How To Lay Composite Decking On Soil

The many benefits of composite decking include its low maintenance, durability, and excellent lifespan, and all of these reasons make it the perfect decking material for UK gardens.

If you are interested in installing composite decking in your garden, this guide will provide you with all the information you need to install it on soil.

With so many different garden types in the UK, you must research how your composite deck boards should be installed. Proper installation will provide a long-lasting, safe decking area for you and your family to enjoy for years.



Before starting a composite decking installation project, you must prepare for it thoroughly.

Proper preparation will minimise the risk of issues occurring during the installation and increase safety.


Planning Permission

Checking with your local planning authority can benefit anyone installing composite decking in their garden. Failure to get planning permission for projects can result in fines, imprisonment, and the decking being removed.

Decking installation in the UK does not typically require planning permission if a raised deck is no more than 30 cm from the ground or does not cover over 50% (combined with other external buildings or extensions) of your garden.


Composite Decking Material, Tools & Accessories

To install composite decking on soil, the following materials may be necessary;

Site preparation

  • Tape measure
  • Spirit level
  • String
  • Pins
  • Edger
  • Club hammer
  • Spade
  • Gravel
  • Pegs and fabric for weed control


If you are planning on making and using concrete pads for the subframe to sit on, you will need;

  • Quick-drying concrete
  • Damp-proof course
  • Brick trowel


Timber Subframe Installation and Deck Board Preparation

  • 8 or 10mm coach screws
  • 8 or 10mm coach bolts
  • Combi drill
  • Socket set
  • Decking joists
  • Pencil
  • Panel saw
  • Mitre saw
  • Jigsaw
  • Circular saw
  • Sandpaper
  • Workbench
  • Combination square
  • End grain protector
  • Paintbrush


Composite Decking Installation

Buying high-quality composite decking from a trusted supplier like Ecoscape will ensure you are provided with the necessary decking boards and accessories, which include;

  • Composite Decking Boards
  • Starter Clips
  • Finish Clips
  • Hidden Fasteners
  • Hidden T Clip and Screws
  • Locking Clip and Screws
  • Angle Fascia Trim
  • Flat Decking Trim
  • Composite Edge Board
  • Screws



Choosing the position of your decking will determine ease of access, how much sun you will get, and what kind of surface it will be laid on.

Installation on flat surfaces will be easier, but decking subframes can be designed for uneven or steep areas to create a level platform to install your decking.

You should consider what positions could result in the decking area being overlooked by neighbouring properties.

Working around existing garden features, trees, or buildings should also be taken into consideration.


Safety Procedures

When installing decking, safety should be a priority. The safety of the deck after installation will require a solid subframe and the installer to follow the supplier’s installation guidelines.

Safety during the installation process is also vital.

You should not start a DIY project like this without someone else present to assist you with awkward processes and minimise the risk of harm or injury.

Checking for pipes and wires before digging is essential to the preparation process. Failure to do this could result in costly or dangerous accidents.

If you are cutting deck boards or timber for your subframe, this should always be done on a flat surface that is well-ventilated.

You must also wear suitable PPE during the process. Your protective kit should include;

  • Protective gloves
  • Safety Goggles or Face Shield
  • Dust Mask
  • Knee Pads
  • Ear Protectors


Preparing The Area

Preparing the area before installation should start with you marking out the area with string and pegs. You should then dig the soil down to a level depth of 50mm. An edger can be used to cut turf accurately.

The next step involves covering the area with a fabric to control weed growth. Some people may choose to lay concrete at this stage. Alternatively, paving slabs can be used.

If you place paving slabs for the subframe to be built on, a spirit level should be used to ensure they are all level with one another.


Build a Solid Decking Subframe

When Concrete pads should be positioned to support the deck joists, you should dig 150 mm x 150 mm squares at a depth of 150 mm around the deck in the correct positions.

Quick drying cement should be used to fill the holes, and a spirit level and brick trowel should be used to ensure they are level before they are fully dry.

The area can then be covered with your weed control fabric, with areas cut out for the concrete pads. After laying the fabric, cover it with gravel to a depth of 50 mm. A damp proof course should be used between the deck joists and concrete.

When constructing your decking frame, the framework should run across how your composite deck boards are to be laid.

