Can You Lay Composite Decking Over An Existing Wooden Deck?

If you have an existing wooden deck that’s looking a bit tired and damaged you may be considering replacing it with a composite deck. This would mean ripping out all of the wooden boards and their foundations and then laying an entirely new deck from scratch.

However, it’s relatively easy to lay composite decking over an existing wooden deck. Although there are some risks to this approach there are also many benefits.

In this article, we’re going to take a look at how to lay a composite deck over existing wood decking. We’ll also closely examine the pros and cons of doing so, to get you up to speed.


Things To Consider Before You Install Composite Decking Over An Existing Wood Deck

So, we’ve established that it’s fine to install composite decking over existing wood decking. However, before you begin the installation process there are several important factors to consider.

Remember that the condition of the existing deck will directly impact the new composite deck that you lay on top of it. You’ll need to consider the amount of decay in the existing deck, how long it’s been in use and the type of wood that was used to build the existing deck.

Another important factor is the distance between joists, our composite boards are recommended to be installed at 400mm centres. Some timber deck boards have bigger spans, so you may find you will need to add extra timbers to reduce the centres to 400mm.


Wooden deck rot

If the existing wood deck is very rotten then it is unlikely that you’ll be able to lay composite decking boards over the top of it. Composite decking is very rot-resistant but the substructure needed to support it may start to rot when exposed to a rotting wooden deck over time.

If the existing deck is rotting badly then this will lead to moisture being trapped underneath the new composite deck which will lead to further rotting.


Types of wood

It’s also beneficial for you to make sure that you check the type of wood that was used to construct the existing wood decking. Woods such as cedar, mahogany, and redwood are the most rot-resistant types.

This means that building a composite deck over decks made from these woods shouldn’t compromise the longevity of the composite decking.


Existing wood decking replacement

If the wooden deck is too rotten and decayed then you will have to consider replacing it with a new composite deck rather than laying one on top of it.

An easy way to check the level of rot and decay in your wooden deck is to push into several wooden decking boards with a screwdriver. If there are many areas where the wood is soft and pushes in easily, then it will most likely need to be replaced.

If you lay a composite deck over a very rotten wood deck then the composite deck boards and the substructure may also start to rot. This could lead to the composite decking boards collapsing at some stage.


How To Install Composite Decking Over An Existing Wood Deck

Installing composite decking over existing wooden decks is fairly straightforward. However, you need to take the time to make sure that you do it correctly to avoid any issues further down the line.

Before you begin, make sure that your wooden deck is clear of any obstructions such as garden furniture. You will also need to remove your deck railings balusters before you get started.

Then, follow the steps below to safely and effectively install composite decking over the wood deck.


Step 1

Firstly, use a pry bar and remove the boards from your old wooden deck. You can then take some of these wood deck boards and use them to create a temporary block line.

Once you’ve done this, carry out a thorough inspection of the wood deck framing and check for rot. If you notice significant rotting in any areas of the frame then this will need to be repaired or replaced before you go any further.

If there are any sections of the framing which are weak or wobbly then support them with additional framing before you continue.


Step 2

The next step is to use a high-quality wood preservative to treat any of the cut ends on your wood deck frame. This is to prevent them from rotting in the future once they’ve been covered by the composite decking.

Then, use joist protection tape to cover up any holes from screws or nails in the pre-existing wood decking. This is done to stop water from gathering in the holes which would lead to the formation of rot and mould.


Step 3

Now, the composite boards need to be cut to the right length allowing for the correct amount of gapping at the ends. Use a 3mm drill to pre-drill holes into the composite boards to prevent them from splitting later on. Then, start to secure the boards with 25mm, 8-gauge deck screws.

If you’re using fasteners instead then there is no need to pre-drill the composite boards. Ecoscape supply T-clips, locking clips and start finish clips. We only recommend screwing through the board when absolutely necessary, usually on the last deck board which has been cut down where a hidden fastener cannot be used.

Start installing the composite deck boards from the outside of the deck and work your way towards the building. You should use a jigsaw to cut around any railing posts as you go.


