Does Composite Decking Expand and Contract?

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decking expansion

One of the things that you should consider when building a deck is the expansion and contraction of the materials. But you may wonder, does composite decking expand and contract? What causes materials to do so? And why should you know these things?

What Decking Materials Expand and Contract?

The contraction and expansion of your decking boards should be one of your concerns when building a deck. Traditional wooden decking is the most prone to these changes. Other decking materials expand and contract; it is important to leave some gaps when installing them to accommodate the expansion.

One of the main reasons why this happens is because of humidity. When wooden boards are in high humidity areas, they absorb moisture. And because of that, the wood expands. It also happens when the boards are exposed to wet weather. On the other hand, wooden boards contract because of the lack of moisture. So in places where the climate is dry, it’s more likely for the boards to contract.

But here’s the question, since composites, or wood-plastic composites to be exact, are part-wood, do they expand and contract?

Do Composites Expand and Contract?

Does composite decking expand and contract

Yes, composite decking materials expand and contract in all directions, but not as much as real wood. Composites are resistant to moisture. Instead, they change in size due to temperature. It will expand when under a hot temperature while contracting in the cold. But why do you need to know whether composites or any other boards, expand and contract?

Why Is It Important to Know?

There are many reasons why you should account for the composite board’s expansion and contraction. Some of the reasons include ease of installation, safety, and deck spacing.

Makes Installation Easier

When on their normal size, composites are quite easy to work with. However, as the temperature increases, the boards expand and become pliable. This change can make the cutting and installing process difficult. The contraction of the boards also poses a problem, as you may not be able to install the boards properly.

How does this information help? When working with composites, it’s best to install them in the early morning. When the temperature gets too hot, it’s best to stop for the day and continue tomorrow. 

Safety Reasons

Another reason you should be concerned about the contraction and expansion of the boards is safety, especially when using nails and screws. When the boards contract and expand, there’s a chance for the nails and screws to move back up. This can be damaging to the deck, but it’s also a safety problem.

How can this information help? When choosing a composite, you may want to use grooved decking boards. These boards don’t require drilling or nailing on their surface. Instead, they use a series of clips and hidden fasteners to hold down the boards. On the other hand, if you’re working with ungrooved boards, you need to ensure that the nails and screws are intact to avoid unwanted accidents.

Proper Deck Board Spacing

Perhaps the most important reason you should be familiar with contraction and expansion is deck board spacing. Deck board spacing refers to the amount of space in between the boards.

Why is this important, and how can this help? Since the composite decking materials can expand and contract, installing them too close to each other can cause friction between the boards. On the other hand, installing them too far from each other can leave big gaps when the boards expand. So what should you do? 

In general, you should leave a 3mm to 6mm gap from each board. You also have to consider your location. If you live in an area with a hot climate, the boards will be more likely to shrink when the climate cools down. In this instance, you may want to shorten the gap. On the other hand, you may want to space your decking boards more if you’re living in a place where it’s always wet and humid.


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