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Why use Polycarbonate instead of glass?
Glass offers visual clarity, but has drawbacks. Safety glass is required if installed within 12" of a door, 18" of the floor or overhead. In vertical applications tempered glass is okay, but in overhead applications tempered over laminated annealed (windshield type glass) is required. In roof applications this glass cracks easily and is very expensive. For insulation two lites of glass, in an insulated unit, are necessary. The seals eventually fail and the unit will fog. Seal warranty is 5 to 10 years, but is void in high moisture greenhouse and pool enclosure applications.
Since clear glass does not diffuse light hot spots occur in greenhouses. Glass is heavy, requiring a strong frame. A sophisticated install system with aluminum and rubber gaskets is required or leaks occur, especially on overhead glazing. Often numerous lites of glass are required in a roof slope, resulting in horizontal mullion bars that dam water and can easily lead to leaks. Insulated glass should not overhang the eave, requiring a horizontal mullion bar at this location and possible leaks.
Polycarbonate is virtually indestructible and is inherently safety glazing! Football helmets and the inner layers of bullet resistant glass are made of polycarbonate. Multi-wall polycarbonate is inexpensive and has an insulation value similar to insulated glass. Polycarbonate diffuses the light and is very easy to install. One sheet of polycarbonate goes from roof peak to overhanging eave, effectively shedding water.
Polycarbonate is resilient. When Cap is snugly installed, pressure of the Cap cause polycarbonate to slightly give, creating a watertight seal. One of the great advantages to polycarbonate is that gaskets are not required to achieve a watertight seal. The more parts of a glazing system, the more likelihood for leakage. Gaskets in install system caps will often shrink, creating a gap for water to enter.