This section walks you step by step through assessing your own ground so you can decide:

• which grid thickness to use
• how deep your sub-base needs to be
• whether you need reinforcement under the sub-base
• which membranes go where

By the end of this section, you should be thinking:
“I know what depth I need and exactly how my layers should be laid.”

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Step 1: Choose the correct grid thickness

For most domestic projects, this decision is straightforward.

Grid thickness (realistic guidance)

40 mm grids
This is the sensible default for:

• driveways
• parking areas
• most domestic bases

This is what I used for my driveway and what I would use again in most cases.

30 mm grids
Only really suitable for:

• paths
• very light-duty bases (small sheds, bins, walkways)

The cost saving is small, so personally I wouldn’t scrimp unless the load is genuinely light and your budget is extremely tight.

50 mm grids
Generally unnecessary for domestic use.
These are aimed at:

• commercial areas
• car parks
• repeated heavy vehicle traffic

If you’re unsure, choose 40 mm.

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Step 2: Assess your ground (no testing required)

You don’t need professional ground testing. You can learn a lot just by paying attention while excavating.

Check A: How does the soil feel?

• Very soft – wet soil easily squeezes through fingers
• Soft – moulds easily with finger pressure
• Medium – needs firm pressure to mould
• Firm / stiff – barely moulds, can only be indented

Check B: What happens when you stand on it?

• Sinks more than 50 mm → soft or very soft ground
• Sinks around 25 mm → medium ground
• Barely moves → firm ground

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Step 3: Decide your sub-base depth

Use this as a practical rule, not an engineering specification.

Medium to firm ground (most gardens and driveways)

• 100–150 mm sub-base
• Compacted in layers

This is what I used for my driveway (150 mm) and it is solid.

Soft ground

• 150–200 mm sub-base
• Extra attention to compaction
• Consider reinforcement membrane (explained in next step)

Very soft ground

• 200 mm+ sub-base
• Reinforcement strongly recommended

For light-duty bases (such as a shed base) on good ground:

• 75–100 mm can be sufficient

If you’re unsure, add depth. It’s far cheaper than fixing movement later.

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Step 4: Decide if you need reinforcement

This depends entirely on ground softness.

Medium or firm ground

• No reinforcement required

Soft or very soft ground

• Add reinforcement under the sub-base

This can be:

• a woven geotextile membrane, or
• a ground reinforcement grid

The purpose is to spread load and stop the sub-base pressing into weak soil. In most cases a decent woven geotextile membrane will do the trick.

Step 5: Normal layer order (most domestic installs)

From bottom to top:

1. Natural ground (formation level)
2. Optional woven membrane (only if ground is soft)
3. Sub-base (Type 2 suits most DIY installs)
4. Non-woven geotextile membrane
5. Screed layer
6. Gravel grids (typically 40 mm)
7. Gravel infill