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How to Install Composite Decking

Eelinn Vanquaethem

Created at: Jan 16, 2020

Last updated: Jan 16, 2020

Construction Curved Design Diy Garden How to: decking Landscaping Popular Technical

Building your composite deck from scratch might seem quite demanding, but with this easy-to-follow installation guide for gardens, balconies and curved decking, you will soon be enjoying your great outdoors worry-free.

It is important to note that EnviroBuild decking is compatible with various subframe materials such as treated timber, metal or plastic lumber. We recommend Manticore plastic lumber to ensure you get the maximum life span out of your garden decking.

General notes

In all cases, joist centers for the Pioneer range should be no more than 300mm and for Frontier, no more than 400mm.

Recommended tools:

  • Power mitre saw or circular saw (40 tooth alternate top bevel finish)
  • Hand drill (0.3mm and countersink drill bits)
  • Impact driver (Use T15 secure drill bit supplied in all Hyperion hidden fastening packs)
  • Jigsaw
  • Spirit level
  • Smart bit
  • Carpentry square
  • Screws
  • Tape measure
  • Safety glasses and relevant personal protection equipment
  • Chalk

When calculating the number of decking boards and accessories you’ll need, it is recommended that you add approximately 5% to the total material required for a wastage factor. It is unlikely you will use the board lengths perfectly on your balcony.

If you are planning to diagonally lay your decking, you will likely generate more scrap from cutting; in that case, it is recommended that you add 15% extra material.

To find out how much decking you should order, use our calculator or contact our team who’ll be happy to help.

Prior to screwing into composite products, we also recommend that the correct sized pilot holes are pre-drilled. The length of the hole must at least be the same length as the screw.


Step 1: Preparation of the Deck

On soft ground, post supports are recommended to support your deck.

Ensure that:

  • Any top turf layer is removed, and scree or gravel is laid to aid drainage
  • A drainage slop of 4mm per meter is incorporated
  • Composite decking is installed at a minimum of 300mm of the ground
  • Foundations are higher than surrounding areas to avoid ponding

Step 2: Building the Deck Sub-structure

Placing a decking substructure on soft ground

Recommended Materials:

  • Plastic Joists
  • Posts


  1. Cement your posts at a minimum of 500mm (or 1/3 of the total post height) into the ground
  2. Attach the joist frame using good quality galvanised mushroom capped bolts which penetrate both the bearer and the upright post

Ensure that:

  • Each bearer or joist is supported in a minimum of 3 places
  • Bolt holes are oversized by 3mm to allow for expansion when using plastic lumber
  • A 10mm gap is left where the joist end meets a cross beam when using plastic lumber
  • At butt joints, the deck boards ends do not share a single joist


  • Use joist hangers to hold joists to cross beams to strengthen the deck and reduce the number of posts required.

Step 3: Laying the deck 

Laying decking on substructures in gardens

Recommended materials:

  • Starter fasteners
  • Hidden fasteners


  1. The first board must be fixed with a hidden starter fastener through the side groove of the boards: align the starter fasteners along the first joist, securely screw each fastener to the joist then simply clip the first decking board to the starter fasteners.
  2. To fix adjacent boards, place the hidden secure fasteners into the grooved edge of the board you just fixed in place and secure screw into the hidden fasteners. Ensure that screw holes are lined up with the centre of the joist and one fastener is used per board at butt joints. One hidden fastener should be inserted at each joist and used at board ends. 
  3. Place the next plank into position against the hidden fasteners: slightly raise the outer edge of the plank being installed and slide it onto the hidden fastener ensuring that the decking plank contacts the spacer tab. Lightly tap into position if required.
  4. Tighten the screws through the hidden secure fasteners and into the joist
  5. Apply sideward pressure on the decking to ensure that the tabs are hard up against the inside of the decking groove
  6. Repeat this method until you reach the final two boards.
  7. Mark on the last joist where the edge of the final board would lie, knowing the width of the last 2 boards including the spacing gap in between them.
  8. Using these marks, attach the hidden starter fasteners securely to the end joist for the end board.
  9. With the final board in place, insert the penultimate board against the last set of hidden fasteners. With the 2 boards in place and enough of a gap between them for the fasteners, slide down the required number of hidden fasteners & secure.

Finished Pioneer walnut decking


Step 1: Preparation of the deck

The height of the decking will be determined by the depth of your balcony. Your deck should be neither lower than the tip of your balcony, nor exceeding it. Accordingly, the depth of your terrace will determine the type of pedestals and substructure that need to be fitted underneath the deck.

