How to Lay Decking on Soil- Step-by-Step for a Solid, Lasting Base

Can You Lay Decking on Soil?

Yes, you can lay decking directly on soil — but it must be done properly to avoid issues with movement, moisture, and decay. Soil can shift, expand, or become unstable when wet, so the key to success is creating a level, well-drained base and using the correct support structure to keep the decking frame stable over time. When installed carefully, ground-level decking on soil can be a low-cost, practical option for garden seating areas, paths, or small terraces.

Preparing the Ground

Start by marking out the area where your decking will go. Remove all vegetation, including grass, weeds, and roots, and dig down to remove the top layer of soil — ideally to a depth of 100 to 150 millimetres. This creates space for a sub-base that improves stability and drainage.

Level the area and compact the soil firmly using a hand tamper or vibrating plate compactor. If the ground is uneven or sloped, take the time to level it or create slight gradients to prevent water pooling. Once the soil is compacted, add a weed control membrane to prevent growth beneath the decking and improve air circulation.

Adding a Sub-Base for Support

To improve stability and drainage, spread a layer of hardcore or MOT Type 1 aggregate over the compacted soil, typically around 50–75mm deep. Compact this layer until it’s firm and level. This prevents the soil beneath the decking from shifting and helps drain water away from the timber.

For extra support, you can lay concrete paving slabs or blocks on top of the sub-base to act as footings for the decking frame. These distribute weight more evenly and reduce direct contact between wood and soil, helping to prevent rot and prolong the life of the structure.

Building the Decking Frame

Use pressure-treated timber joists to build a sturdy, rectangular frame for your decking. The frame should sit above the sub-base, either resting directly on concrete blocks or supported by adjustable decking risers or short posts driven into the ground. Ensure the frame is level using a spirit level and adjust as needed.

The joists should be spaced appropriately for the decking boards you're using — typically 400mm to 600mm apart. This spacing provides strong, even support and prevents sagging or flexing over time. Add noggins (short bracing sections) between joists for extra stability, especially on larger decks.

Installing Decking Boards

Once the frame is level and secure, lay your decking boards across the joists at right angles. Use galvanised or stainless steel screws to fix the boards in place, leaving a small expansion gap between each one to allow for natural movement with changes in moisture and temperature.

Make sure your boards have a slight fall (1:100 slope is enough) away from the house or central point to encourage water runoff and prevent pooling. This extends the life of the boards and helps keep the surface safe and slip-resistant.

Finishing and Maintenance Considerations

After installation, seal the decking with a protective wood oil or stain, particularly if it’s in a high-moisture or shaded area. This guards against weather damage, rot, and discolouration. If you're using softwood boards, regular maintenance will be required to keep the surface in good condition.

Keep the area under the decking clear of debris and ensure air can circulate freely to prevent mould or moisture build-up. Check for signs of movement or settling over time and adjust or pack under supports as needed.

Avoid Direct Timber-to-Soil Contact

Even pressure-treated timber is vulnerable over time if it sits directly on damp soil. To reduce the risk of rot, always lift the timber slightly off the ground. This can be done with paving slabs, concrete blocks, or adjustable decking feet. Raising the frame, even by just a few centimetres, improves airflow and reduces moisture absorption, which significantly extends the life of the timber structure.

This is particularly important in shady or north-facing gardens, where the ground stays damp longer.

Ensure Proper Drainage Under the Deck

Decking laid on soil needs free-draining ground underneath. If the area tends to hold water, you can dig shallow trenches under the deck and fill them with gravel to act as soakaways. This prevents water from pooling beneath the timber and keeps the ground dry.

You can also rake a gentle slope away from the centre or from the house to encourage runoff. Drainage is especially important in heavy clay soils, where water tends to sit close to the surface.

Use Joist Hangers or Raised Connectors for Better Strength

For added support and to reduce sagging, use joist hangers or corner brackets to fix joists together cleanly and securely. This helps prevent structural movement over time, particularly if the soil shifts slightly during wet and dry periods.

You can also buy plastic or composite decking risers, which are rot-proof and adjustable. These are ideal for areas where the ground is uneven or if you want to futureproof the deck for settling.

Consider Ventilation

Ventilation beneath your deck is vital. A low deck with no air movement is more likely to attract mould, algae, and rot. Always leave a small gap (around 50–75mm) between the frame and any adjoining walls or structures to let air flow freely underneath.

For decks that are close to the ground, airflow can be improved by leaving small vertical gaps between the decking boards and not sealing off the sides completely.

Final Word

Laying decking on soil is entirely possible — and often more affordable — when done with care and the right groundwork. With proper levelling, drainage, and support, you can build a safe, attractive, and long-lasting deck without the need for deep foundations or concrete posts. Preparation is everything: a solid base and moisture-resistant structure are what keep your decking strong and stable for years to come.