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Driveway sub-base: depth, type and quantity

Published Reviewed 2 min read

Direct answer

The sub-base is the compacted granular layer under a driveway surface that spreads vehicle loads into the ground. GOV.UK describes about 200–250 mm of total construction for permeable front-garden drives, including about 150 mm of sub-base. These are illustrative dimensions, not a specification for every driveway. Permeable systems use open-graded material so water can pass through or be stored.

The sub-base spreads vehicle loads and can also store or pass water in a permeable design. Its specification depends on the chosen system and site.

Key takeaways

  • The sub-base spreads vehicle loads into the ground beneath.
  • GOV.UK describes 200–250 mm of total construction for permeable front-garden drives; it is not a universal depth.
  • Permeable paving requires an open-graded sub-base, such as 4/20 or Type 3.
  • The cited peg test is a rough clue, not a site design or engineering assessment.

What the sub-base does

Vehicle weight travels through the surface and has to be spread before it reaches the soil. The sub-base is the layer that does the spreading.

It also provides a stable platform so the surface above does not rut or settle unevenly.

  • Spreads load into the ground below.
  • Provides a level, stable platform for the surface.
  • Stores or passes water, depending on whether it is open-graded.

Sources for this section: GOV.UK, Guidance on the permeable surfacing of front gardens (page updated 2021-11-12; text copyright 2009; observed 2026-09-25)

Open-graded for permeable paving

A permeable surface needs a drainage path through or below it. The cited guidance specifies open-graded aggregate for that system; dense Type 1 does not provide the same void storage.

England's GOV.UK guide names 4/20 and Type 3 open-graded aggregate for permeable systems; the sub-base is compacted as in conventional construction.

  • The sub-base must have open voids and no fine material.
  • Compaction is still required, as for conventional construction.
  • The cited GOV.UK guide suggests a short hosepipe check for the finished surface; it is not a drainage-capacity or sub-base design test.

Sources for this section: GOV.UK, Guidance on the permeable surfacing of front gardens (page updated 2021-11-12; text copyright 2009; observed 2026-09-25)

Judging the ground

The GOV.UK publication describes a 50 mm square peg as a rough check; penetration depth is only a screening clue, not a project design or geotechnical assessment.

If ground is soft, variable, filled or waterlogged, seek competent advice instead of relying on the peg test.

  • The guide says easy penetration beyond 150 mm may indicate soft ground; this is a screening cue, not a 150 mm peg length or a construction-depth specification.
  • Easy penetration, made ground or variable soil: ask a competent driveway or drainage professional.
  • The guidance says clay soils may need a drainage connection; the route and discharge point are site-specific.

Sources for this section: GOV.UK, Guidance on the permeable surfacing of front gardens (page updated 2021-11-12; text copyright 2009; observed 2026-09-25)

Next steps

  1. Confirm the sub-base depth and grading before ordering material.
  2. Check the soil type if the ground is soft or clay.

Sources

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