What is a sub-base?
A compacted layer of crushed stone (typically MOT Type 1) laid directly on the ground beneath paving to distribute load and prevent subsidence or heave.
The sub-base is the foundation layer that sits between the soil and your finished paving surface. It consists of compacted crushed stone, most commonly MOT Type 1 material, which binds naturally as it settles. This layer does two critical jobs: it spreads the weight of the paving across a wider area of ground, and it provides drainage while preventing the soil beneath from moving or heaving due to frost or moisture changes.
In Cheltenham, where ground conditions can vary, the depth of sub-base matters significantly. A domestic driveway typically needs 100-150mm of compacted sub-base, while a patio often requires only 75-100mm since it carries lighter foot traffic rather than vehicle weight. Heavy clay soils or poorly drained ground may demand additional depth. Without proper sub-base preparation, paving will crack, settle unevenly, or develop puddles as the ground shifts over time.
Contractors preparing your site will excavate, level the ground, then lay and compact the crushed stone in layers to achieve the required density. Proper compaction is essential, which is why experienced paving contractors use mechanical plate compactors or rollers rather than hand tamping. The finished sub-base should be firm and level before any further layers or the final paving surface goes down.