The outer joists of the deck frame will be at right angles to your inner joists and should be marked with a pencil to align the outer joist’s centre.

Your coach screws should go in these marks, and there will be eight in total. A flat wood drill bit should be used to drill a recess into the mark at the screw’s head’s depth, and they should be wide enough to be tightened by a socket attachment or ratchet.

This will ensure the joist surface and screw heads are flush.

You can then line up your adjoining outer joists and drill through the recessed centre into the adjacent outer joist from the outer joist. You should use a thinner drill bit that is narrower than the coach screw shank.

This will minimise the risk of the wood splitting and helps to guide the screws.

Coach screws can now be fitted using a socket attachment or drill driver.

You can secure the inner joists after the outer frame is secured. You will repeat the process to do this, and the spacing of the inner joists will be closer together because composite is a heavier material than timber decking.


Subframe Materials

Different subframe materials offer different qualities, which should be considered before you start.

Timber deck frames are the most common because they are low-priced and easy to work with.

Timber subframes will need to be treated to last a long time, and pressure-treated wood is advised for additional strength.

Joist tape can help to protect the timber from moisture and improve its longevity.

Composite subframes offer similar qualities as composite deck boards. It is a long-lasting option that requires minimal upkeep.

Aluminium is the strongest option and will not be affected by moisture. This is a great option as composite decking is a heavy material and requires additional joists that are positioned closer together with other materials.

Plastic is the final subframe material and is long-lasting. Because it is not as strong as other options, additional supports are required, which can increase the price.


Lay the Composite Decking

You may have to cut some boards to fit the desired area when laying decking, which should be done with the utmost care. Always ensure protective clothing is worn and measurements are double-checked before starting.

The exact process of installing composite decking will differ by the supplier. You should always follow the supplier installation guide process and use the accessories provided.

Failure to do this can lead to a poorly installed deck and an invalidated warranty. For more information on how to install an Ecoscape composite decking board, visit the installation guide PDF.

Your composite deck boards must be installed with adequate gaps between the boards and adjoining walls. This is to allow for thermal expansion.

Failure to leave gaps when installing composite deck boards can result in warping and poor drainage and ventilation.



Does Composite decking need a handrail?

Raised composite deck areas over 60 cm in height will require handrails.

Planning is required for structures over 30 cm, and plans submitted at double this height and above without a handrail will be rejected on safety grounds.

Handrails, balustrades, and fencing should be considered for anyone with young children to ensure they can safely enjoy the garden’s decking area.


Should composite decking be sloped?

Yes, composite deck boards do benefit from a slight slope during installation. It is not a set rule that composite decking must be installed with a light incline, but it does offer benefits.

A 1% gradient will not be noticeable when using the decking area, but it can help drainage. Install decking boards, so the grooves flow with the gradient to minimise the risk of standing water.


Why shouldn’t I screw directly into composite decking?

You should not screw directly into composite decking because it inhibits the board’s movement during thermal expansion. Composite decking boards can expand in the heat, and screwing them in place can cause the board to warp if it heats up.

Hidden fasteners are a great way to secure boards without screwing through them. The fastener is screwed to the joist and clips around the board, allowing expansion while holding it firmly in place.


Why should I leave gaps when laying composite decking?

Allowing expansion gaps in between composite deck boards allow the boards to expand without pushing against other boards or adjoining walls. Not having a relevant expansion gap between boards can lead to the boards warping if they have nowhere to go.

Gaps are also needed to improve drainage and ventilation. This minimises the risk of standing water on the boards. Continued exposure to moisture can also lead to mould and mildew that can cause a slip risk and stains.


Final Thoughts

It is possible to lay decking on most surfaces as long as you take the time to prepare the area properly beforehand.

Composite is a heavy material that requires suitable support to perform to its abilities and last.

If you plan to create a composite deck board area, you must adhere to the supplier installation instructions. The advice and accessories are designed specifically for the material you will be working with.

Gary is the founder and CEO of Ecoscape UK. Gary graduated from Liverpool JM University in 2007 with a 2:1 in Economics. A passion for innovation, design and sustainability, Gary has put to market numerous wpc products/systems, some of which have UK and European registered designs. Outside of work Gary enjoys spending time with his family, the great outdoors and watching Manchester United.