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A Beginners’ Guide to Installing Trex Composite Decking
A Beginners’ Guide to Installing Trex Composite Decking

For many of us, our gardens have become a refuge this past year.

They are a safe haven to see our friends and family and a quiet place to take a break from the stresses of life.

As a result, there has been a surge in demand for our line of Trex Composite Decking and we’ve also seen more of our customers opting to install their own decking.

So, if you’re thinking about installing your own Trex Composite Decking area for the first time, here’s our beginners guide to going it alone.  


Straight forward

Designer-friendly Trex Composite Decking incorporates many unique features which make it quick and easy to install. There are however some differences in behaviour between wood and composite, so it is important to follow the manufacturer’s installation guidelines to ensure your deck achieves the industry leading Trex warranty. 

It will also deliver a beautiful and long-lasting decking area, which looks just like timber, but with many advantages over real wood.

Trex decking comes in a range of colours, so you can create an attractive and eye-catching picture framing effect.

When starting out it’s important to understand that the quality of the substructure is fundamental to installing the deck successfully.

Trex Composite Decking can be installed on a timber, aluminium or steel sub frame, but it cannot be installed on to a floating sub structure.

The joist centres should be a maximum of 400mm for residential installation and a maximum of 300m for commercial installation.

When planning a unique pattern, the framing will need to be adjusted to support the surface pattern.

If installing decking on to a timber substructure, you should use decking tape to prevent moisture ingress where the screw is inserted into the top of the timber such as Trex Protect joist self-adhesive butyl tape.

You should also use an end coat preservative treatment to protect the ends of the timber where it has been cut.


Installing the boards

You’ll be pleased to know that Trex is a very easy decking to system to use. It’s made of recycled plastic and wood pulp, so like all composite products, it will contract and expand in all directions.

If you see boards curving or bowing before they are laid don’t worry – this is characteristic of the product and completely natural. This will not cause any problems when it comes to installing the boards.

Should you find a board which is particularly curved or bowed, install the board at each end first. Then simply work towards the middle of the board and push it into place.

When manufactured, Trex decking boards are machine cut during warm condition, so it’s best practice to trim either end of the board by a minimum of 5mm to give a neat and square cut before installation.


Mixing it up

A common mistake is to simply lay the boards in the order that they come out of the pack. As every Trex board is unique, you should mix and match the different tones to ensure the best final look.

The Trex range includes grooved boards which are the most popular for the bulk of the deck, because they can be ‘secret fixed’ for a clean screwless finish.

Any visible edges of a deck will require a square edged board which has a neater, more decorative finish. These are used as perimeter boards and also for steps.  

When you’re ready to install Trex grooved boards, Trex starter clips need to be used to install the first or last groove board.

Starter clips are right angled and screw directly into the joist. You then offer up the deck boards to the clips.

The universal clip is the best way to install a grooved board because it provides a screwless finish and provides a consistent 6mm gapping.

This clip secures two boards together if you screw downwards into the joist. One clip should be used over every joist.

It’s important that you fix each board with a universal clip as close to the end as possible. The clip should be no more than a maximum of 25mm from the end of the board.

Don’t span the ends of two boards with only one clip. If necessary, add a piece of timber to create a sister joist and ensure you can fit the end clip properly.

We would advise loosely installing the universal clip along a row. This will allow you to fix the adjoining board when you reach the next row.

Afterwards you can return to the row to tighten up the universal clip when several rows are installed.

Square edged boards

The square edged boards can be used to create a perimeter or picture frame border. As well as adding to the design of the deck, it is the only way to ensure that exposed/visible edges are neatly finished.  Note that the Trex system does not include secondary capping trims which are not only unsightly, but can also become a trip hazard.

Perimeter boards must be face fixed. Colour head screws are available to suit all Trex board colour options.  For the Trex Transcend range, we recommend using the ProPlug Fixings System which incorporates a countersunk tool, a screw and colour matched plug. These innovative fasteners ensure the fixing point is almost invisible once you’ve finished your masterpiece.


Mind the gap

The mistake we hear about the most often at Southern Sheeting is failing to leave enough space when installing the boards so that they are butted up against one another.

These gaps are important because they will help drainage and they also allow room for the boards to naturally expand and contract.

Make sure you:

  • Leave a gap of between 3mm and 5mm at the end of every board.
  • Leave a 6mm gap at the side of every board.
  • Leave a gap of 6mm to 13mm when butting up boards against a fixed object such as the wall of your home.

If you’re using the secret fixing, the 6mm side gap is automatically provided when you use the secret fixing system.


Southern Sheeting’s top considerations for a successful decking installation are:

  • Always ensure correct end gapping (this includes mitred corners)
  • Never over-span joist centres of your sub-frame (400mm max on domestic projects)
  • Never use just one fixing clip to secure two boards at a butt joint
  • Cut the ends of the boards before installation

The great news is that Trex Composite Decking comes with a guarantee of 25 years for residential use, so won’t need to replace it any time soon.

You might put a lot of hard work in learning how to install your decking for the first time, but after that this product is hassle and almost maintenance free.

As the world no.1 decking brand, Trex features the most surface finish of any composite decking product on the market. The hard-wearing plastic cap is fade, stain, mould and scratch resistant. The boards themselves will not rot, twist or splinter and you’ll never need to re-paint or stain them again.

Having a well installed, high quality and low maintenance deck installed at your property will also be a major selling point for your home, both for visitors and for when you decide to sell it.

It has also has fantastic eco credentials: Trex hasn’t felled a single tree to create its decking in its 20-year history.

Composite materials are also less slippery when wet making them a much safer option for children.

The full installation guide is available from Southern Sheeting.

Now that you have all this information, you’re ready to start planning your first composite decking project!

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