Basic deck parts include the ledger and band around the perimeter, floor joists across the middle, and surface boards for flooring. Frame spacing for trex decking refers to the measurement of space that is required between floor joists.
Trex and other composite decking brands are considerably heavier and more flexible than wooden surface boards. Whether you are building a new composite deck or replacing old wooden surface boards on an existing deck, you will need to compensate for the additional weight and flexibility when designing your plans for the frame.
When designing a new trex or composite deck, the spacing between floor joists should be 12 inches on center. On center means that the measurement should be taken from the center of a joist edge to the center of the next joist edge. Joists are typically "two-by" pieces of lumber, most often two inches by eight inches, and the actual measurement of the two inch side is one and one-half inches. This means that the empty space between joists will be 10 and one-half inches.
Wooden decks will have a frame spacing measurement of either 24 or 16 inches. When replacing the existing boards with composite decking on a deck with 24-inch frame spacing, you will only need to add joists 12 inches on center between existing joists. For decks with 16-inch spacing, measure and mark each joist that is at 48 inches. Remove all unmarked joists and rehang at 12 inches on center.