When choosing rooflights for your project, cost and aesthetics are likely the priority over glass or frame technology. However, the choice of glass type and frame design, can have significant safety implications. Here, Tony Isaac from Brett Martin sheds light on selecting the safest rooflights for your project.
Rooflights are a great way to bring extra light into your home, whether you are building your dream kitchen extension or starting from scratch with a brand-new home.
Flat rooflights have become a particularly popular choice in recent years because they offer a sleek and modern aesthetic with minimal frame visibility that’s easy to install and provide maximum access to natural light. However, with this rising popularity has come an increase in the number products on the market, including products that could pose a risk to those in the vicinity should they break.
Sourcing a glass rooflight can be confusing because it may not immediately be obvious which type of glass is used. Many will offer only toughened glass while others offer the higher specification laminated glass. While both types have been engineered to reduce the risk of injury should they break, each has very different characteristics in that event.
What is toughened glass?
Toughened or tempered glass is designed primarily to resist breaking in the first place. To achieve this, a piece of float glass is passed through a furnace and heated to temperatures in excess of 600°C before being rapidly cooled. This process alters the tensile and compressive qualities of the glass, making it resistant to impact from objects such as footballs, which would shatter standard float glass.
However, toughened glass is not indestructible and can be still broken by a focused impact from a metal object, such as the foot of a ladder. Due to the balance of tensile and compressive forces within the glass, when a toughened glass pane does break, while it won’t shatter into shards, it will still ‘pop’ into pieces which can fall on anyone standing below. What’s more, should the edges of the glass be damaged during installation or transportation, the structural integrity of the whole pane can be compromised. This makes it more susceptible to thermal stresses and can lead to the pane ‘popping’, seemingly at random during or after installation.
Laminated glass
Unlike toughened glass, the primary design goal of laminated glass is not only to resist breakage but – if it does break – to break in a way that is both safe and secure. Laminated panes are made from two panes of float glass with a polymer layer bonded between them. This polymer layer doesn’t affect the quality of the light that passes through but it does ensure that, when broken, the glass stays in place as one pane. This often forms a characteristic spider’s web pattern, which, depending on the size of the impact, ensures the integrity of the pane is maintained as much as possible, reducing the likelihood of the broken rooflight falling on any occupants below.
An example of the difference between laminated and toughened glass can be found in car windows. A laminated glass windscreen cracks and stays in situ, protecting occupants from flying debris; whereas the toughened glass side windows will break inwards.
Specifying for safety
Although there is currently nothing prohibiting the use of toughened glass in the majority of residential applications, it is widely acknowledged industry best practice to always specify glass rooflights with a laminated inner pane – and this is mandatory under BS 5516-2 Patent glazing and sloping glazing for buildings if the rooflight is more than five metres above floor level or larger than three metres squared.
Consequently, The Rooflight Association recommends that the best solution is a product that combines both types of safety glass, such as those offered by Brett Martin: an outer pane of toughened glass and a laminated inner pane, to protect people below from falling glass.
Framed or frameless
Another factor that has a considerable impact on the safety of overhead glazing is the design of the rooflight itself. In most flat glass rooflights, the glazing is retained in an aluminium frame, creating a secure stable unit, which is then connected to the roof with screw fixings. However, there are also rooflights available without an aluminium frame, these are secured to the roof with silicone instead of fixings. While the absence of a frame makes these options cheaper, it also introduces significant opportunities for failure of the rooflight. As a result, The Rooflight Association has received reports of multiple unsafe incidents related to frameless glass rooflights.
Consequently, it is important to specify a framed glass rooflights made by trusted manufacturers, where you can be certain that the glass and frame has been designed and tested to withstand both impacts and the elements.
By thoroughly checking the design and spec of a rooflight before you buy, self-builders can guarantee the purchase of a product will provide maximum protection for their family. Despite its name, toughened glass alone does not guarantee enough strength and resilience by itself to provide the safety you want for your home. Laminated glass and a framed design should therefore be considered as a necessary extra line of defence against accidental breakage.