Falls through roofs are among the most serious accidents in building maintenance, and many happen on roofs that looked solid. A fragile roof is one that cannot be relied on to support the weight of a person, and it may fail without any warning. Old rooflights are the classic example, but whole roofs can be fragile too, from cement sheets that have become brittle to steel sheets rusted thin. If you own, manage or lease a commercial building, the question is not only whether the roof leaks. It is who goes up on it, what they stand on and what stops them falling. This guide explains the common fragile materials, the signs that show a roof is one, the practical measures owners use, and how to approach the legal side without guessing. What follows is general information rather than legal advice, and the Health and Safety Executive remains the authority on what the law requires.
What makes a roof fragile
Fragility has nothing to do with how a roof looks from the ground. It depends on the material, its age and its condition. Some materials are fragile from new, others become fragile as they age, and some simply cannot be judged by eye.
The usual suspects on commercial and industrial buildings are these:
- Rooflights. Plastic and glass-reinforced rooflights are designed to let in light, not to bear weight. Sunlight and weather make plastic brittle and chalky, and older ones can crack under a person's footfall.
- Asbestos cement sheets. Brittle, easily cracked and capable of giving way without notice. They also bring the asbestos question, which we deal with on the industrial asbestos page.
- Corroded metal sheets. Sheets that have rusted thin, usually along the laps and around fixings, may not support a person. Our guide to cut-edge corrosion explains how that happens.
- Liner panels and old fibre sheets. The inner skin of a built-up metal roof is thin, and the outer sheet above it may hide a gap.
- Painted-over or moss-covered surfaces. A rooflight under a coat of paint or a layer of moss looks like the roof around it, and the camouflage is the danger.
The rule is simple and strict. Treat any roof of an unknown or doubtful material as fragile until a competent person has confirmed that it is not.
How to recognise a fragile roof from the ground
You cannot judge a roof's strength by looking, but you can collect clues that tell you to be careful. The commonest are age, a roof with a patchwork of repairs, patches of different colour or texture, and any translucent panel in the slope. In a roof of profiled sheets, translucent strips running up the slope usually mark rooflights. A long row of small patches on a tiled or sheeted roof can mark places where old rooflights have been covered over.
Look at the building records, too. Drawings, previous survey reports and the health and safety file may name the roof materials and note which areas are fragile. If they do not, assume the worst and have the roof surveyed from a safe position or by a method that does not need anyone to stand on it. Pole cameras and drone surveys can show the surface condition without a person ever stepping onto the roof, which is one reason to consider them as a first step. Our guide to a commercial roof inspection covers what each method can and cannot tell you.
Walkways deserve a mention here. A marked, load-bearing route across the roof to the plant or the hatch keeps visitors away from the weak areas, but only if it is laid over sound structure and kept clear. A walkway that ends at a rooflight is worse than none.
Remember that fragility can change. A rooflight that took a person's weight ten years ago may not do so now, and a coating applied for waterproofing can hide the warning signs. Always treat historical statements about strength as out of date.
Controls owners and managers put in place
The practical aim is to keep people off fragile surfaces, and where they must work near them, to stop a fall from becoming a fatality. In rough order of preference, the measures are:
- Avoid going up. Many inspections can be done from a mobile platform, a drone or a pole camera.
- Fit permanent protection. Guardrails round the roof edge, covers or guards over rooflights and a fixed route to walk on all reduce the risk for everyone who follows.
- Use temporary protection. Edge protection, crawling boards, and nets or safety mesh fitted under fragile sheets, installed by people trained to do it.
- Restrict access. A locked roof hatch, a signed and controlled ladder, and a permit system so nobody goes up unannounced.
- Mark the hazard. Warning signs at the access point and on the roof, with fragile areas clearly shown.
A fall arrest system, which is a fixed anchor or line that a worker clips on to, can be part of the answer on some roofs, and we explain how those fit in our page on roof fall arrest systems. The system only protects the person wearing the harness, so it does not make a fragile surface safe for others, and the anchor points must be suitable for the roof structure.
