Fragile Roof

A fragile roof is a roof or roof element that would not safely support the weight of a person, or of a person plus materials, if they stepped or fell onto it. Falls through fragile surfaces are among the most serious hazards in roof work. In Great Britain, the Health and Safety Executive (HSE) reports that they account for 22% of fatal falls from height in construction, and the National Association of Rooflight Manufacturers has cited a figure of about seven deaths a year (2014). People doing small, short maintenance and cleaning jobs are over-represented.

What can be fragile

HSE lists typical fragile materials as:

• non-reinforced fibre-cement sheets, whatever the profile, including older asbestos-cement sheets, which weathering makes more brittle;
• rooflights, especially those in the roof plane, which can be hard to see in some light or when painted over;
• liner panels on built-up sheeted roofs;
• metal sheets that have corroded;
• glass, including wired glass;
• chipboard and similar boards that have rotted;
• wood wool slabs, slates and tiles.

HSE advises that every roof should be treated as fragile until a competent person confirms otherwise. Industry guidance adds that inspection cannot reliably prove that an existing roof is non-fragile, so existing roofs should be treated as possibly fragile unless documented evidence shows otherwise.

Testing and classification (UK)

In the mid-1990s the roofing industry and HSE formed the Advisory Committee for Roofsafety (ACR) to define non-fragility. Its test, ACR(M)001, drops a sand bag onto a roof assembly on a test rig to simulate a person stumbling and falling. Results are graded:

• Fragile: fails the test.
• Class C: holds the bag after one drop.
• Class B: holds it after two drops in the same place, though damage is likely.
• Class A: after two drops, no damage that would speed deterioration.

Classification applies to the whole assembly (sheets, fixings, washers and supports), not the sheet alone. A rooflight cannot raise an assembly above the class of the surrounding roof, and poor fixing can lower it. ACR also publishes ACR(CP)002, a code of practice for safe working on fragile roofs.

Controls

HSE's approach is to avoid work on fragile surfaces where possible, for example by working from below with a mobile elevating work platform. Where work must go ahead, risks are controlled with staging, guard rails, fall restraint, fall arrest and safety nets slung close beneath the roof. Warning signs should be fixed on the approach to any fragile surface, and workers trained and supervised. HSE's guide Health and safety in roof work (HSG33) covers fragile surfaces in detail, alongside the Work at Height Regulations 2005.

Other jurisdictions

In the United States, OSHA's construction standard 29 CFR 1926.501(b)(4) requires workers to be protected from falling through holes, explicitly including skylights, more than 1.8 m (6 ft) above a lower level, by personal fall arrest systems, covers or guardrails, and from stepping through such holes by covers.