A fragile roof is one that cannot be relied on to carry the weight of a person, and on a commercial building that description covers more of the roof than most people expect. Old cement sheets, corroded steel, sun-aged plastic rooflights and the thin liner panel under a double-skin roof can all give way without warning. Because the surface often looks solid from above, the danger is easy to miss. This guide sets out what makes a roof fragile, who carries the duty to prevent a fall, and how access should be planned before anyone climbs a ladder.
What makes a commercial roof fragile
Fragility is a property of the material and its condition, not of the building type. A factory, a retail unit, a school hall and a farm store can all share the same hazard. The main culprits are worth knowing by name, because each fails in its own way.
Profiled fibre cement sheets, including the asbestos cement sheets fitted to many industrial units and agricultural buildings before the 1990s, are brittle. They can look sound and carry a coat of moss, yet crack under a boot placed between two supports. Age adds to the problem, because the material becomes more brittle over time. Where there is any chance the sheets contain asbestos, the work also falls under separate rules, which we cover in our guide to asbestos cement roofs on commercial buildings.
Corroded metal sheeting is the second group. Steel sheets lose strength where rust eats the cut edges, the laps and the areas around the fixings. A sheet that has been fine for twenty years can fail at a corroded lap the first time someone puts weight on it. Our page on cut edge corrosion explains how that damage starts and spreads.
Then there are the layers inside a built-up roof. In a double-skin system the outer sheet sits over insulation, and under that sits a liner panel that was only ever meant to hold the insulation up. A person who breaks through the outer sheet may land on a liner that carries nothing at all. Wood-wool slabs, old glazed lights and any sheet that has lost fixings complete the list.
Rooflights: the hazard hiding in plain sight
Rooflights deserve their own section because they are the single most likely place for a fall through a roof that is otherwise sound. A profiled steel sheet roof may be perfectly capable of taking foot traffic along the correct route, while the translucent sheet set into it a metre away is not.
Most older rooflights are made from glass-reinforced plastic or PVC sheet. Both degrade in sunlight. The surface chalks, the sheet yellows and the material loses the toughness it had when new. Dirt, moss and paint then disguise it, so that from a few metres away it blends into the roof. Wired glass is no better. The wire holds shards together after impact, but it does not stop the pane from breaking under a person's weight.
Several features make rooflights worse than they appear. They are often the same colour as the sheets around them once grime builds up. They sit in the same profile and line, so a person walking a straight route can step onto one without seeing the join. And in a long run of lights, a crack in one sheet may already have been patched with sealant that is carrying no strength whatever.
New rooflights are manufactured to resist a person falling onto them, and they carry a marking to show it. That does not make them safe to stand on. Even a modern rooflight should be treated as a hole in the roof until the whole system is understood, and anything with an unknown history should be assumed fragile. If a rooflight has reached the end of its life, our page on replacing rooflights on industrial roofs covers the options.
Who is responsible for preventing a fall
The Work at Height Regulations 2005 apply to commercial roof work, and the Health and Safety Executive publishes guidance on roof work, including specific advice on fragile surfaces, on its construction pages. The principle is a simple order of thinking. First, avoid work at height if the job can be done another way. Where it cannot be avoided, prevent falls with proper equipment. Only after that do you reduce the distance and the consequences of a fall that might still happen.
The duty does not sit with a single person. The building owner or occupier who sends someone onto a roof, the facilities manager who books a gutter clear, the contractor who accepts the job and the individual who goes up all have a part. If you hold a lease, the repair covenant may also decide who pays for making the roof safe to reach, which our guide on who repairs the roof, landlord or tenant works through. We are not lawyers, so check your lease and your own duties with your adviser, and use the HSE guidance as the starting point for your risk assessment.
In practice this means every visit to a commercial roof, however minor, needs a plan. A person who is only going up to look at a leak, check a flue or fit an aerial needs the same protection as a roofer with a crew, and often has less knowledge of the hazard.
Planning access before anyone climbs
Good access planning starts on the ground. Before a ladder is footed, someone should establish what the roof is made of, what condition it is in, where the rooflights are and how people will reach the work area. That information often exists already in a previous survey or in the building's maintenance file. If it does not, the first visit should be a survey carried out from a safe position, not an exploratory walk.
