What size Gap is Required Between Decking Boards?

M. John

Spacing is important in deck building. Failure to leave gaps between your ultra decking boards can cause damage to the board as well as the deck frame. Proper spacing allows for expansion and contraction,  proper drainage and helps to keep the decking framework dry.


Factors That Influence a Decking Size Gap

Spaces shown as gaps in between a a complete sitting composite decking floor
Composite decks that have considerable size gaps last longer than those that do not…
There are things to consider when spacing your decking. They include wood type, moisture level and also the type of fasteners. These will help you determine what size gaps are required between the decking boards.

Wood Type

The kind of wood you choose for your decking can determine the size gap between the decking boards. It would be best to consider the properties of the wood you want to use for your decking. Pressure-treated wood, hardwood and wood like cedar and redwood absorb moisture differently with different expanding and contracting properties.

Moisture Level

If you are using wood decking, you need to consider the moisture level of the wood to know the size gap between the decking boards. Wood deckings with high moisture content will expand more when compared with the ones with less moisture.

During summer, wood decking will expand due to high moisture levels. While in winter, the decking will contract due to low humidity, thereby reducing in size. With this in mind, while installing wood decking, leave a slight gap between the decking boards since the decking will contract in winter, thereby creating a larger gap. Same with summer, you also need to leave a little gap to allow for expansion.


The kind of fasteners you use for your decking can also affect the size gap between the decking boards.

You should consider using screws to hold your decking in place instead of nails. Screws tend to grip the decking stronger, thereby keeping the board in place when it expands and contracts. You should have enough screws to attach the decking boards to the joist.

Is the Size Gap Required Between Decking Boards?

Depending on your region, you must check your local building code before deciding on the size gap required for decking boards.

However, the acceptable size gaps required between decking boards should be between ⅛ inch and ¼ inch. The deck board spacing should have a gap size of ⅛ inch after the decking has dried out. The ⅛ inch size gap between the deckings allows you to walk safely on your deck without tripping. Likewise, the ¼ inch also allows for proper water drainage and increased aeration.

The size gap between composite deck boards is just as important as it is with wood decking. Composite decking boards also expand and contract when there is a temperature change. When installing your composite decking, you should leave at least a gap of ⅛ inch between the decking boards.

If you install your decking using pressure-treated wood, you should leave no gap between the decking. This is because when the decking dries, the board will shrink, leaving a gap between the deckings.

If you use cedarwood as your decking board, you can space it with a size gap between ⅛ inch and ¼ inch. Dry cedar boards require a gap size of ¼ inch apart. This allows the decking to expand and contract without getting cracked. The same goes with redwood; consider how dry the wood is before deciding whether to use a size gap of ¼ inch or ⅛ inch.


The size gap required between the decking boards should be ⅛ and ¼ inches. Depending on your region, always check your local building code before choosing a  size gap for your decking boards.


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