Step 4

Next, cut the middle boards to a suitable length. Start installing them by moving them out from the breaker board towards the perimeter boards. Remember to work your way in from the outside of the deck towards the building.

As you’re installing the composite decking, make sure you’re using spacers so that the right amount of space is left between the boards. Ecoscape T-clips provide a 5mm gap between boards.

This is crucial as the boards will need enough space to expand in heat and contract in the cold without becoming damaged. The right amount of spacing also allows for proper water drainage, and for debris to fall through.


Step 5

Now that you’ve installed your new composite decking over your old wooden decking there are just a couple of things left to do.

First, have a final inspection of the composite decking to check that all screws, fasteners or nails are fully secured and intact. Then, check each of the composite boards to make sure that they’re sturdy and that they don’t bend when weight is applied to them.

If you’re planning to seal your composite decking then apply this now and give it the right amount of time to dry. Composite decking doesn’t need to be sealed but doing so can give it extra protection and durability.

Once this is all done, you can now re-install the railing balusters and place your garden furniture onto your new composite deck.


Pros & Cons Of Installing Composite Decking Over An Existing Wood Deck


  • It’s easier and less time-consuming than fully replacing your old wooden deck.
  • Installing new composite decking over wood decking is a good way to give a fresh look to your outside area.
  • Composite decking requires far less maintenance than wood. It doesn’t need to be sealed, treated, or stained, and it only needs to be cleaned every now and again.
  • Composite decking is more durable than wood. This means you will save money in the long term as it doesn’t need to be repaired in the same way that wood does.
  • Composite boards are easier to install than wooden ones and are less likely to split whilst being installed.
  • Composite decking has a long lifespan and doesn’t need to be replaced as often as wood.
  • Composite is a much more environmentally-friendly material than wood. It’s made from recycled wood and plastics meaning that no new trees have to be felled to make it.
  • Composite boards come in a wide range of colours including charcoal, ash, and silver birch. As they’re already coloured, you don’t need to spend time and money painting them.



  • If you don’t properly inspect your old wooden deck and its foundations for rot then it could affect your new composite decking.
  • The upfront cost of composite decking is higher than it is for wood. However, this is offset by the money you will save over time.
  • If you install composite decking over wood decking it means you will need to clean your deck more often than if it was just a composite deck. This is because debris and fluid may become trapped between the two layers of decking.



Is composite heavier than wood?

As it’s made with a mixture of wood fibres and plastic polymers, composite does tend to be heavier than wood. On average, composite decking is around 25% heavier than wood decking.


Is it better to use screws or nails to secure composite decking?

It is not recommended to use screws through composite decking o any composite material. The reason being, is this prevents expansion and contraction of the product which can lead to buckling or warping. Ecoscape recommends using hidden t-clips every 400mm, the t-clip allows expansion and contraction. If you do need to screw through composite deck boards, then make sure you pre-drill and counter sink, this will help with the expansion and contraction as well as provide a neat finish.


Does composite decking need to be cut with a special saw blade?

Cutting composite decking is just as easy as cutting wood as long as you use a sharp, flexible blade. You can use a regular jigsaw to cut composite but check the manufacturer’s instructions to see which blade you should use. We find the best blades are multipurpose aluminium blades.


What’s the best way of hiding screw holes in composite boards?

If you want to hide the screw holes in your composite decking there are a few easy ways to do it. One way is to make a mixture of silicone caulk and composite board shavings and then fill the holes using a putty knife.

You can avoid having screw holes altogether by securing the boards with hidden fasteners.

Pre-drilling and screwing with our smart bit will provide a professional finish on your composite deck.


Final Thoughts

Laying composite decking over existing wood decking is fairly simple and has several benefits. It’s less time-consuming than fully replacing a wooden deck and is an easy way to revitalise the look of your outdoor space.

Remember, you must check the existing wood deck and its foundations for any rot before you begin. As long as you do this, then laying a composite deck over an existing wood deck should be plain sailing.

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.