The seal between the Narrow Profile Cap and polycarbonate panel doesn’t look weather tight. 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 5º 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 the Base gasket?
Base gaskets do not assist in achieving watertight integrity and being that polycarbonate is indestructible a cushion is not required. These gaskets will reduce expansion noise. We achieve this with, low cost, high quality, polycarbonate compatible polyurethane foam tape.
Base & Cap Features & Benefits: Cap Screw length accommodates thickness – 8, 10, 16 or 25mm. Available in Clear Satin Anodized and Mill Finish (bare aluminum). The system is strong , spans over purlins and can handle typical loads. Clean looking and narrow 2″ wide Base & Cap profile and thin line U-Profiles to terminate sheet – Low Cost, Strong, Watertight, Attractive and Versatile.
U-Profile Watertight Seal: The critical location, with the greatest potential for leaks is the lower end of roof sheets, at the eave, also described as lower edge of the slope. One must have the long leg of the U-Profile facing the sky and pin the U-Profile to the sheet every 8″ on-center, as shown in the Eave Details, using the 3/8″ self drilling screws provided free. This causes the polycarbonate to dimple slightly. Water hits the 1/64″ leading edge of the U-Profile and cascades off the sheet. Should a slight amount of water make it past a joint of the U-Profiles it will drain out via 1/16″ weep holes, drilled every 12″. See Eave Detail Drawings. Also, no vent tape required, the U-Profile fits snug, but not too tight.