How does non-fragility affect glass rooflight specification (in the UK)?

Back to all blogs | Glazing Vision Europe | Need to know

When it comes to the design and performance of glass rooflights, it’s usually aesthetics and thermal performance that are top of the list of specification considerations. However, the performance of the rooflight for safety, as an overall part of the roof, is another important factor.

It is important to note that in the UK there is no legal requirement for rooflights to be non-fragile; it is only relevant if the customer has specified that requirement. However, it would generally be considered good practice to make roofs non-fragile where possible. Outside of the UK, every country has its own rules and regulations.

A risk assessment should be undertaken to control the risks around any roof work, both during construction and for subsequent maintenance activities, with relevant measures being put in place dependent on the roof type. All overhead glass does have to be a safety glass, either toughened, laminated or wired glass. Heat strengthened glass is not a safety glass. This will be discussed later, in relation to which glass type is most appropriate for various locations.

Classification of Non-Fragility for Roofs

Glazed roofs can be classified in one of the following four types:

  • Class 0: Unrestricted Access; high standard glass designed to be walked upon.
  • Class 1: Roofs that will be walked upon for occasional cleaning/maintenance; they will support the weight of people and any equipment without the glass breaking.
  • Class 2: Not designed to be walked upon, but are required to be non-fragile in the event of a maintenance person falling onto the surface. They will support their fall but the glass may be damaged.
  • Class 3: Roofs considered to be fragile; additional measures and safety considerations are to be specified such as a supporting handrail.

Once the roof class has been defined the correct specification of rooflight for a particular project can be identified.

What standards apply to rooflight specification?

The main standard that applies to rooflight specification is BS5516-2. This gives recommendations for design, properties and maintenance of sloping glass and plastics glazing sheet materials in overhead situations in the envelope and interiors of buildings. It includes those situations where the sloping glazing extends down to floor level.

The Advisory Committee for Roof Safety red book, ACR[M]001:2014 defines the tests for non-fragility.

For glass rooflights the ACR document references CWCT test guidelines, which have been adopted specifically for glass roof lights. It is important to note that not all roof lights have to be CWCT tested.

Within the CWCT guidelines, of particular note are TN66, TN67 and TN92.

TN66 – This Technical Note provides guidance on safety issues relating to access to glass roofs and maintenance of glass roofs which are not accessible by the public but where people carrying out maintenance to the roof, or to other equipment mounted on the roof, may walk, fall or drop objects onto the glazed part of the roof.

TN67 – This Technical Note describes the testing and assessment of glass roofs to establish compliance with the classification system set out in TN66 and described above.

TN92 – This Technical Note defines ‘deemed to satisfy’ criteria and a simplified test method for glass for use in class 2 roofs.

Considerations for specifying the appropriate rooflight

Ultimately, the type of rooflight and its application will define the requirements. Will the rooflight be used for access, ventilation, light or space?

The choice of glass used for the rooflight will depend upon the roof classification required for a particular project (as defined by the roof class, above).

At this stage, the following factors are important to consider:

– Usage

The intended use of the rooflight is an important aspect to consider. In the case of walk on glass, which is outside the scope of TN66 & 67 and has no single specification to cover all potential uses, the glass must be designed to accommodate floor loads in accordance with EN1991-1-1. The glass make up can differ considerably between standard domestic loads in a private home compared to crowd loads in public buildings such as shops, restaurants and museums. Therefore it is critical that the specifier understands completely the intended use of the glass so that proper precautions can be made when calculating the glazed unit.

– Location

The obvious issue with regards to location is access; can people gain access to the glass? Consideration should be given to where the glass is situated where it could be indirectly affected by other activities carried out on the building. If maintenance tasks are going to be carried out above the glazing such as cleaning windows or maintaining guttering or drainage systems, can tools be dropped on to the glass from above? In addition to this, the location of the glass may also determine the size, shape and weight of each glazed section that can feasibly be specified, so that the glass can be manoeuvred into position and installed to acceptable standards.

How access rooflights can transform a living space

Glazing Vision Europe | Need to know

It’s easy to see why outdoor spaces are so highly desired among potential homebuyers. However, with space often at a premium, architects, designers and house builders are looking for creative ways to provide this luxury living space. This is where access box rooflights can provide an excellent solution. Outdoor...

Read more

What specifiers need to know about installing roof windows and rooflights

Glazing Vision Europe | Need to know

The benefits of specifying roof windows and rooflights are clear: they provide high levels of natural light, they can be wonderful sources of ventilation, and they contribute to the thermal comfort of a building. Roof windows and rooflights also provide an aesthetically pleasing addition to the external appearance of...

Read more

Daylight Award for Tim de Graags ‘House 20×3’ in Zierikzee (NL)

Glazing Vision Europe | Spotlight-Daylight

House 20×3 of young Dutch architect Tim de Graag has been rewarded the 2016 Daylight Award . Two rooflights of Glazing Vision were part of the concept. The jury praised the thoughtful approach on the existing section and appreciated the clever routing, the sightline all the way through the building...

Read more

In the spotlight: Sliding Rooflight in Asse – Belgium

Glazing Vision Europe | Spotlight-Daylight

In the historical centre of Asse, next to the market square you can find this luxurious project with domestic and commercial properties ‘In de wolken’ (‘into the clouds’). The roof top terrace has a wonderful view on the 17th century St Pieterschurch. Glazing Visions 3 Wall Sliding Box provides...

Read more

In the spotlight: rooftop access Amsterdam Loft

Glazing Vision Europe | Spotlight-Daylight

Amazing old school conversion to a beautiful light loft. In the Blankenstraat in Amsterdam the former public primary school transformed into loft appartments and offices. The large windows and high ceiling bring a feeling of space and light. For even more space the owners made the rooftop accessible and...

Read more

Easy installation Flushglaze Rooflight Step by step

Glazing Vision Europe | Tutorials

Read more

Kerb Top Trim for a neat finish

Glazing Vision Europe | Tutorials

A kerb top trim hides the upstand and internal finishes such as plasterboard and insulation when viewed through the glass from above.   How does it work? The Kerb Top Trim is a finishing kit designed to be fixed onto existing up-stands providing a clean finish for rooflights which...

Read more

Anti slip glass for walk on rooflights

Glazing Vision Europe | Need to know

Glass can become slippery when wet and common sense should be applied when specifying this material for walk on applications such as walk on rooflights. This is of particular importance when the glass is being installed where the public can access it. On a private dwelling it is less...

Read more

Walkon glass in a roof terrace

Glazing Vision Europe | Need to know

Walkon glass that allows sunlight to flood the room below is designed for UK domestic floor loads and can be used for any fixed areas to create stretches of glass roof. And if you’re looking for something more unusual, you might be surprised at just what our bespoke design...

Read more