Published on 12 August 2019 13:05

Testing and Certification for Glass Rooflights

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Key Learning outcomes
  • Understand the factors which impact loadings
  • Recognise permeability and breathability characteristics
  • Gain knowledge of glass rooflight fire regulations
  • Understand glazing performance requirements for glass rooflights
  • Understand compliant security ratings for glass rooflights
Rooflights are a valuable source of natural light, with glass serving as a durable and hard-wearing material for the purpose. However, it is essential that rooflights are subject to stringent testing and compliant certification, to ensure that structures benefit from a safe roof surface.

Even more inaccessible roves require access and load bearing capabilities from time to time for routine maintenance and emergency repairs. As a result, rooflights need to maintain their ability to withstand load forces, and be manufactured, selected and fitted in such a way that they are not subject to degradation from the elements and accidental damage.

1.0 Understanding how loadings are affected by the environment

Recognising the various loading capacities of glass rooflights is a key aspect of upholding safety. As a result, there are standards established to ensure that the product which is being installed is compliant and suitable for its proposed deployment.

The standard BS EN 12211:2016 (Windows and doors - resistance to wind load) assesses relative frontal deflection and damage resistance to wind loads. It supersedes the previous BS EN 12211:2000 standard, and is applicable to glass rooflights, and specifies the test method to determine the resistance to wind load for completely assembled windows, and pedestrian door sets of any materials, when submitted to positive or negative test pressures.

Load force can be impacted by several criteria. These include external factors such as wind pressure, snowfall, heavy rain or hail, all of which can affect the stability of the glass rooflight. Loading is also affected by geographical site locations, determined by the purpose of the rooflight – for example, a rooflight on a pitched will have significantly different loading requirements in comparison to a glass rooflight placed on a terrace which will be walked upon.

Imposed loads for walk on glass rooflights are defined by Uniform Distributed Load (UDL) and Concentrated Load. Typical standards are:

• Domestic applications: Uniformly distributed load (UDL) from 1.5kN/m2, and Concentrated load from 2.0kN
• Commercial applications: Uniformly distributed load (UDL) 4.0kN/m2, and Concentrated load 3.6kN
• Heavy duty commercial applications: Uniformly distributed load (UDL) 5.0kN/m2, and
Concentrated load 4.5kN.

Loading capacity is also considered in relation with the weight of the rooflight itself, and the overall structure and suitability of the roof and upstand. As a general rule, this is calculated as 2.5kg per m2 per mm of glass plus the weight of the aluminium framework. Similarly, outthrust and span force are also important to consider when selecting the correct rooflight product. For example, when designing and constructing an upstand, it is critical to consider any outthrust forces which the rooflight may impose.

By definition, a pitched rooflight will always try to flatten out. Depending on the span of the rooflight, these forces can be considerable. If building in timber, care must be taken to ensure that the joints are lapped and not abutted, and corner bracing may be required. In some instances, a steel-formed upstand may provide the best solution.
Snow and ice provide additional loadings on rooflights and as different geographical ares have different loading values, careful consideration on design is required.
Snow and ice provide additional loadings on rooflights and as different geographical ares have different loading values, careful consideration on design is required.
 
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Rob Hamblen
Tel +44 (0)1483 917580
rob.hamblen@whitesales.co.uk
The information contained in the CPD article web pages is not intended and accordingly shall not be relied upon either as a substitute for professional advice or judgement or to provide legal or other advice with respect to any particular circumstance. RIBA Enterprises accepts no responsibility for loss occasioned to any person acting or refraining from action as a result of the information contained.
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