Does Composite Decking Expand And Contract?

By Galen |

Traditional wood decking can experience thermal expansion and contraction when experiencing temperature changes. So, as the best alternative to wood decking, do composite decking boards expand and contract? The answer is yes, like most solids, composite decking boards expand and contract slightly when temperatures change. Material scientists have found that composite decking materials have a low coefficient of thermal expansion.

This property of composite decking boards is well known and can easily be avoided when building decks that have problems with board expansion. In fact, this property complements the other benefits of high-quality composite decking. For example, consistency from one board to the next, ease of maintenance, and longevity. Additionally, unlike traditional wood, composite decking will not expand or contract when wet.

Read on to find out how much composite decking boards expand and contract. Also, we need to understand how to adjust the spaces between decking boards to accommodate expansion and contraction.

What Causes Composite Decking to Expand or Contract?

Most things expand and contract when the temperature changes. This is because molecules move faster or slower. Water also changes the dimensions of boards made of certain materials, such as wood.

Causes of Expansion

Heat. When the temperature rises, the molecules in composite decking boards move around and collide with each other, making the space they occupy larger. The decking boards will “swell” a bit as a result.

Too much water. Too much water won’t affect composite decking much, especially if it has a PVC shell that won’t let water through. Because of this, composite decks can easily handle rain, snow, and temperature changes. Wooden decking, on the other hand, is porous, so once it gets wet, it absorbs water and expands.

Causes of Shrinkage

Low Temperature. When the temperature drops, composite decking boards cool down and shrink slightly. And, this shrinkage is very small.

Low humidity. Composite decking boards are largely unaffected by moisture, but natural wood loses water easily in dry climates. As a result, the wood fibers shrink, which causes the deck to dry out and crack.


How Much Does Composite Decking Expand?

When it comes to expansion and contraction, different brands and types of composite decking behave differently. For the most part, composite decking boards expand between 0.1% and 0.3% of the length of the boards. It is important to note that the width of the boards will also expand, but with standard longitudinal drainage spaces, this is not a big deal.

The composite decking manufacturer recommends that all butt joints and mitered joints should have a gap between them so that the composite decking boards can expand and contract from end to end. The recommended amount of decking clearance will vary depending on the temperature of the location where the decking is installed.

If composite decking boards are installed at temperatures above 40°F, there should be a 1/8″ gap at the butt joints. If the installation temperature is below 40°F, the gap should be 3/16 inch.

Most composite decking boards have the same clearance. Check the manufacturer’s instructions and specifications. Mineral-based composite decking does not expand and contract like standard composite decking, so it can be installed without an expansion gap.


Is the Expansion and Contraction of Composite Decking Worth Worrying About?

Anyone who owns a home should know how composite decking performs. But that doesn’t stop you from enjoying your outdoor space. Just make sure you take this into account when laying your deck yourself. You can also ask the person building the deck what they plan to do with it.

Using the longest boards you can find (usually 16 or 20 feet) is another way to reduce butt joints and the gaps you need to leave. One way to reduce end-to-end seams and gaps is to use picture frames and vertical transition boards, also known as “breaker boards.” This reduces the number of places on the deck where dirt and other things can be collected. With less debris on the deck, there is less opportunity for mold to grow.

Composite decking materials are great for use around pools and hot tubs because they don’t absorb as much water. Pressure-treated wood framing underneath the deck will still expand and contract when wet. To prevent water and moisture from entering the deck’s substructure, we recommend that you apply waterproof tape to the joists.


How to Install Deck Boards in the Right Place

Most deck boards are spaced apart for good drainage and air circulation. And these gaps prevent tree chips, dirt, and other debris from accumulating on the deck. If hidden fasteners are used, then the spacing between the planks on either side is already established.

However, when the ends of two planks meet in a butt or miter joint, you need to make sure there is enough expansion clearance to handle changes in temperature. If you don’t leave enough clearance between the planks when you install them. Then when the temperature rises, they may touch each other and expand.

This could loosen the screws holding them in place and cause the planks to warp. In addition, to make sure your warranty is valid, you must install the product exactly as the manufacturer intended.

Here’s how to install it correctly:

Use the Correct Measurements

It is very important to measure and cut correctly. For best results, measure the entire length of the area where the boards will be located and then remove the space you want to leave.


Using a Jig

Using a tape measure to set or check plank spacing is both time-consuming and inaccurate. Therefore, avoid using a tape measure and instead use jigs or spacers. You can buy gauges in different sizes or you can use nails, coins, pencils, or any other hard object of suitable thickness. Different thicknesses can be used to vary the distance as required.

Consider the Weather

When the weather is hot, the length of the planks will become longer. In cold weather, the length becomes shorter. Therefore, if it is cold outside, it may be necessary to allow more space at the joints. If it is hot outside, the opposite may be necessary. Direct sunlight can cause the boards to absorb more heat than you think, even if the weather is nice.

It’s not only when laying composite decking that you need to consider expansion spacing. You should also consider expansion spacing when adding composite fascia boards and railings, as well as built-ins such as pergolas and benches. In addition, composite cladding (siding) should follow the manufacturer’s installation guidelines.


To Summarize

In addition to being heat and water-resistant, composite decking materials are superior to wood and PVC decking in many other ways. For example, they last longer, require less maintenance than wood, and are very consistent from board to board.

If you’re interested in these low-maintenance composite decking, contact our service team for a free sample.

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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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