Underpinning: when a building needs it, and what it involves

Underpinning means working beneath a building that has to stay standing. Section width and sequence decide whether that goes well.

Foundation problems rarely arrive as a surprise. The signals usually run years ahead of anything being done about them: cracking in facades, doors and windows starting to bind, floors falling away.

When it applies

• Settlement - cracks that grow, binding doors, sloping floors
• Decayed timber pile foundations - a real risk in pre-war building stock where groundwater has dropped
• Added load - a roof addition or extra storey the foundation never knew about
• Concentrated point loads - for example after an opening, where a line load becomes two point loads

That last point is the most commonly missed. An opening gets assessed on the portal, while whether the foundation can take the new point load matters just as much.

What underpinning is

Underpinning means extending or rebuilding the existing foundation from below, so it bears deeper or spreads across a larger area. The building stays standing throughout.

That last part is the entire challenge. You're working beneath a structure that has to remain upright, and every open section is a length of foundation temporarily carrying nothing.

Section width and sequence

So the work runs in phases. A limited section is excavated, underpinned and cast. Only once that has cured does the next section open.

How wide a section may be, and in what order sections are taken, is set in advance. Too wide, or too quickly in succession, and the building settles into the excavation.

With underpinning, sequence matters more than speed. That's why we set it out beforehand and not on site.

Combining with floor replacement

If the floor has to come out anyway, the foundation is already exposed. That's the cheapest moment to deal with it. Coming back later means breaking everything open again - paying twice for the same excavation.

So we combine the two as standard wherever possible, rather than running them as separate contracts.

← Back to overview