Composite Decking Installation and Building


Key installation videos and more below.

Building and installing composite decking is not as hard as you might think. A bit of planning and some measuring is where to start.

Below you will find some very useful instructional videos. We recommend that you watch these to get a clear idea of what is involved during the installation process. If you feel composite deck installation is beyond you or you just don’t have the time, a local carpenter or builder will breeze through the process.

How to build a composite deck
How to build a composite deck
Composite deck construction
Composite deck construction
Composite decking steps
Composite decking steps


Read this first about when your deck is delivered, basic cutting advice and safety.

Circular saw or hand saw to cut composite decking

The Build

When your composite decking boards are delivered its advisable to allow them to sit for at least a day – the reason for this is to allow them to adapt to the surrounding temperature and conditions.

It is not advisable to install composite decking in cold weather. Your composite decking boards can be worked with normal woodworking tools. It’s recommended to use a wood saw with a fine-tooth blade or a chop saw / circular saw (if you know how to use one) to cut boards to size. When cutting the composite decking boards, care should be taken to ensure that the composite boards are sufficiently supported.

As with any building work it is important to work safely and to take safety precautions including the wearing of protective clothes, gloves, safety goggles and dust mask.



Build a Supporting Substructure

Make sure that the base is flat and stable. It is not advised for decking boards to be laid directly on the ground, they should be fixed to joists of a suitable supporting substructure. This will vary depending on the use. For example for a domestic patio deck its typically advised to use a simple concrete base and WPC (wood plastic composite) joists.

The concrete base should be at least 10cm thick and have a slight slope – a suggested gradient is approximately 1 in 80 – that runs away from the property. The reason for this is to allow the water to flow away from the property. This is extremely important.

The WPC joists should be fastened to the concrete base using screws through the joists and plastic raw plugs into the concrete base. It would be advised to fix them so as to create parallel, regularly spaced rows in-line with the slope of the concrete base, which will again allow for the run-off of water.

The maximum recommended space between joist rows depends on the angle at which you intend to lay your boards in relation to the joists, but should never exceed 40cm.

Its advised to leave a minimum gap of 8mm between the ends of joists and a fixed object such as a wall and of a minimum of 10mm between the ends of joists at butt joints. The distance allows for proper drainage and temperature expansion. Each composite decking substructure can vary so its important to discuss all fixtures and fittings with the person laying the composite decking (which could be you) and the company supplying it.

Check out our FAQs – we have lots of helpful information about deck planning and installation.



Composite decking T clip

Fix Composite Decking Boards to WPC Joists

Composite decking boards should be easily fastened to the joists of a supporting substructure with the help of steel screws and plastic T-Clip systems. Each supplier will have alternative fixings available so its best to research will work for your composite decking project.

Its advisable to start at the outside of the area to be decked, place the first decking board into place and screw it into each joist it crosses with a countersunk decking screw of suitable length.

You will want to then fit T-clips into the groove along the side of the board and screw them into each supporting joists with screws. Most companies will supply screws with fixings, so check with the company before planning the build.

Fit the next composite board by sliding it onto the T-Clips if using these, follow a similar process to fix subsequent boards attaching the final board in a similar manner to your first.

As an alternative to using T-Clips, composite decking boards can also be screwed straight into supporting joists using decking screws through the center of each board. Unlike timber, composite decking only requires one screw in the center of each board as they do not warp or bow.

Decking boards must be properly supported!

Its imperative that the ends of composite decking boards must be fully supported. No overhang or cantilever is allowed. At butt joints (where the ends of two decking boards meet) this may mean doubling up on supporting joists.



Finish Your Amazing Deck

Once you have fastened your composite boards all that remains is to tidy up the sides of your new decking area. Several decking suppliers sell WPC skirting and corner trims which can be used to hide the unfinished end of boards and supporting joists. Leaving you with an attractive finished edge. You should always plan to cover the end of hollow composite decking with the correct end cap or trim – this will avoid excessive moisture ingress. Ask your supplier for more information and recommendations if you are unsure about this process.

WPC skirting trims can be screwed directly into joists with wood screws. A gap of at least 8mm should be maintained between skirting trims and the ends and sides of boards to allow for expansion due temperature increases.

Corner trims can be applied subsequent to skirting trims to achieve a finishing touch by screwing them directly into decking.

Its recommended that you do not fully close your deck to allow for the free circulation of air and drainage.

Overall, the installation process is quite easy. Any good decking supplier should provide you with an installation guide, but if not, this gives you a good idea on how to start.

  • We would like to thanks all the companies and websites for the amazing images and videos we have used on this page:

    Cladco Composite Decking
    McNicol & Butler
    UPM ProFi