Base Cap System Commercial Greenhouse Projects – This greenhouse uses 8mm Lexan Polycarbonate sheet. Application was a recovering of a Home Depot greenhouse. Roofing contractor removed the severely aging polycarb, replaced the yellowed polycarbonate H-Profiles with the Base & Cap Install System and installed new sheets. This is a common occurance, as all roofing has a service life, 20 Year Polycarbonate is a wise choice.