Independent reference. UK figures verified 21 June 2026. No vendor affiliation.
Phase

New build foundations cost

Foundation type and depth turn on ground conditions and proximity to trees. Strip is the cheap, default answer on dry sand or gravel; raft is forced by soft clay or made ground; piled is forced by deep peat, heave-prone clay near mature trees, or shallow tree-protection orders. Order of magnitude: £12k strip, £18k-£28k raft, £25k-£40k+ piled for a typical 200 sqm replacement.

Oliver Wakefield-Smith · Updated 21 June 2026 · Reviewed against LABC foundations guidance, FMB House Builders Cost Guide, NHBC Standards

Strip foundations

Trench fill or traditional strip on firm ground at 1.0-1.5m depth. The cheapest option at £12,000 to £18,000 for a typical 200 sqm replacement. NHBC Chapter 4.2 sets the standard; LABC adopts the same. Works for most suburban plots away from mature trees.

Raft foundations

Reinforced slab spreading load across the whole footprint at £18,000 to £28,000. Forced by soft clay, made ground, or where deeper strip would conflict with services. Slightly faster on programme than strip; uses more concrete and rebar.

Piled foundations + ring beam

Mini-piles (typically CFA or driven) at 6-12m depth, capped with a ring beam, £25,000 to £40,000+ on a standard 200 sqm replacement. Forced by deep peat, heave-prone London Clay near oaks or willows, Tree Preservation Orders, or shallow Made Ground. The site investigation will tell you within a working day whether piling is on the table.

Ground investigation up front

Boreholes plus trial pits plus a chemical analysis: £1,200 to £3,000. Worth every penny before architect Stage 3. A foundation surprise discovered at week 8 of construction costs more in delay than the entire ground investigation budget.

Primary sources

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