What is ACR M 001?

The full title is the Test for Non-Fragility of Large Element Roofing Assemblies, and it is published by the Advisory Committee for Roofsafety. The Health and Safety Executive points to it as the recognised way of demonstrating that a roof, or a rooflight set into that roof, will hold a person who slips, stumbles or falls onto it. If you are specifying or buying rooflights for a factory, warehouse, school or any other building where someone might one day stand on the roof, this is the number that governs the safety side of the choice.

The method is a physical drop test, not a calculation. A 45kg bag, made to a defined shape and filling so that it behaves like a falling body, is dropped onto the assembly from a specified height. The point is to reproduce the load of a person who has lost their footing and landed on the rooflight, rather than someone standing on it carefully.

Two things about the method matter more than people expect. The first is that it tests the whole assembly, not just the sheet of plastic or glass. The rooflight, its fixings, the spacing of those fixings and the way it sits on the supporting structure are all part of what gets dropped on, because a unit that is strong in isolation can still tear out of a weak fixing pattern and let a body through. The second is that a pass is about retaining the person, not about the rooflight surviving undamaged. The unit is allowed to crack, deform and be written off. What it must not do is open up and let the bag fall through to the floor below.

There is a staged element to it as well. The assembly has to take the initial impact and then a second load, so that a rooflight which holds for a moment and then gives way is caught out rather than passed. This is why a genuine ACR[M]001 result always refers to a tested build-up, with stated fixings and spans, and not to a material in the abstract.

The test sorts assemblies into classes rather than a simple pass or fail. In plain terms:

• Non-fragile Class A is the most demanding grade, achieved by passing the drop test at the greatest severity. It is the highest level of assurance the test offers.
• Non-fragile Class B passes at a lower severity than Class A. It is commonly written into specifications as the working minimum for a roof assembly that people may need to access.
• Non-fragile Class C is the lowest of the three passing grades.
• Fragile is anything that does not achieve one of those three. On a roof, fragile is not a mild warning. It means the surface will not stop a fall.

As general guidance, a specifier writing a rooflight schedule for a building with any prospect of roof access will usually call for Class B non-fragility as a baseline and consider Class A where the risk is higher or the roof will be walked regularly. The right class for your building is a matter for whoever is assessing the roof access risk, so treat this as background and confirm the requirement with your designer or a competent roofing specialist rather than reading it off a page.

Falls through rooflights are one of the more common ways people are killed and injured on industrial roofs. A rooflight often looks like part of the roof and carries no obvious warning, so someone crossing the roof treats it as solid decking when it is not. That is the whole reason the test exists and the reason non-fragility is written into so many roofing specifications.

There is a second trap that catches older buildings in particular. Non-fragility is not permanent. Many rooflights are made from GRP or polycarbonate, and those materials weaken as the surface degrades under years of sunlight. A rooflight that was genuinely non-fragile when it was fitted can drift into being fragile with age, which is why any rooflight of unknown age or origin is generally assumed to be fragile until proven otherwise. If you are looking at tired rooflights on a commercial roof, replacing them with a current tested assembly is often the honest answer, and swapping a failed or degraded unit for a new one that carries a proper ACR[M]001 classification is exactly the kind of work covered by our commercial skylight installation service. The same thinking applies when you are choosing polycarbonate rooflights from scratch: ask what class the assembly was tested to and how the manufacturer expects it to age.

ACR[M]001 answers one question, which is whether the roof will hold a person. It says nothing about how the rooflight performs in daylight or in summer, and on a south-facing commercial roof those questions do not go away just because the safety box is ticked. A large area of rooflight over a warehouse or a workshop that faces south across the estuary can turn the space below into a hot box in July, so the sensible specification looks at the non-fragility class and the thermal and solar performance together.

Two other regulatory points sit alongside the test and often get muddled with it. New or enlarged rooflights are notifiable under Building Regulations, with Part L covering thermal performance and Part K covering safety glazing and guarding. Those are separate requirements from non-fragility, and a rooflight can satisfy one without satisfying the others. On a heavily glazed south-facing roof it is worth reading the solar side properly, which is the subject of our energy-efficient skylight installation work, so that the finished roof is safe to walk on and comfortable to work under rather than only the first of the two.

If you are buying rooflights for a commercial roof, ask the supplier for the ACR[M]001 test result in writing, and check three things on it: the class awarded, the exact assembly it was tested as, including fixings and spans, and the date, because an old certificate for a product that has since changed is worth little. Make sure the class matches what your roof access risk assessment calls for rather than accepting whatever is in stock.

If your existing rooflights are old, cracked or simply of unknown origin, treat them as fragile until you have evidence otherwise, keep people away from them, and plan a replacement rather than hoping they hold. A roofer is the right first call if the surrounding roof covering has failed, but where the job is swapping tired or failed rooflights for new tested units, that is our work. Tell us the roof orientation, the rough opening sizes and the class you need, and we will come back with a specification and a price. Ring 01702 898232 or request a quote, and we will look at how the roof performs in the sun as well as how it holds a person.