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If you are installing composite decking in your garden or exterior space, you may be wondering if you can install your decking directly on top of your existing concrete paving in order to save time and money. The answer is yes, you can build composite decking on top of your concrete paving.

However, you will still need a subframe to support your decking boards and there are some important aspects you must consider before doing so. If you are considering putting composite decking over the top of your concrete paving, this is the article for you. 

Important Factors to Consider 

  • Subframe– You will still need to build a subframe for your decking boards to sit on, you cannot directly lay your decking boards on the concrete surface. Composite decking boards are created to be drilled into the joists below through their hidden fastener clipping system, which ensures a flush finish to your decking project.
    • Therefore, you will still need to install a subframe consisting of either wooden or composite joists to accurately install your composite decking. The good news is that building your subframe onto concrete paving is much easier and more straightforward in comparison to building on top of a soft surface. Unless you are raising your decking, you will not require posts to do so and can lay your joists directly on top of the concrete paving. 
  • Gradient– When installing composite decking, you will, of course, need to ensure there is a gradient to allow for surface runoff. This is imperative, no matter what material or surface you are building on top of. If you are building directly on top of your concrete paving, your concrete paving will usually already have a slight gradient. However, you must check this and ensure there is one prior to installation. 
  • Structural stability – Check that the paving is structurally sound. Before building on top of your concrete paving, you must ensure that the concrete itself is strong enough to hold the structure of the decking on top.
    • If your concrete paving is broken and damaged, then it won’t be able to withstand the weight of composite decking on top, which will lead to structural issues down the line, which can be highly dangerous. The ground needs to be stable and level to support your decking subframe safely and accurately.
    • If you are unsure about whether your existing paving is suitable, consult a professional. You will need to resurface your concrete paving if it is not structurally sound.
  • Drainage– You can use pedestals when installing directly on top of concrete paving, as the surface is flat and hard in comparison to soft surfaces such as soil. Pedestals will raise your decking off the ground to any desired height and this is also beneficial for drainage and airflow as the joists will be lifted off the ground, avoiding any moisture.
    • It is recommended to use pedestals to raise your decking to avoid water pooling, alternatively, you can also put drainage holes through the joists themselves, if structurally safe.
    • Although it is usually recommended to use composite joists for resistance and longevity when installing your subframe, you can utilise wooden joists on top of concrete paving as they are less likely to become damaged. Therefore, building on top of concrete paving can extend the lifespan of your decking. 
  • Labour cost– A benefit of building your composite decking on top of a concrete surface is that it can save you money, due to the fact that it usually doesn’t require a professional fitter. As the installation process is slightly easier, provided the existing surface is stable and level, you are more likely to be able to complete the installation process yourself. This can of course save you money on your project, as you do not have to factor in labour costs. 

Conclusion

Yes, you can build your composite decking over concrete paving. It is considered more beneficial to build on top of a hard surface in comparison to a soft surface such as soil or sand, which is permeable and more affected by moisture. If you are doing so, you must ensure there is correct drainage and that the surface is structurally sound before building on top of it.

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