It depends on the size of the deck project – the bigger the project, the more piles required. As well, whether the deck is attached to an existing structure, or if it is free-standing, also makes a difference. A deck attached to an existing structure requires fewer piles with a smaller diameter because the existing structure supports the lateral load. A free-standing deck requires more piles and with a larger diameter in order to support the lateral load. The number of piles /pile location is provided by the deck designer. The rule of thumb is a pile spacing of 8-10 feet between piles.