Does composite decking expand?

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does composite decking expand

Using decking at home, particularly composite decking has become more and more popular. It serves as the perfect place to relax, bond with your family, have a sip of coffee or just sit and read your favourite book. There are two common kinds of decking such as traditional wood decks and composite decks. Given the two options, people mostly opt to go for composite wood decking mainly because of the various advantages that they can have if they go with composite decking, such as durability, little to no maintenance, resistance to environmental factors etc. There is just one question on or before the installation process of composite decking. Does composite decking expand? The answer is, yes. So, with that, you need to leave a certain space requirement for your composite decking boards to allow space for expansion.

The Reasons Why Composite Decking Expands

Thermal Expansion

Due to the composition of the materials of composite decking, it undergoes thermal expansion. Relatively high temperatures may yield the expansion of both its length and width.

Composite Decking Colour

Your chosen colour of composite decking can also affect the expansion rate of the boards. The darker the colour, the more it can absorb heat, thus leading to more expansion than that of the lighter ones. This will be a factor to consider, especially for those homeowners who have no choice since their composite decking area does not have any shade. If you want to go for the darker colour, then you can set up the frame to shade your composite decking so that it will not be too exposed to too much heat.

Location of Composite Decking

Given the fact that exposure to heat and colour can affect the expansion, you have to plan where the location of your composite decking will be. If you don’t have a naturally shaded area on the place where you want to put your composite decking, then there are various shade design ideas that you can search online to give you the best experience to prolong your composite decking.

Advisable Spacing Requirement

Different manufacturers and suppliers of composite decking will provide different instructions on the installation process as well the space and gap requirements. Generally, the expansion occurs more on the length than the width. The longer the composite decking boards you purchase, the more it will expand. There are different gap charts for each end of the composite decking products depending upon the size, especially if you have it customised to longer boards. Whatever measurements you have, the space requirement should be the same on both ends of the two composite decking boards. Below is additional information that you can take into consideration:

Joist Spacing

The space between joists should be 300 millimetres (maximum). For commercial projects with higher footfall, the joist spacing should be 200mm or lower.

Spacing between Fixed Objects such as Walls and Fences

There should be a minimum of 20 mm gap towards the walls or other fixed objects.

Height off the Ground

The composite deck must be 300 mm (minimum) off the ground when over soft ground.


There should be a drainage slope of 4 mm per meter.


Do not overhang joists at more than 20 mm.

Board Thickness

Some composite decks are available in different thicknesses. Solid lengths are recommended to have 16 inches in width, and hollow boards are highly recommended to have a 12 inches space.

Level the Joists

Level the joists at the same height and fasten them with four (4) screws for every 12 inches to ensure support to the butt joints of your composite decking. In case of the presence of a rail post, there should be a ⅛-inch space to allow space for thermal expansion. 

composite decking

The installation process of your composite decking requires careful planning and measurement right from the start. If you don’t, it can ruin the entire platform, and you will have no choice but to change the entire composite decking, and of course, nobody likes that. The main reason why people go for composite decking is that even though it requires higher initial costs compared to others, it has little to no maintenance costs that make it cost-effective during the longer term your composite decking is in service. Do not make the expansion of the decks the reason for the additional costs. A friendly reminder to always check your local building regulations (if required) and the manufacturer’s installation requirements. Different purposes may have different spacing requirements. You must be specific about will the composite decking’s use for either residential or for commercial purposes.


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