Can You Lay Composite Decking Over An Existing Wooden Deck?

Is your wooden decking in need of a modern refurb? A frequent query we often get asked is whether or not you can install composite decking directly onto an existing timber decking area.

The short answer is no. But to understand why, you’ll have to let us explain the hazards of going down that route and onboard our tips on how to combat the effects of moisture build-up on your deck. We’ll also take a look at the options you have when installing our composite decking directly onto a pre-existing timber subframe.

Honestly, this is all in all just a bad idea. Composite decking exists as a long-lasting, eco-friendly counterpart to traditional timber decking, and to combine the two is to quickly create an unstable mixture that’s bound to spell trouble for everyone involved. A nightmare for you and your installer alike, covering old decking with composite decking won’t achieve anything close to the level of quality promised by composite decking on its own. In fact, our composite boards have been specifically designed to fit onto a proper joist network to allow for optimal drainage and airflow.

By installing composite decking boards directly onto timber decking, you’d be leaving very little allowance for either, which will ultimately end in your composite deck sitting in water. And what happens then? Well, your boards will end up damaged, your warranty will be void, and you’ll be left with a mess of decking far worse than what you started with.

Not only this, but the aged timber decking underneath your new composite decking will already be prone to rotting. So, you can certainly expect that slapping some composite on top will only speed up the degradation process. To avoid this entirely, we suggest opting for the sensible option – installing our composite deck boards directly onto a joist subframe network that’s designed to work in harmony with them.

We don’t advise against this option, but there are certain things that we highly recommend when deciding on this option.

Tip #1 – Ensure that your joist spacings sit at the recommend centres of 250-350mm. Many timber decking projects have slightly wider centres that usually sit at around 500mm, so this may require reinforced timber joists. While composite deck boards are extremely hardwearing, particularly in heavy footfall areas, they require a little more support beneath them compared to ridged timber deck boards. This is due to the flexibility that composite decking’s recycled plastic introduces into the mix. When paired with wood fibres, our boards become a little more flexible than traditional timber. But trust us, adding in extra support is definitely worth it.

Tip #2 – Incorporate a drainage slope to your decking subframe where possible. This is all dependent on how well the decking subframe was built in the first place. When water sits on timber joists, problems (such as rotting and warping) start to arise. We recommend incorporating a decline rate of approximately 1:100 to your framework to combat this. By doing so, you’re giving your deck the chance to dispose of any standing water and reduce pooling beneath the framework – integral parts of keeping your composite decking protected and healthy.

Tip #3 – Always use NeoTimber® joist tape when planning a composite decking installation on top of a timber subframe. While we generally recommend opting for composite joists or plastic lumber subframes over timber subframes, we understand that sometimes it’s budget-friendly to lay composite decking onto your pre-existing or newly laid timber subframe. Joist tape will protect your timber joists and provide you with the reassurance that you have waterproof seal on the surface of your joists. Without joist tape, your timber subframe will eventually face significant weathering and rot

Tip #4 – Ensure the entire structure is equal parts stable and safe. Think twice about installing long-life composite decking boards onto failing subframes. Unfortunately, we’ve seen this happen more times than we’d like. Customers have installed our composite decking onto an aged subframe, only to find themselves ripping their deck boards up to change their subframe not long after installation. It’s far better to take care of the issues beforehand, no matter how eager for some new decking you are. If you rush it, you could end up with more problems than you started with.

Looking for more installation help? Check out our installation guide to help with the laying of your composite decking.