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Can I Put Composite Decking Over An Existing Wood Deck?

Creaking, wobbling, and rotting floors are clear signs that you should replace your wood decking. Not only does it look bad, but it’s also a safety hazard. The sooner you replace your rotting decking, the better.

Since wooden decks have a limited lifespan, you may want to use something a little more durable. In this case, composite decking is perfect for the job. The question is, can you put composite decking over existing wooden decking to save time and money?

Installing composite decking on top of old timber boards?

By installing composite decking directly on top of your old timber decking boards you will save time and money as you do not have to pull up the old decking boards but we strongly advise against this.

Composite decking requires adequate ventilation beneath the boards to help prevent buildup of moisture and mildew. By installing composite decking boards directly onto your old timber decking, you won’t allow for any room for air circulation.

Proper ventilation is essential for preventing the growth of mould. Without sufficient airflow, it is only a matter of time before mould starts to grow as a result of moisture being trapped between the decking boards and the underlying timber structure.

Your boards will also have a current gradient and laying boards onto of the previous or old decking if not aligned correctly can cause water pooling and deformation of the new decking boards. For all the above reason this is why we highly advise against it.

Using your old timber frame for your new composite decking?

There are some cases where homeowners can use their old, existing timber decking subframe with their new composite decking boards. This method would consist of pulling up the old timber decking and replacing it with the new composite decking. A issue raised by fitters is that pre existing drill holes from your previous installation can increase the time and make it challenging to secure into place.

Having the option to do this is dependent on multiple factors, such as:

Structural integrity of the sub-frame: You must ensure that all joists are in good condition. Checking that there is no rot, decay, or damage will ensure that your decking area remains safe and structurally sound. For those who have issues with their sub-frame, we strongly recommend that you replace your joists and posts to ensure you have a long-lasting and durable decking area.

Joist Spacing: You must pay attention to the installation requirements for your composite decking boards. Most composite decking suppliers offer warranties to cover any structural issues, such as bending or warping. To remain compliant with the warranties, you must ensure you have the correct spacing for the sub-frame. For example, if your current joist centres are 500mm and the requirement for your composite decking is 300mm, you may want to think twice about using your current subframe.

Gradient Check: Your existing subframe will or should have a current gradient, this will need to be checked and possibly adjusted to allow a 2.5% or 1/40 gradient running away from the property for your new composite decking to be installed.


To create a more durable and aesthetically pleasing decking area, the decision to replace ageing timber with composite decking is very logical.

Recognising the safety issues caused by deteriorating wood, many people consider the longevity that comes with composite decking. While there is a temptation to overlay composite boards onto existing timber boards, you should always avoid this.

However, for those who are contemplating the reuse of their existing timber subframe for their composite decking, there are numerous factors to consider, such as the structural integrity of the subframe, gradient/drainage and the joist spacing.

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