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Can You Put Decking Over Paving Slabs?

If you are considering installing decking in your garden, you may already have an existing surface of paving slabs and wonder if you can put your decking over the paving slabs in order to save time and money on your project. Paving slabs are common flooring materials in gardens, as they are usually cheap to install and easy to maintain. Despite this, many homeowners want to upgrade and enhance their outdoor space, as concrete paving slabs don’t add significant aesthetic value to your exterior landscape. If you want to change your outdoor flooring from paving slabs to decking, this article is for you.

Laying decking over an existing hard surface, such as paving slabs, is a simple process that can be completed without hiring a professional. We have created a simple step-by-step guide to constructing decking over paving slabs in your garden to ease the project if you are completing it yourself. Often homeowners who are looking to build decking on existing paving slabs have multiple questions about the installation process and extra necessary information such as cost or planning permission. Therefore, we have compiled some frequently asked customer questions to help guide you through the process quickly and smoothly. 

FAQs from Customers

Can you lay decking straight on top of paving?

You can lay composite decking over the top of existing paving slabs. All that is necessary is a substructure frame of joists. In fact, hard surfaces such as concrete paving are ideal surfaces to lay decking onto, as they are stable and durable materials. Laying directly onto existing paving means no requirement for wooden posts, which not only eases the process as there are fewer materials necessary to complete the project but lowers cost too. You will still have to create a substructure using composite joists or battens on top of the paving in order to support the decking to avoid any structural failure. A substructure is necessary to allow airflow and drainage, which will help to stop water from pooling on the decking surface. It is important to note when laying decking on top of paving that the existing paving surface must be in good condition, as damaged slabs can lead to the sinking of the decking on top, affecting its stability and safety. However, if you are constructing timber joists, you will need pedestals or even composite posts in order to raise the decking to prevent rotting or moisture damage. 

How do you cover old paving?

Paving slabs can come in a variety of materials. Paving slabs can be made from concrete, stone or even porcelain. If you want to cover your paving for aesthetic value or to update old paving, you can cover your paving slabs no matter the material, as long as they aren’t damaged to a point that will affect the structural stability of the decking placed on top. You can cover old paving by installing a decking material of your choice over the top of it. You can install wooden decking or composite decking over your paving slabs. 

What are the pros & cons of putting decking on paving slabs?

As with any construction project, there are pros and cons to consider prior to installation. If you are completing the project yourself, this will save labour costs from hiring a professional. However, a con of this is that it will likely take longer to complete the project if you don’t have experience in construction. Additionally, there is more chance of making any mistakes on the project if you don’t have experience with constructing decking, which can lead to material wastage and more money spent on additional materials. A benefit of building directly onto paving slabs is that there is no need to dig up your garden for posts if you are installing or flattening the surface area; this saves time in your project and requires fewer materials and tools, saving you money as well. Despite this, if your paving slabs are cracked or damaged, you will need to replace them in order to have a stable foundation for your decking boards, which will cost you time and money. 

Is it more cost-effective to put decking over paving slabs?

If you have existing paving slabs in your garden and are looking to upgrade the area to decking, it is more cost-effective to build on top of the paving slabs than ripping out the existing material and building on soft ground. The job will be quicker and, therefore, cheaper if you hire a professional to complete the job for you. Additionally, as the concrete paving acts as a solid surface for the frame to be placed on, for composite joists/battens, fewer tools and materials are required to construct the decking, which in turn will bring down the cost of the project. Pedestals will need to be purchased when using a timber frame to support your decking.

Can you lay decking on uneven slabs?

When using composite joists to lay directly on top of slabs to create your frame, you cannot lay joists on uneven slabs, as this would compromise the structural stability of the decking. This is also the case for a timber substructure, however pedestals are a great option for uneven surface.

How do you attach decking to paving slabs?

In order to put your decking on paving slabs, you will need to create a substructure of joists to make a frame for the decking to sit on securely. This is important as every decking project requires a frame in order to allow for airflow and drainage. Without this, the decking will be susceptible to rotting, warping and damage from moisture. This, in turn, will reduce the lifespan of the decking, leading to the need to repair or replace your decking boards, which is costly and time-consuming. 

A subframe provides your decking with the structural stability it needs to be able to safely hold the pressure of people, furniture and anything placed on top of it. Not only would it reduce the lifespan of your decking without one, but it would also be unsafe to utilise. 

Constructing a subframe is a simple process, requiring only joists, joist hangers, screws and a drill. You may need a saw to cut the joists to your desired size. Additionally, you may require pedestals if you are utilising a timber joist frame.

Step-by-step guide

Tools needed

Drill, Screwdriver, Mitre saw, Tape measure & Spirit level

If you are completing this project yourself, follow the instructions below in order to successfully lay your decking onto paving slabs. If you have no experience in construction or are confused at any point of installation, we recommend hiring a professional to accurately complete the job for you. Additionally, you must remember to prioritise safety first and foremost throughout the entirety of your project. Utilising protective equipment where necessary, such as protective eyewear and gloves, to prevent any injury from occurring.

Check the condition of the slabs

You will need to investigate the condition of the slabs prior to constructing a frame on top of them. You will not be able to build the substructure on damaged or broken slabs, as this can lead to sinking and structural instability of the decking on top.

Remember that you need to ensure that there is no pooling on the decking surface, as this means the existing slabs don’t have a gradient already, which allows for surface runoff. If there are drainage issues with your existing paving slabs, you will need to use pedestals to raise the decking to be able to create a slight gradient, regardless of the material used.

Choose your frame material

The installation process is different depending on the material of the frame you will be installing. If the joists you use to support your decking are composite battens or joists, you can lay the joist directly onto the slabs.

If you are using timber to create your subframe, you must use pedestals to raise the timber off the ground. It is recommended that you use 8/9 pedestals for every square metre. Please note that c16 or c24 treated timber joists are highly recommended for any ground-level decking.

The best joist and most cost-effective solution in our experience are to use composite battens, as mentioned, can be laid directly on the paving slabs.

Again, ensure that there is a slight gradient to allow for surface runoff. We recommend a gradient of 2.5%.

Building a frame

When building a composite frame, you can build your joists directly on top of the paving slabs. Your joist centre must be 300mm. Build your frame in a grid-like formation, with composite joists or battens anchored by bolt or l bracket to create a solid, stable structure.

Please note any adjoining composite joists/battens will need to be anchored or fixed together leaving a 10mm gap for expansion, using a joist cross member pre dill and screwed into place is also an advisable idea when adjoining. Please note if you are focus on structural integrity then your best option is to meet the adjoin with another frame drill and screwed with galvanised screws.

If you are constructing a timber substructure, you will need to raise the substructure in order to prevent rotting or warping from moisture. You can do this using pedestals placed on your even paving slabs and laying the joists on the pedestals, ensure you fixed the joists to the pedestals, especially when adjoining joist meet, using another frame drill and fixed into place as mentioned above, you can use a joist cross member, but this may isn’t the recommended as best practise for structural integrity.

Lay your boards

Once your frame is complete, you can begin to lay your decking on top of the joists. Start the process using starter clips, then shift over to hidden fasteners to complete the project.

Finish your project

You can finish your decking project using fascia or corner trims in order to hide any exposed edges or grooves that show.

In conclusion, yes, you can put decking over paving slabs. Eliminating the need to dig up any existing surface material. However, you will need to ensure there are no issues or damage to the decking slabs, such as drainage problems affecting the decking on top. It is also important to remember that the material of the frame you are fitting changes the installation process slightly. To construct a timber substructure, you must raise the decking for drainage purposes.

You can easily complete this process yourself by following the step-by-step guide above.

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