Many home owners are under the false impression that products such as composite decking boards can extend the life of their deck indefinitely. One reason this is inaccurate is that, while the deck boards may not deteriorate due to weathering, unless they choose an alternative material, the wooden frame beneath will.
By using pressure treated lumber, most decks will last for two decades, or more, with proper treatment, but over time the lumber will still suffer rot. One way to slow this process is through the installation of joist cap.