Purpose of Spacing Between Exterior Deck Floorboards

Moisture

• Moisture can make deck surfaces slippery. Standing water eventually evaporates or is absorbed into wood decking. Repeated moisture accumulation can cause individual boards to warp, twist, crack or rot. Water also leads to problems with nail head pop-ups and stains on the boards.

Dirt and Debris

• Rains often wash debris from trees, plants and everyday dirt accumulation across decks. If the gaps between boards are not large enough, debris gets trapped between boards. Besides being unsightly and difficult to clean, this debris buildup traps moisture. Over time, moisture works its way into the edges of deck boards and could rot them.

Dry Wood

• Dry wood, or deck boards that have little to no moisture content, are spaced about 1/8 inch apart. When assembling a deck, installers use a 16d nail between deck boards to approximate that distance. Dry wood does not shrink very much, so installers must incorporate the spacing during construction.

Wet Wood

• Pressure-treated lumber is typically still soaked with insect- and decay-fighting chemicals when brought to the work site. As a result, shrinkage values are high for pressure-treated decking material. Typically, these boards are butted up against one another without using a gauge for spacing because normal exposure to sun and heat will shrink the boards to achieve the proper spacing.

Composite Material

• Composites are dry and have little movement. Manufacturers make fasteners that fit in between deck boards to create the correct spacing and connect the boards to deck joists without nail or screw heads showing. Composites are also attached the traditional way with screws driven through the faces of the boards and into joists. If constructed this way, 16d nail spacing is necessary.