What is a sub-base?
A sub-base is the compacted layer of aggregate (typically MOT Type 1) laid beneath paving surfaces to distribute loads and prevent uneven settling.
The sub-base is the foundational aggregate layer installed directly on the soil beneath any paving surface. Usually made from MOT Type 1 material, a recycled crushed stone and dust, it compacts firmly to create a stable, load-bearing platform for the paving above.
Its primary role is to distribute the weight of vehicles, people, and the paving itself evenly across the ground, preventing the surface from settling unevenly or developing cracks. Without a proper sub-base, soft ground or clay-rich soil can shift seasonally, causing paving to break up or sink in patches. This is particularly important in areas with heavy rainfall or poor drainage, where ground movement is more likely.
Depth varies by use. For patios and light foot traffic, 75-100mm of compacted sub-base is typical. Driveways, which bear vehicle weight regularly, usually need 100-150mm to ensure adequate support and longevity. The thickness also depends on existing soil conditions and local ground stability. Cheltenham contractors will assess site conditions before recommending the appropriate depth for your project.
Proper compaction is critical. Loose or poorly consolidated sub-base will fail to prevent movement, undermining even high-quality paving. Local paving contractors will use mechanical compactors to achieve the required density.