How much of an industrial roof should be skylight?

Commonly 3 to 5 percent of roof area, and ECBC 2017 sets limits alongside daylighting provisions. More than that and solar heat gain starts to outweigh the lighting benefit, especially in Indian conditions where the roof takes intense sun for most of the day. The right figure depends on internal working plane requirements and whether the space is air conditioned.

Which face must point upward?

The UV-protected face, which is marked on the protective film. Polycarbonate degrades rapidly under direct ultraviolet, so the co-extruded UV layer is what gives the sheet its service life. Installing a sheet upside down is an easy site error, it is invisible on the day, and it yellows and embrittles within a couple of seasons.

Is polycarbonate or FRP better for roof lights?

Polycarbonate has far higher impact resistance and better long-term clarity, so it is the safer choice where anything might fall on the roof or where people access it. FRP is cheaper and more rigid but yellows and can become brittle with age. For a building with a long design life, polycarbonate with a proper UV layer is usually the better investment.

Polycarbonate Skylight Sheet

What it is

Translucent polycarbonate sheet, profiled to match the metal roof sheet around it, used to bring daylight into a large industrial or warehouse space without electric lighting.

Specification at a glance

Property	Typical specification
Type	Solid profiled, or multiwall
Thickness	1.5mm — 3mm profiled; 6mm — 25mm multiwall
UV protection	Co-extruded layer, one or both faces
Light transmission	Specified as a percentage
Profile	Matched to the adjacent metal sheet
Fire class	Named EN 13501-1 class

Solid profiled against multiwall

	Solid profiled	Multiwall
Insulation	Poor	Better, sealed air cells
Light quality	Clear, higher transmission	Diffused, softer
Strength	Good impact resistance	Good, lighter
Detailing	Laps like the metal sheet	Needs sealed edge tapes
Use	Standard industrial roof lights	Conditioned or diffused-light spaces

The daylight and heat trade-off

Roof lights cut lighting load — and that saving works against the ECBC lighting power density target — but they also admit solar heat directly onto the working floor. In an air-conditioned building that heat becomes cooling load.

The practical answer on most Indian industrial roofs is a modest percentage of roof area, distributed evenly for uniform light rather than concentrated, with diffusing multiwall used where glare on a working plane matters.

Where projects go wrong

UV face installed downward. The single most common and most damaging error.
Too much skylight area, turning a lighting saving into a cooling cost.
Fixings through the sheet without oversized holes. Polycarbonate expands considerably more than steel; pinned sheets crack around the screws.
Edges of multiwall left unsealed, so dust and moisture enter the cells and the sheet clouds permanently.
Walking on roof lights. They are not a walking surface; many industrial roof falls happen through them.

Standards referenced

Skylight and daylighting provisions under ECBC 2017. Wind loading under IS 875 (Part 3). Reaction-to-fire classification to EN 13501-1.

Polycarbonate Skylight Sheet for Industrial Roofs

What it is

Specification at a glance

Solid profiled against multiwall

The daylight and heat trade-off

Where projects go wrong

Standards referenced

Standards referenced

Frequently asked

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