What is a sub-base?
A compacted layer of aggregate material laid beneath paving surfaces to provide load-bearing support and drainage, typically using materials like MOT Type 1.
The sub-base is the foundational aggregate layer positioned directly above the prepared ground (subgrade) and below the finished paving surface. It performs two critical functions: distributing the weight of vehicles, foot traffic, or weather loads evenly across the ground below, and allowing water to drain away from the paving structure.
Common materials used for sub-base include MOT Type 1 (recycled crushed concrete and asphalt) and crushed stone, compacted in layers to achieve the required density. The material binds together when compressed, creating a stable platform that prevents settlement and cracking of the surface layer above.
Depth requirements differ depending on the application. A domestic driveway typically needs 100-150mm of compacted sub-base, while a patio used only for foot traffic may require just 50-100mm. Heavy-use areas or poor ground conditions demand greater depth. Paving contractors in Cheltenham assess ground conditions and load expectations to specify the correct thickness for each project.
Without an adequate sub-base, paving surfaces are prone to rutting, cracking, and premature failure as the ground shifts and settles unevenly beneath them.