How To Install Composite Decking?

When installing composite decking yourself, it is extremely important to follow the installation guidelines provided by the manufacturers. This is mainly due to the thermal expansion and contraction that composite decking experiences as a part of a plastic plastics product. Composite decking will expand and shrink from summer to winter as it cools and heats up.

The correct spacing must be provided to allow movement throughout the year and lifespan of your composite decking. Before installing your composite decking it’s important to always remember 3 key points, expansion, water drainage & good airflow. Composite decking expands in the heat and contracts in the cold. Since every area in the UK has different temperatures you need to allow up to 48 hours for the composite decking boards to climatise to the weather conditions in your location and carefully take into consideration the expansion and contraction gaps required during installation.

Water drainage & good airflow are also important. This is why Ultra Decking recommends a raised deck area with up to 2.5% gradient ensuring all water drains off the deck easily and a raised deck of a minimum of 300mm. If you do choose to complete a ground level deck it’s important to allow a slope and area for the water to drain off easily, please check this during installation. Note: Please ensure that the drainage between the bases is good; otherwise, this will cause long term rot of the joists and deformation of the decking.

Important note – Don’t forget the gaps, a 25mm expansion gap should be left between the deck and any walls or fixed objects, 3mm gap side to side of all deck boards and a 6-8mm gap on any joint butt (8-10mm gap left below 10 degree) with a 6mm gap left at the end of the boards or meeting a facia or trim angle. However, it is important to double-check with the manufacturer’s installation guides to double-check.

Upon installation, one thing to note before starting your install is to open up your boards up and allow them to settle in the climate for at least 48 hours.

When storing the boards please ensure the boards are flat, covered and supported at 30 cm intervals.

Ensure you have enough materials to cover your new decking project. This is a common error due to incorrect measurements or not creating a detailed plan.

We also recommend adding at least 5% wastage to your calculation or measurements. Add at least 15% extra materials for diagonal areas due to higher wastage.


  • Always handle boards with care picking up and placing down rather than sliding and dumping, it’s recommended to carry a board on its edge.
  • Always check your calculation to ensure you have the correct amount of boards and accessories.
  • We recommend to add 5% wastage or 15% on complex and unique designs
  • Tools needed to install your composite decking: a spirit level, a power mitre saw, tape measure, an electric or manual screwdriver, a power drill, rubber mallet, dust mask, safety glasses, knee pads, plunge saw, jigsaw and a long screwdriver bit.
  • A power mitre saw is recommend for speed, accuracy and not to mention for edging and corners.
  • A 40 to 44 teeth circular saw is recommend for a neat cut.
  • Composite decking can be installed on a timber frame or composite frame
  • Using timber joists on composite decking ensure you use 4 by 2 pressure treat timber
  • Using composite joist ground level composite bearers can be used at 50 x 50, please check structure strength with a professional before purchasing
  • Anything raised Ultra decking recommend 4 by 2 timber or composite joists to ensure structure integrity
  • Post should be cemented 500m into the ground to ensure a solid frame.
  • Nogging and blocking to prevent rolling of outer joists
  • Joist hangers to be used for added support.
  • Decking joists supporting your new composite decking must be spaced no more than 30cm or 300mm. Commercial project joist centre must be 20cm or 200mm
  • Gradient must run away from any buildings or fix objects
  • Ensure 3mm gap side to side, this must be checked during installation.
  • Start clips are required to be use, placing them every 30cm to 300mm along your first joists. Starter clips are connected through the singular counter sunk whole. Use a rubber mallet to tap in to place.
  • Once your first board is in position using your starter clips, You will then need to use slim clips or you plastic fasteners.
  • Make sure that the composite decking boards do not overhang the joists by more than 15mm
  • Slim clips are connected every 30cm or 300mm by drilling through the counter sunk singular whole, remembering not to over tight.
  • Once all clips in place simply present your next board and push into place.
  • When levelling the joist, it’s important to keep the butt joists at the same height (remember to leave a 6mm end to end where two boards meet) and use 2 hidden fasteners on each side of your composite decking on the double joist.
  • To fit the final board (only when slim metal clips are being used). With the last board in place after securing all other boards, screw through the groove of the last board at an 45 degree angle, securing it to the joist at 300mm intervals, Pre-drill pilot holes in the deck boards 2-4mm wider than the width as the screw shank. Do not over drive screws into the deck boards to avoid the material splitting
  • When installing a Balustrade or railing post always ensure you leave a 6 mm gap for thermal expansion.
  • We recommend corner trims with hollow composite decking for a neat and clean finish.
  • Bullnose boards allow you to create a flush finish without adding a fascia or an angled corner trim. Its important to remember a double joist will be required and these must be installation first. To fit a bullnose board simply add starter clips into the designated location on the bottom of the board. Then slide the bullnose board into place and push forward to secure in to place with the clip ready for the next board to be laid. You can adjust the spacing of your starter clips to achieve an overhang or flush finish. To fit Ultra Decking onto steps, bullnose boards can be used. Add the decking starting from the bottom step, then place your bullnose boards into place.
  • After you have installed your new composite decking, don’t forgot composite decking is low maintenance and not no maintenance. Regular cleaning with hot soapy water and a soft brush will ensure it is free of debris, dirt and leaves. Doing this once a month throughout the composite decking’s lifespan will ensure your new composite decking is kept in good condition. Depending on weather conditions and due to the sun’s UV rays, all composite decking over time will naturally fade with a reduction in colour. Like almost all materials left to nature’s elements, your composite decking colour will lighten in appearance within the first 2 to 12 weeks (please note: depending on UV exposure). After this period the colour stabilise to its natural colour losing minimal amount of colour over the composite decking life of service. Therefore, this should be taken into consideration when choosing the colour of your new composite decking.
  • For a full detailed installation guide or our in depth video please visit our