Glass vs Polycarbonate
Optical Clarity
Glass is optically superior to any roof glazing plastic, light transmission is typically 10-15% higher on glass, the difference increasing with age. UV stabilised plastics with a 10 year guarantee should always be specified. Optical distortion will be severe on plastic moulded rooflights. Clarity of roofing plastics will deteriorate with age and accelerate with microscopic abrasion from conventional cleaning processes.
Cost
Based on basic functionality polycarbonate glazing systems are less expensive for curved, pre-moulded or hollow extruded flat panel applications but more expensive for extruded solid sheets.
Cleanability
Most of the contamination on rooflights is deposited by the contamination in the air or rain, when the water evaporates the pollution remains. The Steeper the roof pitch the better the self cleaning characteristics of the glazing. Glass is a polished smooth surface which retains less deposit and is more resistant to environmental staining than typical plastics, enhanced by the flushglaze design of the GV rooflight with no obstructions for water entrapment. Coatings can be applied to improve cleaning characteristics of both materials. Plastic roofing materials have a higher retention of air pollutants worsening with age and surface deterioration.
Fragility
Polycarbonate can be a high impact resistant material if correctly specified and very suitable for high risk areas, glass can be upgraded but at a cost in weight and value.
Expansion
This is much higher with plastics, high temperature variations can induce large movements which requires special design considerations, movement noises are common in plastics.
Noise Transmission
This is high with conventional plastic materials, acoustics of falling rain on polycarbonate can be disturbing, often resonating like peas on a drum.
Weight
Plastics are substantially lighter than glass and much easier to handle.
Life Span
Under the natural ageing process glass is a life time material, current polycarbonates show age degradation and life spans are limited.
Fire Rating
Glass can be upgraded to give the required integrity.
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