Aluminum Base & Cap Install System:
The seal between the Cap and polycarbonate panel doesn’t look weathertight. Why does water not enter without a gasket seal?
Properly installed, the Cap, of the Base & Cap System, provides an excellent seal, even on a 1/12 (5%) pitch. Glass and acrylic are hard materials, requiring a gasket type seal on the glazing system cap. Polycarbonate is a resilient material. When the Cap is snugly installed, the pressure of the legs of the Cap causes the polycarbonate to give slightly, creating a watertight seal. Similar to the effect achieved with Tupperware, and it’s liquid holding ability.
One of the great advantages to polycarbonate is that gaskets are not required to achieve a watertight seal. Gasket systems can double the cost. More aluminum is required to provide a channel for the gaskets, then there is the cost of the gasket.
Also, the more parts of a glazing system, the more likelihood for leakage. Gaskets in glazing system caps will often shrink, creating a gap for water to enter. Because one sheet of polycarbonate runs from the ridge of a greenhouse, or skylight, to the overhanging eave, there are no horizontal joints, no impediments to water shedding off the glazing area, no water damming up, and consequently, leakage rarely occurs.
Okay, what about a Base gasket?
Base gaskets do not assist in achieving watertight integrity and being that polycarbonate is indestructible a cushion is not required.