I own an older two-story home with a second floor porch over a first floor enclosed porch. The upper porch decking is metal, perhaps tin. The metal flooring is rusting in spots and leaking into the lower unit. The upper porch has a door onto it and a full railing, indicating it was intended to be used as a porch. The pitch is from center to front and center to sides. I'm wondering if I can install a product similar to Lockdry watertight aluminum decking over the pitched floor and if so what preparation is required. Do I need to do a tear-off and replace the joists/change the pitch or can it be installed over the existing floor on the same angle? I hope my question is understandable.