Falls through roofs and rooflights are among the most serious accidents in building maintenance. A cement sheet that has looked fine for fifty years can shatter under one footstep. A rooflight painted over, or darkened with moss and dirt, can pass for the steel sheet beside it. The person who steps on it usually has no warning at all.
For an owner or manager the practical point is simple: a roof you have not checked should be treated as fragile until someone competent has shown otherwise. That affects the survey, the quote, the access equipment, the order of work and what we ask you to do on site. It also affects ordinary visits by electricians, aerial fitters and window cleaners, who may not think of a unit roof as a hazard.
Below we explain how roofs become fragile, what to expect from the older materials, how access is planned, and what a sensible job on a fragile roof looks like. This is practical guidance in plain words. It is not a replacement for HSE guidance or for a risk assessment on your own building, and we point to HSE where its pages apply.
How a roof becomes fragile
A roof is fragile when it cannot be relied on to support the weight of a person, with the tools and materials they are carrying. That is a different thing from being old, and different again from looking sound. Strength depends on the covering, its fixings, the spacing of the supports beneath and the condition of all three.
Fibre cement sheets are the best-known example, and HSE guidance A14 puts it bluntly: AC roofs are always fragile. They are brittle by nature, and weathering makes them more so. But the list does not stop there. Single skin steel sheets that have rusted along their edges and at their fixings can lose their grip on the purlins. Built-up roofs with a thin outer sheet over insulation will dent and tear under a boot, because the outer layer does not span the gap. Roofs with a sagging deck, rotten timber or a rotted lining underneath may look intact from above and give way in the middle.
Why looking is not enough
Moss, algae and paint are the problem. Algae growth turns white translucent sheets grey, so that a rooflight can be hard to tell from a metal sheet unless you are close and know what to look for. New paint or a recoat applied by a previous contractor can hide the difference altogether. Snow and wet leaves do the same job in winter. Weather conditions also matter, because a wet surface is slippery whether the roof is fragile or not.
Because of all this, we do not judge a roof by eye alone. We start from the position that any roof of unknown build-up is fragile, and we establish what it is made of and how it is supported before anyone walks on it. Our wider commercial roofing work is planned around that rule.
Cement sheets and old rooflights
Two materials account for much of the risk on older industrial buildings in Worthing, Shoreham and Lancing: cement sheeting and translucent rooflights.
The cement sheets are the old corrugated type, grey or weathered white, laid in the mid twentieth century. HSE tells owners to treat a building as containing asbestos when it dates from before 2000, or was refurbished before then, until a survey shows otherwise. So the two problems arrive together: the sheet is brittle, and breaking it releases fibres. HSE treats careful removal of weathered cement as non-licensed work, provided the sheets are handled without being broken up. If they are substantially damaged, the job turns into notifiable non-licensed work, and HSE names dropping an asbestos cement roof as an example. Our guide to the industrial asbestos roof covers that side in full.
Rooflights that have aged
Translucent sheets let daylight into a building, and over the years the plastic or glass fibre becomes brittle in sunlight and cracks at the fixings. They sit in the same profile as the steel sheets around them, so they are easy to miss from above. A rooflight that has been in place for decades should be treated as unable to bear weight, whatever material it is made of and whatever it looks like. Where the rooflights are in poor condition, the survey records it with photographs, and where they need replacing that becomes part of the proposed job. Rooflight-specific advice is in our guide to industrial rooflights.
Neither material is a reason to panic. Both are common, both can be dealt with, and both are far safer when the people on site know about them in advance. A third case worth naming is a roof that has been overclad at some point: new sheets laid over old ones hide the original material, including any cement beneath. Ask the building's records or the previous contractor what is under the visible layer, and let the survey confirm it, before assuming a recent-looking roof is a modern one.
Looking at the roof without standing on it
The first inspection of a fragile or unknown roof should not need anyone to walk on it. Several routes make that possible, and which one we choose depends on the building.
