How to Lay Decking on Uneven Ground: 2 Simple Methods

As landscapers we install decking on all types of ground including uneven ground. Different methods are available depending on what you mean by uneven. If you are working on a slope then cemented in support posts would be best. If you are working on generally uneven ground you can opt to level the ground or to work from support posts.

Method 1: Post-supported base

Best for: Decking on slopes or which needs elevation above 15cm.

Downsides: Can be hard to do if you are new to installing decking on uneven ground.

To build a decking base on sloped uneven ground:

• Clear the area of all grass, weeds and debris using a good quality spade.
• Dig 1ft deep post holes.
• Set the posts using post mix so that the top is at or slightly above the desired height.
• Fix joists to posts at correct level using an electric screw driver and 100mm wood screws. Cut off any excess post with a hand saw.

You are now ready to install the decking frame and decking boards on a level support structure. This method can also be used on generally lumpy and uneven ground to elevate the decking above the uneven surface. Of course you need to make sure that any edges are made safe using steps or barriers.

Method 2: Level supporting base

Best for: Low level decking.

Downsides: Can require a lot of digging and shifting materials.

Materials:

• Type 1 MOT hardcore
• Old/cheap paving slabs
• Wood for frame and legs

If you want to lay decking at ground level or slightly above but have lumpy/uneven ground this is the best method we have found to do so.

• Mark out the area then excavate to 200mm below where you want the surface of the decking to be.
• Add and compact a 50 mm layer of type 1 MOT hardcore.
• Build the decking frame. Pro tip: For quick, clean cuts use a chop saw.
• Lay out the paving slabs down the centre and along the edges of the area. These will act as solid supports to spread the weight of the decking.
• Set the decking on the slabs. Pro tip: There is a good chance that the slabs will not be even and that some parts of the decking will be too high or too low. Screw adjustable legs or use packers to get everything perfectly level.

Check out our article for laying decking directly onto soil for more options.