Do You Leave A Gap Between Composite Deck Boards?


Composite decking might be one of the most convenient decking types to have outside your home in terms of maintenance, but you need to know how to install it properly. 

Composite Decking with a Sapcer to Create a Gap

One of the biggest questions homeowners have when it comes to installing their composite decking is whether or not you need to leave a gap between composite boards.

There are many factors you need to take into consideration regarding the spacing of your composite deck boards.

In this guide, we’ll be walking you through the process of installing your composite decking with the correct spacing between the boards. 

Should You Leave Gaps Between Composite Deck Boards?

The short answer to the question of whether you need to leave gaps between the boards of your composite decking is yes. 

If you don’t leave enough space between individual boards in your composite decking, you could end up with some problems down the line.

Therefore, ensuring that there is a decent-sized gap between the composite boards in your deck is essential. 

Reasons To Space Out Your Composite Deck Boards 

If you’re wondering why it matters whether or not you leave gaps between your composite deck boards, there are actually two main reasons why doing so is important:

Accommodates Expansion And Contraction 

First of all, something you have to take into account (ideally, before you even purchase the boards for your deck) is that composite decking expands and contracts significantly depending on the temperature. 

Sometimes, exposure to moisture can also cause composite boards to expand, but most of the time, composite material expands and contracts due to heat or cold. This is known as ‘breathing’. 

Leaving space between the composite boards in your decking means that the boards have enough room to expand and shrink. 

Many homeowners make the mistake of not leaving gaps in their composite deck the first time they attempt an installation.

This can lead to friction damage when the boards eventually expand and rub against one another. 

Alternatively, the expansion can cause so much pressure that the boards start to rise, warp, or crack.

Obviously, this isn’t what you want when you’re trying to build a stable, durable deck. 

Allows For Water Drainage

Another reason why you need to make sure you’re leaving enough space between the boards in your composite deck is that you need any water to have room to drain through the boards.

Spacing your composite boards too close together will prevent water from draining through, and instead, it will get stuck and collect between the boards.

This can be very damaging because trapped water is a breeding ground for mould as well as mildew.

The boards can also start to soak up the moisture and begin to warp.  

Installing Composite Deck Boards With Gaps 

Composite Deck Boards Sapced For Expansion and Contraction

Now that you know how important it is to leave gaps between the boards in your composite decking, you may be wondering how to actually space out your composite boards properly. 

There are a few factors you need to consider when determining how far apart your composite boards should be spaced, including:

End-To-End VS. Side-To-Side Spacing 

There are two different ways to space out your composite boards when building a deck. One is called end-to-end spacing while the other is known as side-to-side spacing. 

End-to-end spacing requires a gap of between 3/16″ – 1/2″ (6 and 13 mm) between boards, whereas side-to-side spacing doesn’t need such a big gap.

If you’re working with side-to-side spacing, you only need to leave a gap of 3/16″ – 3/8″ (6 to 10mm). 

Hot VS. Cold Weather 

As we mentioned earlier, composite boards will expand and shrink according to the temperature. 

Not only does this mean you need to leave enough room for future expansion and contraction when you space out your boards, but you also need to consider what the current weather conditions are like. 

The first thing you should do when you receive your composite boards leave them for 48 hours to allow them to climatize.

It can be tempting to start the installation process straight away, especially if you’ve been anticipating building your new deck for a while. 

However, leaving the boards exposed to the current weather conditions means they’ll expand or contract accordingly, minimizing the amount of guesswork you need to do. 

If, for example, the current temperature where you live is below freezing, you should leave a gap larger than 3/8″ (10 mm) between boards.

*Builder Tip*

Do not cut composite decking to be installed later. The change of tmeperature will shorten or lengthen the board if its not screwed down.

This is because the boards will currently be in a shrunken state due to the cold weather, but when the temperatures rise again, the boards will expand significantly. 

Bear in mind that if you ask composite board suppliers, they’re likely to caution against building your deck while it’s very cold in case of dramatic expansion in the warmer weather.

Of course, this may not be an option for everyone, but if you can, try to wait for more temperate weather before you start building your deck. 

Screws VS. Clips VS. Nails

You have a few different options for how to secure your deck boards in place when working with composite decking.

The main choices are screws, clips, and nails. 

We don’t recommend using nails to hold your boards in place because nails don’t provide much grip and you’re more likely to see lifting and warping when the boards start to expand. 

Screws are a better option than nails because they grip the composite material more strongly.

However, overall, we would recommend using clip fasteners because you can purchase composite clips in different sizes, mostly 3/16″ – 3/8″ (6 to 10mm). 

Brands of composite deckingOpens in a new tab. will often have recommended clip fasteners which will provide their recommended spacing. Plus often using other clips will void their warranty.

For example,

  • TimberTech = CONCEALoc®
  • Trex = Trex Hideaway®
  • Fiberon = Fiberon® Phantom®

Using these clips ensures you always have enough space between your composite boards without the need for exact measurements. Do still frequently check as you are installing the decking that the board’s spacing is consistent, and if it’s not, make minor adjustments to correct the gapping.

However, bear in mind that you’ll still need to use a screw to fix the final composite board in place at the edge. 

Frequently Asked Questions 

Can Composite Decking Be Laid Without Gaps?

Composite decking should not be laid without gaps because spacing the boards too close together will cause friction damage and even cracking due to the pressure of expansion.

Water damage and mould can also occur if moisture gets trapped between the boards.

What To Do If Your Composite Deck Boards Are Too Close Together?

You will need to unscrew the decking and re-install it with the correct side-to-side spacing and end butts. Unlike wood decking that can be ripped to the correct size composite decking will not look good with rough cut edges in the middle of the deck. As much as possible hide rip cuts under the flashing etc.

Can I Seal the Space Between Composite Deck Boards?

No, it is not recommended to seal the gaps between composite deck boards.

The gaps are there for a reason, and sealing them will prevent free expansion and contraction. 

If you want to create a dry space under your composite deck one option is Dexedry flanges. The rubber flanges are installed into the groove of the decking. Channelling water but still allowing the composite to expand and contract. But using Dexecdry will require face screwing. I would recommend cortex plugs to maintain the beauty of the decking.

Final Thoughts 

It’s very important to leave gaps between the composite boards of your decking.

This is because composite boards expand and contract as temperatures change, and not leaving gaps can cause the boards to press together and get damaged. 

Not leaving space between boards also leads to mould problems and water damage because of moisture getting trapped. 

Always take the current temperature into consideration when installing composite decking and leave a minimum of 3 mm of space (up to 8 mm for end-to-end spacing) between your boards to allow for expansion and contraction as the temperature fluctuates.

Ryan Nickel

A Red Seal carpenter, passionate about building decks to be enjoyed.

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