ZipUP UnderDeck® Pitch Rails are the hidden foundation for the entire ZipUP system, as they form the pitch which directs water away from your home. The system works by creating a slope of 1/8 per foot. Simply put, a 1/2 Pitch Rail needs to be installed 3 feet from the house, then a 1 Pitch Rail 6 feet from the house, and so on, adding 1/2 to the height of the Pitch Rail every 3 feet.