Building Regulations: Walls Below Ground Level (Substructure)

When you're building an extension, the section of the wall that extends below ground level is known as the substructure. These essential, hidden walls are responsible for providing robust support for the visible walls above ground, which we refer to as the superstructure.

The extent of substructure required for your project will vary. It depends directly on the type of foundation you are implementing, specifically whether it's a deep-fill or a shallow-fill design.

Your substructure has one crucial purpose: to adequately support the superstructure above it. Therefore, the materials you select for this underground work – such as bricks, blocks, and mortar – must be highly effective and durable. Importantly, they also need to be resilient against the specific conditions found in the ground, meaning they must be resistant to both frost and any sulphates present in the soil.