Yes, composite decking can be laid over an existing concrete patio, provided the surface is stable, in good condition and suitable for supporting the new decking structure.
Using an existing concrete base can save considerable groundwork, but you’ll need to check drainage, surface condition and available height before proceeding.
In this guide, we’ll explain the benefits of laying composite decking over concrete, what to check beforehand and the considerations specific to this type of installation.
The Benefits Of Installing Composite Decking Over Concrete
Installing composite decking over an existing concrete patio can offer several advantages, provided the concrete is structurally sound and suitable for the proposed decking.
- Less groundwork: An existing concrete base may eliminate the need to construct new foundations.
- A stable supporting surface: Concrete can provide a firm base for an appropriate decking substructure.
- Fewer weeds: An intact concrete surface helps prevent weeds growing beneath the decking.
- Refresh an existing patio: Decking can transform the appearance of an old concrete area without necessarily removing it.
- Potential time savings: Reusing a suitable base can reduce preparation work compared with starting on bare ground.
However, concrete isn’t automatically free from moisture or drainage problems. The existing surface must be assessed before installing decking over it.
If you’re weighing up the advantages of decking and paving, our Composite Decking vs Patio guide explains the differences to help you decide which option is right for your outdoor space.
Things To Bear In Mind When Installing Composite Decking Over Concrete
Although it’s fairly quick and easy to install composite decking over concrete, there are several things you’ll need to be aware of before you begin. If you pay close attention to these before you start laying your decking then you shouldn’t have any issues.
Water run-off problems
When concrete patios are installed they should be on a slight slope away from your home so that moisture draws down the slope rather than towards your home.
If water is pooling in one particular area it means that the surface isn’t level. This means that you’ll need to use a concrete levelling compound to make sure that the surface is level and sloped away from your home before you lay your composite decking.
Sinking concrete
Newly laid concrete takes quite a long time to settle and in some cases, it can even take a year or more. If you install composite decking on concrete that is still settling then there’s a good chance that the decking will sink over time.
You can make a small mark on your house foundation close to the patio and a mark on the patio itself, and then use a helper and level to measure whether your patio is still settling. This process will need to be carried out over several months.
Patio stairs
If you have stairs that are attached to your patio then you will need to increase the height of the treads before you begin the composite decking installation.
This is needed to make sure that the height of each individual step remains consistent once the composite decking boards or composite decking tiles are installed.
An easier way of dealing with this issue is to lay decking over the steps. However, this will not always be possible and you will need to check the manufacturer’s instructions regarding water drainage and airflow.
Adjoining doors
If you have a door that leads onto your patio you need to make sure that installing a composite deck isn’t going to create a tripping hazard or prevent the door from opening. Remember, a new composite deck will increase the height of the patio surface by at least 25mm.
An easy way to test this is to take a piece of wood or a concrete slab that’s 3 inches tall, place it next to the door on your patio, and see if the door catches it when you open it. You should also try placing it in front of you and then walking out of the door to see if you would trip over it.
If you do identify an issue during this test it doesn’t necessarily mean that installing decking won’t be possible. However, it would probably be best to ask for a professional opinion about how to resolve the problem.
Fitting Composite Decking Over a Concrete Base
Once the concrete has been assessed and a suitable supporting structure is in place, the composite decking boards can be fitted according to the manufacturer’s instructions.
The board-fixing process is largely the same as for other supported composite decking installations. However, existing concrete steps, door thresholds and changes in height may need additional consideration.
For detailed instructions on positioning and fixing the boards, see our How to Install Composite Decking guide.
Useful Tips For Laying Composite Decking On Concrete
Pre-drilling holes
To make sure you don’t split or damage the the plastic, timber or aluminium joists you should always use a hammer drill to pre-drill holes into them before securing them with screws.
Proper gapping
Make sure to create proper gapping during the deck installation. This will allow for shrinkage, expansion and contraction, and water drainage. Using hidden fasteners is a good way of doing this.
Anchored posts
If you need to use posts to adjust the height of your composite deck then you need to ensure they’re firmly anchored to the concrete. This will help you to create a stable frame. Try using metal connectors to attach the posts to the concrete.
FAQs
How much does it cost to have a composite deck installed?
Laying composite decking materials over concrete is fairly straightforward and you can probably do it yourself. However, if you’d rather hire a professional to do it the costs will vary greatly depending on the size of the outdoor space that you want the decking to be laid on.
For a more detailed breakdown of material prices, installation costs and typical project budgets, see our guide to how much composite decking costs in the UK.
Final Thoughts
As long as you follow all the right steps and make the necessary preparations installing composite decking over concrete is fairly straightforward.
It actually has quite a lot of benefits and when compared with sand or gravel, concrete is a great surface for installing a deck.
Although the process is quite simple, if you have any concerns about things like levelling then it’s always a good idea to consult with one of our professionals before you begin laying your deck. This way, you can be sure there will be no issues further down the line.
So, check out our wide range of composite decking materials and grab your drill and screws and start laying that deck!