Ensure that:

  • A minimum 20mm gap is left where your deck abuts walls or other fixed objects
  • Decking boards do not overhang joists by more than 20mm
  • There is a deck slope of min. 5mm per meter towards a drainage area
  • The deck is not laid directly onto any surfaces, and that you leave at least 50mm beneath the deck for air circulation
  • You measure twice and cut once!

Step 2: Building the Deck Sub-structure

Laying a substructure for decking on balconies

Recommended Materials:


  1. Lay the pads onto the balcony surface.
  2. Place the pedestals on the top of the mats.
  3. Lay the joists on top of the pedestals. Ensure that the distance between joists is no more than 300mm apart for the Pioneer range and 400mm apart for the Frontier range. Joists should also be doubled up for butt joints cross the deck. Each joist should also be supported in a minimum of 3 places (joists need to be supported to the following maximum spans: 50 x 50   mm profile at max. 500   mm intervals, 50 x 100 mm profile at max. 750   mm intervals, 150 mm profile at max. 1500 mm intervals) and should not overhang support by more than 50mm. Ensure that deck boards run perpendicular to the joists as well. 
  4. Screw down the joist cradles to the plastic lumber (make sure to leave an expansion gap of 6mm between the joists).
  5. Adjust the height of the pedestals accordingly, making sure that each of them supports the joist. This can be most easily achieved by setting out each end, and then extending the pedestal until it is touching the joist. The joist shouldn't bounce over a pedestal at all.

Step 3: Laying the Deck

Laying decking on a substructure for balconies

Recommended Materials:

  • Starter Fasteners
  • Hidden Fasteners


  1. Screw down the starter fasteners into the outside edge of the outer joist.
  2. Slide the first decking board towards the clips and secure. Decking boards should be gapped at a minimum of 3mm side to side. This is dictated by the size of the clip that you use and doesn't need to be measured.
  3. Tilt the decking board up slightly and screw down the fastener. Insert one hidden fastener at each joist. The hidden fasteners shown leave a 6mm gap between the decking boards.
  4. Install the second row of decking boards. In any row where butt joints are required, make sure to leave an 8mm expansion gap. Failure to leave a gap can result in undue strain on the decking boards as they try to expand, and potentially eventually splitting. Always use one fastener per decking board at butt joints.
  5. Screw down the second hidden fastener, in order to secure the second row of decking boards.
  6. Return to tighten up the first row of decking boards.
  7. Repeat for the rest of the decking boards, up to the last two boards.
  8. Attach the hidden starter fasteners securely to the end joist for the last decking board, and then place the penultimate board.
  9. Slide the fastener between the last and the second to last decking board over the joist, and screw down.

Finished balcony decking

Finishing touches for garden and balcony decking

Recommended Materials:

  • Fascia Board
  • Corner Trims


  1. Screw the fascia board to the joists, in order to hide the grooved decking edge.
  2. Add any corner trims (provided only for the Pioneer range).

Creating a circular deck

At EnviroBuild we are often asked how to install a variety of shapes for decking and especially customers who are very capable with a circular saw wonder whether they can install a circular deck.

They undoubtedly look beautiful and become a real feature in a garden.  However, no amount of cutting will get a perfect curve that doesn't require finishing without looking untidy.

Wild Wood at Goat Lees Primary School in the Hyperion Slate Composite Decking Frontier Range

The easiest way to create a curved edge is to use the composite fascia boards. These are thin and flexible enough that they will bend.


  1. Prior to building the substructure, measure around the inside of the curve and ensure the substructure is in place at regular enough intervals to hold the fascia to the curve.
  2. Build the substructure and decking using the method used for garden decking. The decking boards will need to be curved using a circular saw.
  3. Once the decking is fully laid, start at one end and apply a constant force onto the fascia boards. This is very much a two-person job, particularly if the bend is acute.
  4. Screw the fascia into the substructure using a standard countersunk wood screw.
  5. Workaround the bend that you are intending using the same technique.


This may be a tricky process, but the result is magnificent and can transform the look of a garden. It works with either of the Hyperion Composite Decking ranges that we stock.

Finished circular Pioneer oak deck

Another method of making a circular deck is by heating the boards. Due to the plastic content, they will become softer and easier to bend to a variety of shapes. There are YouTube videos available on how to do this, however, it is technically difficult to do without damaging the boards. It also requires expensive specialist equipment and doesn't give significantly better results, thus we do not recommend this option.


More detailed guidelines can be found here. Our team of experts is also happy to advise you in any way possible to ensure your project is smooth from start to finish.  You can also call us on +353 (1) 447 0406 or send an email to ie.info@envirobuild.com.

We hope that you’ll enjoy your deck!