toughness the test measured. A sheet installed in the 1990s has had thirty years of that. There is also a second question: whether the certificate ever described your building, because the classification is tied to a specific span, fixing pattern and supporting structure. If either the age or the configuration is in doubt, the assembly is treated as fragile until a competent assessment says otherwise.
Can a rooflight be tested in place to prove it is still non-fragile?
No. ACR[M]001 is a destructive drop test on a complete new assembly in controlled conditions. There is no field equivalent that certifies an aged sheet on a live roof, and any attempt to load-test in place would put a person near a surface that might fail. Assessment records age, configuration, surface condition and documentation, and produces a judgement about fragility. Only new material correctly installed produces a roof with a current classification.
Who is responsible if a contractor falls through a rooflight on our building?
Responsibility is usually shared and it does not sit with one party. Under the Health and Safety at Work etc. Act 1974 those in control of premises have duties to people affected by work there. The Work at Height Regulations 2005 require fragile surface risk to be planned for and controlled. Under CDM 2015 the client must provide pre-construction information about known fragile surfaces. If you knew, or should reasonably have known, and did not record or communicate it, that is your exposure regardless of who the contractor was. A competent assessment and a maintained roof plan are the practical defence.
Can we just install a walkway and leave the rooflights alone?
A demarcated walkway is a legitimate interim control and it is often the right immediate step, because it keeps people away from the surface while a programme is planned and funded. It is not a resolution. The fragile surfaces are still there, they still need marking, recording and briefing, and anything requiring access away from the walk route still has to be planned around them. Treat a walkway as the thing that buys you a safe planning window, not as the end of the job.
Do we have to replace every rooflight at once?
No, and on a large roof it is rarely affordable or necessary. Phasing works when it is driven by risk rather than by geography: positions over walk routes, access points, plant needing regular maintenance and working floors go first. What matters is that the roof plan and fragility record are updated after each phase, so at any point you can state exactly which positions are documented and which are still outstanding. A part-finished programme with a current record is a defensible position. The same programme with no record is not.
How can we tell fragile rooflights from the metal sheets when we are up there?
Frequently you cannot, and that is exactly why the control has to be planning rather than observation. After twenty years of weathering, an in-plane GRP sheet and the steel sheet beside it can look near identical, particularly when wet or in poor light. The answer is a marked roof plan, permanent signage at every roof access point, physical demarcation of safe routes, and a briefing before anyone goes up. Nobody should be identifying rooflights by walking towards them and looking down.
What should we do about the roof today, before any programme starts?
Restrict and control roof access so nobody goes up casually, put the fragile surface question into your permit-to-work, brief every contractor and visitor before they climb, sign the access points, and get the positions onto a roof plan even a rough one. Then commission a competent assessment. The urgent-case sequence, including physically covering or netting a known failed or suspect opening from a safe position, is set out on rooflight fall through risk.
Related reading
- Commercial skylight installation for the full picture on industrial rooflight replacement, phasing and cost.
- Non-fragile rooflight specification for what to write into the procurement documents and what evidence to demand.
- GRP rooflight degradation for grading condition across a roof and understanding how far through their life your sheets are.
- Profiled metal roof rooflight replacement for the sheeting detail behind an in-plane swap.
- What non-fragile actually means and when to replace industrial rooflights for the short answers.
Get the roof assessed and priced
Send us the site, the roof area, the building use and whatever documentation exists, even if that is nothing. We arrange access with your team, survey every rooflight position, take the profile physically from the sheeting, measure the spans and produce a marked plan with a condition and fragility record against each position. That becomes a written scope priced by bay, phased to fit your capital cycle, with a fixed figure against a fixed scope.
Every installation carries a 10-year workmanship guarantee, and the installers on your roof have 25 years fitting rooflights behind them. We are not CHAS accredited and we do not hold your CDM duties, but we provide a construction phase plan, RAMS and health and safety file information for our own package.
Request a commercial rooflight survey for a site in Ipswich, Suffolk or north Essex.
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.