What is backfilling?
Backfilling is the process of refilling excavated soil around a foundation, wall or structure, so that the ground level connects to the building and rainwater can drain away from the construction. It is an essential step in the building process that contributes to water management and the longevity of the structure.
Why backfill?
After constructing a foundation or basement, a trench or excavation remains. This must be refilled with soil. Backfilling serves several purposes:
- Water drainage — by applying the soil with a slight slope (gradient), rainwater flows away from the foundation
- Stability — the backfilled soil provides lateral support to foundation walls
- Frost protection — sufficient soil cover protects the foundation against frost heave
- Finishing — the terrain is made level and usable again
Application
Backfilling occurs in virtually every building project:
- Foundations — after pouring a strip or pad foundation
- Basements — the space between basement wall and excavation is backfilled
- Utilities — cables and pipes are backfilled after laying
- Garden walls and fences — the base is backfilled for stability
Key considerations
- Use suitable material — preferably sand or slightly loamy sand, not topsoil directly against the foundation
- Compact in layers — apply soil in layers of 20-30 cm and compact each layer
- Ensure gradient — at least a 2% slope away from the building
- Allow for settlement — backfilled soil always settles somewhat over time
Related terms
- Foundation
- Slope
- Frost line
- Drainage
- Strip foundation
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