Weather adds to the hazard. Wet moss, frost and morning dew make sheets slippery, and wind catches boards and sheets being carried across an open roof. Poor light in winter hides the pale shapes of rooflights. Work on a fragile roof is therefore planned for the conditions, and it stops when they turn against it.
Maintenance people are a risk group in their own right. The window cleaner, the aerial contractor or the engineer servicing a rooftop unit may have no reason to know which areas are fragile. Rules about who may access the roof, and how, should reach all of them.
Your duties as the owner, landlord or tenant
The Work at Height Regulations 2005 apply to roof work, and the duties fall on employers and on the people who control the work and the premises. That can mean the owner, the managing agent, the tenant or the employer, depending on who has control of which part of the building. The law does not stop at the wall of a leased unit, and a lease that makes the tenant responsible for repairs does not remove every duty from the landlord.
Regulation 9 deals with fragile surfaces directly. Nobody should work on or near one where the job can reasonably be done safely without it. Where that is not possible, platforms, coverings, guard rails or similar protection must be provided, and prominent warning notices fixed at the approach where reasonably practicable. In general terms, anyone who arranges for work on a roof is expected to plan it, to use people who are competent for it, and to make sure that the work is done in a way that prevents falls. The Health and Safety Executive publishes guidance on roof work, including fragile surfaces, at its site: HSE guidance on roof work. It is the right place to check what applies to your building, and for particular questions your own adviser or the HSE should be your source rather than a roofing contractor.
Records matter as much as the physical measures. A roof can be well guarded and still leave an owner exposed if nobody wrote down what was done, when it was last checked, and who was told. Keep survey reports, permits, and the roof plan together, and review them after any repair, because each repair can change which areas are fragile.
The practical test is what you could show if asked. Do you know which areas of the roof are fragile? Is that written down? Do contractors receive that information before they go up? Is access controlled, and does the control work in practice? A building where those answers are clear is far better placed than one where nobody has looked.
If you rent your unit, read the lease as well. Our page on commercial lease roof repairs explains how responsibility for repairs is often divided, and why it matters for who must act on a dangerous roof.
Replacing and guarding rooflights
When a rooflight is old, there are three realistic options. It can be left in place and protected, it can be replaced with a rooflight that is rated for its use, or it can be removed and the opening sheeted over. Each has consequences for daylight, ventilation, energy use and cost.
Leaving an old rooflight with a protective cover or a guard may be the cheapest step and can be fitted quickly. It does not improve the rooflight, which will keep ageing, and it needs to be inspected so the cover remains secure. Replacement gives a new unit with a known rating, and it is the usual choice when the surrounding sheets or the insulation are being replaced as well. Removing a rooflight saves on glazing but takes light away from the floor, and in a working building that can mean extra electric lighting.
Whichever route you choose, a new rooflight should be marked with its load rating, and the information passed on to anyone who will later work on the roof. Our guide to replacing industrial rooflights covers the options in more detail.
Rooflights also leak, usually where the sealant or the upstand around them has failed. A leak is often the first prompt to look at the rooflight, and the moment to ask about its strength as well.
Safety when roof work is under way
Once a contractor is on site, the safety arrangements are shared between the contractor and the building owner. The owner supplies what they know about the building: which areas are fragile, where the access points and services are, and what hazards exist. The contractor produces a plan for the work, sets out the protection to be used, and manages the roof while it is theirs.
If your business carries on trading during the roof work, there are extra points to agree. Where do people walk beneath the work, and are the areas under the roof closed off? Is stock or machinery directly under a fragile area? Who is told when the roof is occupied? We cover these in the page on roof work with the business open.
New membranes bring their own considerations. A single-ply roof can be slippery when wet, and walkways are often laid for maintenance access over it. Our page on single-ply roofing explains how those systems are laid, and you can read about our wider commercial work on the commercial roofing page.
When we survey a roof, we assume the surface is fragile until proven otherwise, work from protected positions, and photograph what we find. If you know the roof has old cement sheets or plastic rooflights, mention it when you call, because that changes the access we bring and the time the survey needs.