One of the most important things to remember when installing any type of material is to follow the manufacturer’s instructions. This is true no matter whether you are dealing with ceramic tile, drywall, paint or composite deck boards. While it might seem like a good idea to butt the joints of the deck boards tight to each other, the reality is that the material needs space to breathe just as much as natural wood does.
All materials have seasonal movement. During the summer months when the temperatures are warm, things tend to swell as they expand in the presence of heat. In the winter months they contract once again as they react to the cold. Composite decking suffers from seasonal movement as much as any other material, growing and shrinking with seasonal temperatures.
Movement is translated throughout a deck, from the joists to the actual deck boards. While some movement is from settling over time, foot traffic is another culprit that can cause vibrations and other types of movements in the deck boards. As the movement carries throughout the deck, it looks for areas where that energy can dissipate. If it cannot, it will cause damage to the material when it comes against an area where it cannot transfer further.
If you butt joint your composite deck boards, the first thing that will happen is buckling. This is where the pressure from expansion and foot traffic isn’t allowed to dissipate or otherwise transfer out and away from the boards. Instead, this pressure transfers directly against the adjacent boards, causing them to pop up off the joists or otherwise buckle upward from the pressure.
Slight spacing is required in any type of deck construction, regardless of the material. When installing your composite deck boards, put a spacer--such as a carpenter's pencil--between the boards before screwing them in place. The typical space used between boards is approximately one-quarter inch.
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