Often the quickest and least costly is a look from the ground and from the inside. From the yard, binoculars or a zoom lens show lap condition, rooflight positions, stains and failed fixings. From inside, a torch beam along the underside of the sheets shows daylight through holes, rust, wet insulation and sagging. A tide mark on a lining marks the path of a leak much as it does in a house loft.
Next come aids that put eyes closer without putting weight on the roof. A drone gives clear pictures of the whole surface, including ridges and valley gutters. MyBuilder (updated 21/08/2026) gives a typical UK range of £200 to £400 for a drone survey and £150 to £250 for a standard roof inspection. A mobile elevated work platform, the hydraulic lift often called a cherry picker, takes a surveyor up beside an eaves or a gable edge. Where the roof edge can be reached by a scissor lift or a tower, a close look at the first few metres is often enough to see what the build-up is.
When the roof must be walked
Sometimes there is no alternative, because a fix cannot be priced without opening a lap or lifting a sheet. In those cases the walking comes with protection: staging or boards that span across several supports, rather than single steps on the sheet, plus edge protection and nets or covers where rooflights lie in the path. The roof is never entered by the odd chance, and nobody goes up unless there is a plan. Our guide to the commercial roof survey explains what the written report contains.
Safe working methods on a fragile roof
The plan for the work follows from what the survey finds. It starts with identifying every fragile area on the roof, and marking them before anyone starts. Rooflights get covers that are strong enough to take a fall, or are fenced off; edges are protected; and access ways are laid out so that nobody has to step off a safe route to reach the job.
Common arrangements include boards or a staging system laid across the supports, so that weight spreads over several purlins at once. Nets or soft landing systems may be rigged beneath the sheets when the structure allows. A harness has a place, but only as a last line of defence, because a person who is falling through a brittle sheet is not stopped by the fixing point on the roof they have just broken. Collective protection, such as edge guards and covers, comes before personal equipment.
Handling cement sheeting
If the sheets are asbestos cement, further rules apply. HSE guidance A14 says that significant dust from broken-up cement turns the job into notifiable non-licensed work. It also says to lower large pieces to the ground and never to drop them or send them down rubble chutes. Offcuts and debris get a double wrap and a label, and the cement sheet goes into a lockable skip, because an ordinary skip with sheeting thrown across it is not good enough. The same guidance also asks whether new sheets can go over the old instead of stripping them, which keeps the fibres undisturbed. That route is covered in our guide to overcladding a metal roof.
Where a job involves material that calls for a specialist, the survey notes name the work involved and who should carry it out, so you are never left to guess.
What owners and managers can do
Responsibility for a roof does not end when a contractor arrives. If you own or manage the building, the most useful things you can do are practical and cost nothing.
Tell us, and everyone else who visits, what you know. Where are the rooflights? Has the roof ever been recoated? Did a previous contractor mention asbestos, and is there a survey report or register? Is there a roof hatch, a fixed ladder or a safe route up, and who holds the key? If a previous visitor went through a sheet or a rooflight, say so. These details change both the plan and the quote.
Keep a record. A simple roof plan marked with fragile areas and a few dated photographs help every future visitor, from the alarm engineer to the next roofer. Put clear warning signs at the access points, and keep casual visitors off the roof. If the building is multi-let, make sure each tenant knows the roof is out of bounds unless a competent person is going up.
What the job costs and how it is agreed
Fragile roofs add time and equipment to a job, and the access method is a real cost driver, alongside the area to be covered and the type of covering found. Quoting blind on a phone call would only be guesswork. Typical items that add cost are a lift or tower for the eaves, edge protection along a long run, staging across the sheets, covers for each rooflight and extra time for careful handling. Once the survey is finished, our written quote gives a single total, photographs mark the fragile areas and the access we propose, and the scope says whether sheets are being replaced or only fixings and laps are being renewed.
If a roof on your premises is cracked, rusting or covered in old sheeting and you are unsure whether it is safe, send us a few photographs from the ground, along with the building age and use. We can tell you what we would check first and how we would reach the roof.
