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How much can composite decking shrink?

April 18, 2022

As temperatures fluctuate, composite deck boards will naturally experience thermal expansion and contraction. That’s why the board ends should never be installed tight against one another. So, how much can composite decking shrink? That will depend upon the air temperature at the time of installation.

When you build an outdoor decking. One of the things that you should consider 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 are decking materials expanding and contracting?

The contraction and expansion of outdoor decking boards should be one of your concerns when building a deck. Traditional wooden deckings are the most prone to these changes. Other surfacing materials will also expand and contract. So it is important to leave some gat 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 decking boards are exposed to wet weather. On the other hand, wooden boards contract because of the lack of moisture. As a result, decking materials are more likely to shrink in dry climates.

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

Do composite deck boards expand and contract?

For most composite decking there is negligible expansion and contraction in the width of the board. However, the expansion and contraction occur in the length of the composite decking board. Quality composite decking should have very minimal shrinkage if manufactured correctly.

As temperatures fluctuate, composite deck boards will naturally experience thermal expansion and contraction. That’s why the board ends should never be installed tight against one another. Then, install a fastener in the middle of each board length to prevent shifting during thermal expansion and contraction.

outdoor decking shrink | install outdoor decking boards

Do COOWIN composite deck boards shrink? Composite decking tends to grow and shrink across the length of the boards as it heats and cools. Proper spacing will allow some movement without buckling.

How much does COOWIN WPC decking shrink and expand? Composite decking is known to shrink and expand along its length, not its width. Or at least very minimally across the width. Experienced carpenters will know that this is the opposite of what natural wood does. Wood expands very little along its length – as little as 2% whereas it can expand 6-8% across its width.

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

Makes Installation Easier

When at their normal size, composites are quite easy to work with. However, as the temperature increases, the composite decking 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.

For areas that are subject to significant temperature swings. We recommend installing your deck boards using surface fasteners. First, ensure that the deck boards are aligned properly. Then, install a fastener in the middle of each board length to prevent shifting during thermal expansion and contraction.

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 outdoor 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. Not only can this 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 fasteners to hold down the boards. On the other hand, if you’re still using 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 why you should be familiar with contraction and expansion is because of deck board spacing. Deck board spacing refers to the amount of space between the boards.

Since the composite decking materials can expand and contract. So 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 would want to leave 5-8mm 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. In this case, you want to shorten the gap a little bit. 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.

author avatar
Galen Content Writer
Galen is a content creator and decorator with five years of experience designing home decor. In his daily life, Galen is constantly on the lookout for the latest, great examples of house design and further optimizes his solutions. Additionally, he writes articles related to outdoor design, interior design, and architectural decorating materials to help brands build more engaging relationships with their audiences.
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