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Construction method · Guide

Underpinning existing foundations

Transfer an existing building's load to new or improved support while preserving stability throughout the work.

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Conceptual section through one new support below an existing footing. This is not a bay layout or an excavation sequence.

What it does

An existing foundation may need a different load path because of ground movement, changed loading or adjacent work.

Investigate the cause, design the temporary and permanent support together, and control how load reaches the new foundation.

When it fits

  • Investigation establishes a need to alter or supplement existing support.
  • The chosen method is compatible with the structure, ground, access and neighboring property.

The trade-offs

  • Excavating near a loaded foundation can undermine its existing support.
  • Monitoring, temporary works and staged load transfer are central to the method.

Context. Existing buildings. Underpinning is a project-specific intervention; not every crack or movement requires it.

From idea to assembly

  1. Establish the cause

    Survey the building and investigate ground, water, utilities, loading and the history of movement.

  2. Design every stage

    Resolve temporary support, the permanent foundation, load transfer and monitoring before work begins.

  3. Control the transfer

    Follow the engineered sequence and its hold points; verify the new support before removing temporary measures.

The junctions that matter

Old footing to new support
A designed bearing or connection must transfer load across the interface.
New support to ground
Investigate the receiving stratum and the settlement behavior of the complete arrangement.

What can go wrong

  • The visible crack is treated without establishing its cause.
  • Excavation removes support beyond the designed stage.
  • The new foundation is present but the intended load-transfer interface is ineffective.

Try it on a building

An altered masonry building. Compare the effect of added loads with evidence of ongoing ground movement. The two situations can call for different investigations and interventions.

What this guide covers. No bay lengths, dig depths or installation sequence are prescribed here. These depend on the investigation and temporary-works design.

Connected ideas

Sources & further reading

  1. Underpinning: Good practice guidance ↗

    Temporary Works Forum and ASUC · TWf2023:02, June 2023

    Feasibility, investigation, design, load transfer and monitoring

    Feasibility, investigation, temporary support and load transfer; UK practice.

  2. Structural stability during alteration, demolition and dismantling ↗

    UK Health and Safety Executive · Online construction guidance

    Survey, structural assessment and temporary supports during alteration

    Survey, assessment and design of temporary supports during alteration; UK practice.

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