How To Lay Decking On Uneven Ground

How to lay decking on uneven ground-guide

If you’ve been dreaming of creating a beautiful outdoor space where you can entertain guests, relax with a book, or just enjoy a cup of coffee, then building a deck is the perfect solution. But what do you do when your backyard is not flat and even?

One of the most common mistakes people make when laying decking on uneven ground is not taking the time to level the surface. If the ground is not level, your deck will not be level either, which can cause all sorts of problems down the line.

For example, if the deck is not level, water may collect in certain areas, which can cause damage to the deck boards and the structure underneath. Also, an uneven deck can be a safety hazard, especially if it’s high off the ground.

Uneven ground can make deck building seem like a complicated task. However, with the right tools, a bit of planning, and professional assistance, you can create a level and sturdy deck that will stand the test of time. In this post, I’ll walk you through some tips and tricks to help you build a deck on uneven terrain.

The Best Ways To Lay Decking On Uneven Ground

Many households want to build a beautiful deck in their backyard but face the challenge of uneven ground. The bright side? There are several ways to overcome this obstacle and create a sturdy and level deck. You can always reach out to reputable decking installation services in London to get the best advice.

The approach you choose will depend on various factors, such as the degree of elevation of the ground, the materials you plan to use, and the type of deck you want to build. Let’s take a look at two popular ways of laying a deck on uneven ground: 


Building a decking on uneven ground

Use Concrete Support Posts

Building a deck is a great way to upgrade your garden. If you’re planning to build a deck attached to your house, support posts could be an excellent option to consider. They work best for areas where the slope is directed away from the building. Here’s a step-by-step guide on how to build support posts for your decking.

Step 1

The first thing you need to do is prepare the installation area. Remove any weeds, grass, and vegetation. Use a rake or shovel to level the area and remove any debris. For best results, use a whacker machine to compact and flatten the area. This ensures that the ground is stable and even, which is crucial for the support posts to work effectively.

Step 2

The next step is to dig the post holes, ensuring a depth of at least 30 cm (one foot) below solid ground. Use a post-hole digger or a shovel to dig the holes. You can also use a power auger for larger holes or to save time. Remember to keep the diameter of the holes consistent and follow building regulations for the appropriate depth.

Step 3

Choose a support post system. Pouring concrete directly into the hole and attaching concrete fasteners to the concrete is the preferred choice, especially for steeper slopes. This method ensures a sturdy base for the posts and prevents them from shifting or settling. 

Alternatively, layer the base of the hole with gravel, place the wood post into the hole and pour concrete mix to hold it in place. This method is suitable for gentler slopes and provides adequate support for the posts.

Step 4

Run and level a string line across the wood posts to determine where to attach the subframe parts. This ensures that the subframe is level and square, which is crucial for the overall stability and safety of the deck. 

Use a spirit level to check the levelness of the string line and adjust the posts if necessary. Install the beams and the joists, following local building standards for screws and wood thickness. Use galvanized or stainless-steel screws to prevent rust and ensure durability.

Step 5

Once the subframe is set, lay the decking boards. Use a spacer between each board to ensure the consistent spacing and adequate ventilation. Install railings for safety and to comply with local building standards if necessary.

You can also add a skirting board or fascia to cover the subframe and create a finished look for the deck. Lastly, apply a deck sealer or stain to protect the wood from moisture and UV damage.

This is how you can build support posts for your deck and enjoy a sturdy and level space for outdoor entertainment. Remember to check your local building regulations and obtain the necessary permits before starting your project.

Check out our blog post for everything else you need to know about the decking!

Use Concrete Slabs

Laying decking on uneven ground using concrete slabs can be a great option for low-level floating decks on generally level ground with a slight slope. Here are some more valuable details to consider for each step:

Step 1

Before starting the installation process, mark out the area you want to use for the deck. You can do this with some wooden stakes and string, or you can spray paint on the grass or soil. 

After marking the area, dig down at least 20 cm deep, making sure to remove any grass or weed in the process. Then, use a whacker machine to compact the whole excavation area. This step is crucial for ensuring a stable base for your deck.

Step 2

After preparing the excavation area, you can now cover it with landscaping fabric. This fabric helps prevent weed growth and allows for better drainage. Once you’ve covered the area, layer it with at least 50 cm of MOT Type 1 sub-base or a mixture of fine and coarse gravel. The layer will also help with drainage and provide a stable base for the concrete slabs.

Step 3

Place the concrete slabs on the installation area and ensure they are level. You can use a spirit level to make sure they are balanced. If they’re not, you can add or remove gravel until the slabs are level. Make sure to place pieces of wood on the slabs to protect them from damage while you’re working.

Step 4

Now it’s time to build the subframe of the deck. Start by constructing the beams and joists, which will support the decking boards. Make sure to place the frame over the concrete slabs and use a spirit level to check if it’s level. If it’s not, you can adjust the height of the frame by adding or removing gravel or by making adjustments to the height of the slabs.

Step 5

With the subframe in place and level, you can now lay the decking boards. Since the decking boards are close to the ground, it’s a good idea to choose high-resistant materials. Softwoods like Cedar and Redwood are good choices, and many hardwoods work well for ground-level decks.

You can also consider using non-wood alternatives, such as composite decking materials, which are durable and require less maintenance than wood.

Related: Does a deck increase the value of your home?


Decking boards on uneven ground

Final Thoughts

Laying decking on uneven ground is a daunting task, especially when you don’t have the tools and experience you need to lay decking.  To make things easier, level the ground as much as possible using a mix of excavation and grading techniques. Adding a layer of gravel or sand can also help create a more stable foundation.

Taking the time to properly prepare the ground and use quality materials will help ensure a long-lasting and sturdy deck on uneven ground.

Get inspired with some of our modern composite decking ideas.

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