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GLASS – LAMINATED VS TOUGHENED

Once upon a time, glass was just glass. As long as you could see through it, surely that was all that mattered. Nowadays, there is a bewildering array of different glass types available for every conceivable purpose: frosted or patterned for protecting your modesty in bathrooms; coloured to funk things up a bit; so-called “self-cleaning” glass to keep the light coming into those hard-to-access areas (in our opinion, it’s a waste of money – it doesn’t work very well at all); solar glass to prevent a room from over-heating in the glare of the sun; and probably most commonly, different forms of safety features, including laminated glass and toughened glass. 

So what’s the difference between laminated glass and toughened glass? Well, first of all they are manufactured differently. Toughened glass is quite often made by heating annealed glass to a very high temperature (over 600⁰C) and then rapidly cooled. This process makes the glass extremely strong due to the way that stress on the glass is balanced throughout it. However, once glass has been through the toughening process, it can’t be reworked – it can’t be cut to size, or have holes drilled through it as this will cause the glass to shatter into tiny pieces. However, it is very strong – often several times stronger than non-toughened glass, which means it can hold a lot of weight. 

Laminated glass consists of two or more layers of glass, held together by an interlayer of another substance (usually polyvinyl butyral (PVB) or ethylene-vinyl acetate (EVA)). This means that when the glass breaks it holds together in one piece. You probably will have seen this in action in cars that have been involved in accidents – their windscreens may have lines criss-crossing all over them, but they are still holding in place. This is important because at the moment of impact, the glass still kept the driver safe – it didn’t shatter all over them, potentially causing untold injuries. 

So, which type of glass is best for roof lights? Well, the short answer is both, but only in combination. To understand why, it’s probably best to start by talking about what a roof light is and what it does. So, a roof light is essentially a window in a roof. Here at Red, our roof lights are suitable for installation in flat roofs or roofs with a pitch of up to 30⁰. So far so good, but because of the fact that they are essentially installed horizontally rather than vertically, unlike standard windows, other things need to be taken into consideration. For example, a standard window needs to be weather-tight – if it rains, you really don’t want to get wet – but because standard windows are usually installed into a vertical wall, rain, hail, sleet and snow all run off quite easily. Not so with a roof light. Most ‘flat roofs’ aren’t actually flat at all – they usually have at least a small pitch (5⁰ is the minimum we recommend), even if it isn’t easily visible to the naked eye. This allows rain to run off and drain away. Snow, on the other hand is a whole different matter. It tends to stick to surfaces and build up, which creates a load that must be taken into account. Snow isn’t often too much of a problem in most parts of the UK, but that’s not true everywhere. It’s also not the only type of load that a rooflight needs to be able to take.
If your roof light is being installed into an accessible area, maybe on a balcony, or even just a roof that you may need to walk on every now and again, you need to make sure it can take the weight of something being dropped on to it, or (and this does happen) someone falling on it. So the glass that you come into contact with has to be strong and reliable. If you’re thinking that this sounds like just the task for toughened glass, you’d be right – well, at least half right. 

The problem is that although toughened glass is really strong, if you catch it at the wrong angle or with something sharp, it is likely to shatter. And that’s no good if you’re several metres above ground – falling through your roof light is not a good idea. But hang on – roof lights are usually double-glazed, so surely the inner pane of glass could also be toughened and that would be enough, right? Wrong. Imagine you’re sitting with your family at the dining table one lunchtime directly below your wonderful roof light that’s letting the sun stream in on you. Now imagine that while you’re eating your lunch, there’s a repairman using your flat roof to access something on the first floor. He’s working away while you’re eating your lunch when he suddenly drops his hammer. It’s not particularly heavy, but it does put sudden pressure onto the outer pane of your roof light, which smashes instantly and the hammer falls onto the inner pane of glass, which is also being hit with a sudden force, so it, too, smashes. You and your family are now being showered in millions of tiny bits of glass, not to mention the hammer that has fallen from several metres above you. Obviously, this scenario is far from ideal. Which is why the inner pane of the roof light needs to be laminated, to prevent the hammer (or you!) from falling through to the floor below. The outer pane provides the strength; the inner pane provides the safety – they work best in combination. 

This might sound obvious now that you’ve read this, but you’d be surprised at the number of roof light companies that don’t supply roof lights with laminated glass. Here at Red, our roof lights aren’t just beautifully designed – they also keep you safe and secure. All of our roof lights include a combination of toughened and laminated glass and we are fully tested and compliant with CWCT 66/67, which regulates the safety and fragility of glazed roofing. For more information on safety standards, please visit our manufacturer’s website here: http://www.vitral.co.uk/en/enviromental-aspects/working-environment 

Remember, not all roof lights are created equal.
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