More than 2 million decks are built and replaced each year in North America. InterNACHI estimates that of the 45 million existing decks, only 40% are completely safe. The factors in play when a deck collapses might surprise you. There is no correlation between deck failure and whether the deck was built with or without a building permit. There is also no correlation between deck failure and whether the deck was built by a homeowner or a professional contractor. There is only a slight correlation between deck failure and the age of the deck. About 90% of deck collapses occurred as a result of the separation of the house and the deck ledger board, allowing the deck to swing away from the house. It is very rare for deck floor joists to break mid-span. Most injuries are the result of rail failure, rather than complete deck collapse.