Using this product for a balcony that has a patio below is there any other product needed with it so there is no leaks?

Hello, and thank you for your interest in Trex! Since Trex decking requires gapping width to width and end to end, Trex decking itself will not be water resistant to the area below, however with the addition of Trex Rain Escapes this can be achieved. Trex Rain Escapes uses a network of troughs and gutters to divert water from the deck while shielding the area below the deck from rain, snow, sun and other elements. For questions about Trex Rain Escapes feel free to contact our customer care team at 877-348-1385. I hope this helps answer your question! Thanks, Tori - Trex Customer Care Team