There are several safer ways to look at a roof. A cherry picker or a mobile access tower puts the surveyor beside the roof rather than on it. A drone can photograph a large roof without anyone leaving the ground. Internal inspection from below, during a dry spell and again during rain, shows light coming through at laps and rooflights. None of these replaces a close look at the fixings and laps, but they let you plan the safe route in.
Where someone does have to go onto the roof, the route should be decided in advance and kept to. On a roof with fragile sheets, that usually means a purpose-made staging or walkway system laid over the roof, with edge protection at the perimeter. A plan should also say who is on the roof, how they get on and off, and what happens if someone is hurt. Nothing about that is complicated, but it has to be written down before the work starts, not improvised.
Edge protection and openings
Fragile roofs usually have an open edge as well, and the two hazards compound each other. Guard rails at the eaves and gable stop a person walking or falling off the side, while guarding or covers on openings stop a fall through the surface. Our guide to what edge protection a commercial roof needs covers the perimeter in more detail.
Protecting people on and under a fragile roof
Once access is planned, the working method has to protect the people on the roof and those underneath. The usual measures work in layers, and each does a different job.
| Measure | What it does | Where it fits |
|---|---|---|
| Staging or crawling boards | Spreads the load across several supports and gives a defined route | Walkways over sheets and along the ridge |
| Rooflight covers or fixed guards | Stops a person stepping onto or falling through a light | Every rooflight within reach of the work |
| Edge protection | Stops a fall from the eaves, verge or gable | The perimeter of the working area |
| Safety netting beneath the roof | Catches a person who breaks through | Under sheets, from inside the building |
| Harness and fixed anchor | Restrains a worker inside a defined zone | As a back-up where rails are not possible |
Staging and covers are the first line, because they stop the fall happening. Nets are a second line, which limit the harm if it does, and a harness is a last resort that depends on the person using it correctly and on a sound anchor point. A fragile sheet is a poor anchor, so a harness should never be clipped to the roof covering itself.
The people underneath matter just as much. A sheet that breaks sends fragments, dust and sometimes the person through to the floor of a warehouse or workshop. Where a roof is being worked on, the area below should be cleared, or covered, and anyone who needs to pass under it told what is happening. For working shops and warehouses that cannot shut, our page on roof work while a business is trading explains how the work can be sequenced around the people below.
Keeping other trades and visitors off the roof
The riskiest visitors to a fragile roof are often not roofers. Solar installers, aerial fitters, air-conditioning engineers, window cleaners and people clearing gutters all arrive with a job to do and no knowledge of the roof beneath them. A handful of simple controls reduces that risk.
- Fix a clear warning sign at every roof access point, stating that the roof is fragile.
- Keep the access hatch, ladder or door secured, so that nobody goes up unannounced.
- Mark rooflights in a way that cannot weather away, such as a fixed guard, rather than a painted cross.
- Keep a roof access permit in place, so that anyone going up has been told the route and the hazards.
- Brief every contractor before they go up, and record that you did.
It is worth keeping a short record of the roof as well: what it is made of, where the rooflights are, when it was last inspected and what protection is in place. A planned programme of checks, such as the one in our guide to planned maintenance for commercial roofs, gives that record somewhere to live.
What we do when we survey a fragile roof
Our free survey of a commercial roof starts from the same principle as everything above: we do not step onto anything we cannot prove will carry us. We look at the roof from safe positions first, and where the roof has to be crossed, we plan the route and protect it before we use it.
We photograph what we find, including each rooflight, any corroded laps, loose fixings and areas where the covering looks tired, so that you see your own roof rather than a generic diagram. The written report sets out what we found, what needs protecting, whether repair or replacement is the right call, and a fixed quote. If a repair will do, we say so. If the roof is fragile throughout and a safe repair is not realistic, we explain what the alternatives are, such as overcladding, which our guide on overcladding a commercial roof describes.
Whatever we fit is backed by a written 10-year workmanship guarantee, and the site is left clear of debris. The wider range of business-premises work is on our commercial roofing in Basingstoke page. A fragile-roof survey can be requested on 01256 213956, or by WhatsApp to the same number.
