When specifying a glass building element, safety is a major consideration. This is certainly true for access rooflights, since users will have direct contact with the glazing.
For example, users will be opening and closing the doors of access rooflights. This means that they might lean on or impact the glass walls of box rooflights and some units might be directly walked over.
Approved Document K provides guidance for protecting against injuries related to impacts against glazing.
Precautions in case of breakage or impact
Part K4 states that glazing, with which people are likely to come into contact whilst moving in or about the building shall:
a) if broken on impact, break in a way which is unlikely to cause injury; or
b) resist impact without breaking; or
c) be shielded or protected from impact.
In practice, this means that in critical locations, at least one of the following approaches should be adopted:
a) The glazing used should be reasonably safe – meaning that if breakage did occur, any particles would be relatively harmless.
b) The glazing used should be sufficiently robust, ensuring that there is a low risk of breakage.
c) Steps should be taken to limit the risk of contact with the glazing.
The use of toughened safety glass is one of the most common solutions for meeting the requirements in rooflights. This type of glass is designed to fracture into smaller, less harmful pieces if a breakages occurs.
Heat soak tested toughened safety glass is another option and glass can also be provided with a laminated layer, which helps to hold fractured sections of glass together, preventing them from falling out of the frame. The right type of safety glass will depend on the situation.
Manifestation of glazing
Since glass used in rooflights is typically transparent, there’s a risk that people will not see it and run into it. Therefore, precautions should be taken to ensure the visual manifestation of the glazing.
Part K5.2 requires that transparent glazing, with which people are likely to come into contact while moving in or about the building, incorporates features that make it apparent. This requirement does not apply to dwellings.
In most cases, the manifestation needs to be included at two levels. It should contrast visually with the background seen through the glass, both from inside and outside in all lighting conditions.
Depending on the situation, alternative indications of glazing – such as mullions, transoms, door framing or large pull or push handles may also be appropriate.
Beyond Part K
While Part K provides thorough guidance in terms of safety against impact and collision, other standards must also be considered when specifying the glazing for rooflights.
For instance, BS5516-2 provides recommendations for design, properties and maintenance of sloping glass and plastic glazing sheet materials in overhead situations.
The Centre for Window and Cladding Technology (CWCT) offers TN66, a technical note that provides guidance on safety issues and non-fragility in glass roofs used for maintenance purposes. TN67 describes the testing and non-fragility testing, which is intended to reduce the chance of potential hazards arising from either people or objects impacting with the glass.
Meanwhile, walk-on glass that’s outside the scope of TN66 and TN67 should be able to accommodate floor loads in accordance with EN1991-1-1 (2002) Actions on Structures.
To find out more about Part K and how to comply with its recommendations when specifying rooflights, download our whitepaper: Approved Document K and Access Rooflights: A specifier’s guide to designing for roof access in dwellings.