When you actually need it

Existing foundations have moved or are inadequate for new loads. Sometimes triggered by an extension landing on a shallow Victorian foundation, sometimes by subsidence from trees or leaks.

How it is done

Excavate in short sections beneath the existing foundation, in a sequence designed to keep the wall supported, pour mass concrete or install mini piles, then move to the next section.

What to demand

An engineer-designed sequence, a method statement, and Building Control inspections at each bay. Underpinning without those records is impossible to evidence later.