The domes, or roof covering, of solar tube systems are mostly made from one of three different materials; acrylic, polycarbonate or glass. Whilst each of these materials has its advantages over the others in various applications, glass for example will always be the best option for windows, when it comes to tubular daylight systems acrylic is the clear winner.
The role of the dome, or panel, is simple. It needs to keep the weather out and let the light in, and keep doing this to the highest standard.
Whilst it may seem that all three options may seem to have their merits, two options have such severe draw backs that it makes them both unsuitable for the application when you consider the purpose of the product.
Polycarbonate starts with a massive disadvantage and that is because it is a poor transmitter of light, reducing the amount entering the top by around 10%. The situation is exacerbated further as Polycarbonate is so unstablewhen subjected to UV (daylight) that is goes cloudy and yellow in a matter of a few years – further reducing the input by another 10% (source: BRE – Solatube polycarbonate dome deteriorated a further 10% in just 4 years).
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Glass may seem like a good option, it has a good light transmittance and won’t go yellow, in order to be strong enough to withstand the rigours of conditions on the roof. To give a glass dome the strength it needs it is moulded to a thickness roughly four times that of acrylic or polycarbonate. The result of this additional thickness of glass is a corresponding increase in the amount of light absorbed by the dome. In fact, roughly 50% of the available light that could be entering the tube is blocked out.
Acrylic on the other hand ticks all of the boxes. It has the best light transference of any material, it doesn’t deteriorate when exposed to UV and it’s very strong. And unless you have a really unusual set of building condition to conform to, there are no building regulation restrictions to worry about.
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