Composite decking is a strong and durable building material that is used to install decks. Composite decking is made from recycled wood and plastics, so no trees are fallen to make the boards.

The wood and plastics are then processed in factories and cut into various sizes so that they can be used for building decks. The boards, when ready, will form one of the strongest deck materials that you can use to build beautiful decking flooring in your home.

Homeowners prefer composite decking because of the ease that comes with maintaining it. This is because there is no need for you to sand and oil composite decking when installed to preserve them. 

Also, composite decking is more desirable than timber decks and will not wane when they are exposed to the ultraviolet rays of the sun. The installation process of composite decks is easy because you can choose between the surface installation and the hidden installation.

When installing composite decks, there are procedures that you must follow to make the process simple and to stick to best practices. One of those guidelines is to leave enough space between the composite decking board to accommodate expansion. The section below explains why composite decking expands. 

Why Plastic-Wood Decking Expands

Composite decking expands because of a change in the temperature of the location they are installed. High temperature makes it expand along its length and width.

Also, its expansion depends on the materials that are used in manufacturing it.

One thing to pay attention to is thermal expansion. This factor can make the boards shift from where they are fixed if enough space is not allowed between them.

Consequently, this leads to a situation where your decking will be weakened. So, make sure to check with your composite decking board maker for advice so that you will know the expansion level of the product. 

Other Factors that Affect Composite Decking Expansion

Other factors can affect composite decking expansion. These are the board’s colour and the location where your decking is installed. 

1 Color of the Composite Decking

The colour of your composite decking matters because it affects how it expands.

This is because dark-coloured composite decking boards absorb more heat than light-coloured ones. Dark brown boards, for example, will absorb more heat than light brown composite decks. 

When this happens, the dark-coloured composite decking will expand more than the light-coloured one. So, if you live in a hot environment, it is recommended that you choose light-coloured decking boards.

2 Location of Decking

Composite decking boards exposed to direct sunlight absorb heat more than those positioned under shade.

This means that composite decks built in the garden or lawn will absorb more heat than those built on the balcony.

Plastic-Wood Decking Gap

When installing your deck, you should not allow your composite decking board to meet at both ends.

You have to leave a space between the boards. This is to accommodate the composite decking expansion gap.

The essence of leaving this space is for the decking to expand and contract when they heat up. 

The amount of space required depends on how often the temperature changes where you live.

If you reside in hot regions that have frequent temperature changes, you need to leave a larger gap than you would if you live in a region where the temperature doesn’t change so often. 

Different manufacturers and suppliers of composite decking will provide various instructions on how to install your deck and the right amount of space that you should leave.

Here at Composite Warehouse, we recommend that there should be a 5mm gap between the ends of your composite decking boards. 

So, when you are laying your boards on the joists, you must make sure that you leave at least 5mm space between them. 

This is so that when the composite decking expands, the decks will not wrap.


Composite decking expands when it is heated or exposed to direct sunlight. So, it is advised that you leave a space of 5mm between the edges of the decks.