What is foundation underpinning?

Foundation underpinning adds support beneath an existing building to strengthen its foundation. It can extend the foundation deeper, with concrete work carried out in phases.

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By InstaBids editorial team with AI research agents. Updated 30 October 2026

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When is underpinning used?

Welsh Government guidance lists an added story as a reason for underpinning when the existing foundation is too shallow to support the changed building. “There has been a decision to add another storey to the building, either above or below ground level, and the depth of the existing foundations is inadequate to support the modified building or load (weight) of it.” Source: Welsh Government, read 2026-10-30.

What is foundation underpinning in building terminology?

New York City’s building glossary describes underpinning as a foundation below ground that supports or strengthens a building. “A solid foundation laid below ground level to support or strengthen a building.” Source: New York City Department of Buildings, read 2026-10-30.

How does underpinning work?

Welsh Government guidance describes replacing soil below the existing foundation with concrete in phases, typically working on short sections one at a time. “The soil beneath the existing foundation is excavated and is replaced with foundation material, normally concrete, in phases.” Source: Welsh Government, read 2026-10-30. “A typical method is for short sections of underpinning to be carried out one at a time.” Source: Welsh Government, read 2026-10-30.

What are the different types of underpinning?

Concrete piers, drilled piles, jacked piles and bracket piles are examples named in New York City Building Code section 1817.4.1. “If the foundation loads are to be transferred to a lower bearing level, underpinning consisting of concrete piers, drilled piles, jacked piles, bracket piles, or similar engineered systems to transfer the existing building loads below the bottom of the proposed excavation shall be installed.” Source: New York City Department of Buildings, read 2026-10-30.

What are the risks of underpinning?

Underpinning removes soil beneath existing foundations; Welsh Government guidance warns that improper work can damage or collapse the home. “If not carried out properly, this kind of work poses very real risks and could see damage to or collapse of the existing home.” Source: Welsh Government, read 2026-10-30.

Sources

Key Project Terms: Shoring, Underpinning of Foundations, and Ground Structures — New York City Department of Buildings; read 2026-10-30.
Building regulations: underpinning (Wales; technical guidance) — Welsh Government; read 2026-10-30.
2022 New York City Building Code, Chapter 18, Section 1817.4.1: Underpinning — New York City Department of Buildings; read 2026-10-30.