Polycarbonate Roofing Sheet
Polycarbonate Sheet
Daylight through the roof
Polycarbonate roofing sheet is profiled to match standard metal roofing, so it drops straight into the run and laps into the sheets either side without special detailing. This is the ordinary industrial roof light.
The reason to fit them is running cost. On a shed with no roof lights the artificial lighting stays on all day. Replacing a proportion of the metal sheets with translucent ones in the same profile removes most of that load during daylight hours.
How many, and where
More is not better. Every roof light is also a heat gain, so an over-glazed roof is bright and hot. The usual approach is a modest percentage of the roof area, distributed evenly along the run so the light is even, rather than concentrated in one bay.
Placing them in the same position in each bay also keeps the roof visually regular, and makes it obvious to anyone working on the roof later where the non-load-bearing panels are.
UV protection is the specification that matters
Bare polycarbonate yellows and loses light transmission under Indian sun. A sheet with a UV protected surface holds its transmission far longer, and this is the single biggest difference between a sheet that is still doing its job in ten years and one that has gone amber and brittle in three.
The protected face has to go outward. A UV protected sheet installed upside down loses the entire benefit, and it is not obvious once the roof is finished.
Thermal movement and fixing
Polycarbonate expands and contracts considerably more than steel with temperature. Fixed tight through undersized holes, it has nowhere to go, and it cracks at the fixings, which is exactly where water then enters.
Holes must be oversized so the sheet can move, and fasteners set firm but not crushed. This is the most common cause of failure on an otherwise sound roof light, and it is entirely avoidable at installation.
Walking on roof lights
They are not walkways. A polycarbonate panel is far more impact resistant than FRP, which is one of its advantages, but it is not a load-bearing sheet and it should not be treated as one during maintenance.
What to send us for a quote
The profile of the surrounding metal sheet, the sheet length, and how many lights you want in the run. If you are matching an existing roof, a photograph of the profile is usually enough for us to identify it.
Frequently asked questions
How many roof lights should a shed have?
A modest proportion of the roof area, spread evenly. Over-glazing makes the building bright but hot, so more is not better.
Why do polycarbonate sheets go yellow?
Ultraviolet degradation. A sheet with a UV protected surface resists it for far longer, provided the protected face is installed outward.
Can I walk on them?
No. They are more impact resistant than FRP but they are not load bearing. Foot traffic during maintenance should be on the metal sheets over a purlin.
Why do they crack at the screws?
Almost always because the fixing holes were not oversized. Polycarbonate moves considerably with temperature and it must be able to. Pinned tight, it cracks.
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