Whether decking boards shrinks or swells depends on the material used to build the deck. Wood that isn’t pressure treated will definitely expand and contract when wet. When it dries, the wood will shrink. These cycles will eventually cause wood decking to warp and crack. This is even true of cedar decking and redwood decking as it ages.
Composite decking doesn’t absorb moisture, but it does expand and contract in the length with the temperature variation.
It’s important to read our installation guide before installing Green Plank composite decking material. When it gets warm, it expands more than wood along its length but less across its width. The longer the decking board, the greater its expansion and the more you have to account for this when building your deck. Check the product’s end-gap chart (head-to-head), which describes the space needed between the ends of two decking boards with the length of each board, the temperature during installation, and the highest ambient temperature you expect in the deck area. For example, a 5 meters long composite deck board installed at 10 degrees Celsius could expand by as much as 3 mm on each end of the board, so you’ll need minimum 6 mm gap between the ends of two decking boards.