Roofglaze News

May 2011

By Ray Paddick, Technical Manager, Roofglaze Limited

The safety of operatives working on a roof is of paramount importance, during building and routine maintenance.

The ACR (Advisory Committee for Roofsafety) method of testing is applicable to all roofing products and it is an important consideration. However, the test was developed without input from the glass industry.

Glass roofing has traditionally been considered to be fragile. In recent years there has been a move to using non fragile forms of roof construction hence the fragility of glass roofing has had to be considered.

The current ACR test method makes no allowance for the fact that glass is a potentially fragile material. It can withstand heavy impacts without breaking and then sometimes a light blow from a hard object can cause it to shatter.

The ACR method of testing is a soft body impact, designed to replicate a workman falling on to the rooflight. However, if he is carrying a metal tool this could impact the glass first and the glass could be broken before he lands on it.

In order to allow for this eventuality, the CWCT (Centre for Window and Cladding Technology) has developed a test which combines both soft and hard body tests.

In the CWCT glass roofing test, if the glass doesn’t break on impact, it has to be deliberately broken before continuing with the test procedure.

The next stage is a static load test, with both panes of glass broken and only the PVB layer* remaining. A 90kg weight is applied to the rooflight and left in place for 30 minutes. This replicates an injured man laying on the broken glass.

The Work at Height Regulations  emphasise that it is the duty of all employers and of people who have control over workplaces to reduce building risks ‘so far as is reasonably practicable’ under the Health and Safety at Work 1974 and ‘where necessary for reasons of health or safety’ under the Workplace (Health, Safety and Welfare) Regulations 1992.

For this reason and having identified the shortcomings of the ACR method of testing for glass rooflights, the technical team at Roofglaze decided to carry out testing to the CWCT standard. The company had also become aware of increasing acceptance of the CWCT recommendations amongst architects and specifiers: a further driver in the decision to invest in a controlled test.

A test rig was hired on Roofglaze’s behalf, at the premises of partner company Twinfix Limited, manufacturers of panel glazing systems. Tests were carried out over two days, in accordance with the CWCT recommendations. The Roofglaze assembly achieved the required standard for Class 2 certification.

CWCT’s Technical Note outlining the testing procedure specifically addresses non-fragility relating to roofs of shallow slope. Roofs of steeper slope may require a different testing regime as the static load may not be appropriate and impacts may occur in a horizontal direction. It should also be noted that this standard is not applicable to roofs that are accessible by the public which should be designed in a similar manner to glass floors and other walk-on glass surfaces, to meet class 0 for non-fragility. The CWCT Class 2 standard is only applicable to roof areas which may be accessed for cleaning or maintenance.

The CWCT is a leading information provider and trainer in the field of building envelopes and glazing. It is an industry funded Centre based at the University of Bath. The CWCT sets industry Standards and publishes both standards and guidance – and through its members, is able to provide a wide range of advice to the whole construction industry on a consultancy basis.
Based in St Neots, Cambridgeshire, Roofglaze Limited operates on a nationwide basis, providing natural daylight solutions from modular thermoplastic domes to  bespoke structural glass skylights, for many of the UK’s leading contractors as well as architects, developers and end user organisations. Roofglaze is an associate member of NARM, the National Association of Rooflight Manufacturers, and is committed to furthering best practice in all aspects of rooflighting.