Underpinning Cost UK: £1,800-£3,500/m Pricing Guide 2024

Quick Answer: UK underpinning prices at £1,800-£3,500 per linear metre of wall for traditional mass concrete underpinning (1m sections, "hit-and-miss" sequence) to a typical 1.5-2m depth. Specialist resin or piled underpinning runs £2,500-£6,000/linear m. Insurance-driven subsidence underpinning is typically priced by a specialist contractor with public liability of £5m+ and a 10-year guarantee, not a general builder.

Summary

Underpinning is a high-risk specialist activity. Failures kill people: bricklayers crushed in collapsed excavations, neighbours' walls subsiding, basements flooding. The Health and Safety Executive treats underpinning as notifiable construction work, and CDM 2015 requires a structural engineer's design and a written method statement before any pin is dug. General builders should not quote underpinning without specialist experience and appropriate insurance.

Pricing is dominated by three things: depth of the new foundation, length of wall to be underpinned, and access. A semi-detached house with a long elevation to a clear back garden underpins for £1,800-£2,500/m. The same house with a side wall against a neighbour's house, no garden access and a Victorian sewer running parallel to the wall underpins for £3,500-£5,000/m. The technique is the same; the logistics are very different.

This guide covers traditional mass concrete underpinning (still the dominant method for domestic work), and gives a brief overview of resin injection and piled solutions. It does not cover full-dig basement formation, which is a different specialism with much higher prices — see basement conversion pricing guide.

Key Facts

• Method choice depends on cause — subsidence (clay shrinkage, tree roots, leaking drains) usually addressed by mass concrete or resin; heave or settlement of compressible soil may need piles
• Typical depth — 1.5-2m for mass concrete; deeper engineered solutions for piled
• Bay sequence — "hit-and-miss" 1m bays in a 1-3-5-2-4 sequence; never excavate adjacent bays together
• Bay length — typically 1m (1.0-1.2m max for clay soils, 0.9m for granular)
• Concrete grade — minimum C20/25 to BS 8500; some engineers specify C25/30 with reinforcement
• Dry-pack to underside of existing footing — semi-dry concrete or sand-cement mortar, rammed home 24 hours after pour
• Curing time — 7 days minimum before excavating adjacent bays for mass concrete; 14-day minimum if heavily loaded
• Ground investigation — trial pit (£300-£600) or borehole (£800-£2,500) usually required by engineer
• Structural engineer's design — £900-£2,500 for typical domestic underpinning scheme
• Building Control — full plans application; multiple inspections per bay
• Party Wall Act 1996 — almost always engages Section 1, 2 or 6 (typically all three); awards required
• CDM 2015 notifiable — usually exceeds notification threshold (30+ working days, or 500+ person days, with 20+ workers); F10 notification required
• Specialist labour day rate — £280-£400/day for an experienced underpinning operative
• Builder/groundworker day rate — £200-£300/day for non-specialist supporting labour
• Skip hire and muck-away — significant; clay spoil is 1.5-1.8 tonnes/m³ and bulks 25-30% on excavation
• Drainage works — most underpinning sites discover broken or leaking drains as a cause; £800-£3,500 for diversions or lining
• Insurance-driven works — subsidence claim under buildings insurance pays specialist contractor with CSRT or ISSE accreditation; warranty 10 years
• VAT — standard 20% rated for repairs; reduced 5% rate may apply if part of an "approved alteration" under VAT Act 1994 Schedule 7A — confirm with accountant
• Warranty — 10-year structural guarantee typical from specialist contractors; general builders rarely offer this

Quick Reference Table

Detailed Guidance

When Underpinning Is Actually Needed

Most domestic "subsidence" diagnosed by an insurer turns out to require underpinning in less than 30% of cases. The more common outcomes are:

• Drain repair only — leaking drain washed soil away; fix the drain, monitor for 12-18 months, no underpinning needed
• Tree root removal — root barrier or removal eliminates clay shrinkage; monitor for heave
• Minor monitoring — cracks below 5mm wide stable over a season; cosmetic repair only

Builders should never quote underpinning on the basis of cracks alone. A monitoring period of 6-18 months with crack monitors (Avongard tell-tales £8-£15 each, professional digital monitoring £400-£800 per period) is normal practice before any structural intervention.

When underpinning IS needed:

• Progressive cracks ≥10mm wide, accelerating, with structural distortion
• Sloping floors with measured fall >1:200
• Doors and windows that have failed to close over a single season
• Engineer's diagnosis of inadequate existing foundation depth (often <450mm in Victorian terraces)

The Traditional Mass Concrete Method

Sequence per bay:

1. Mark out 1m bays in a 1-3-5-2-4 sequence (never two adjacent bays open at once).
2. Excavate bay 1 by hand. Hand-dig only is normal in the close to a wall; mini-excavators are too risky.
3. Trim sides square; shore with timber or steel sheets if depth >1.2m or soil is loose.
4. Pour concrete to within 50-75mm of the underside of the existing footing. Allow 24 hours minimum for the lift to gain set.
5. Dry-pack the gap with semi-dry concrete or sand-cement mortar, hammered tight with a ramming bar. This step transfers load — done poorly, the underpinning does nothing.
6. Backfill bay; reinstate ground.
7. Wait 7 days minimum before excavating bay 3, then 2, then 4, etc.

Time per bay: 1-2 days for the dig and pour. With 1-week cure between adjacent bays, a 5-bay (5m) length of wall takes 4-6 weeks elapsed.

Labour per bay: 2-person team, 1.5-2.5 days. Plus engineer's site visit and Building Control inspection at each bay (some inspectors visit every bay, some sample).

Resin / Geopolymer Underpinning

Specialist contractors (e.g. Geobear, URETEK, Mainmark) inject expanding polymer resin at depth around the existing foundation. The resin expands, compacts the soil and raises the foundation slightly. Best used for:

• Minor settlement (5-30mm)
• Granular soils or made-ground
• Where excavation is impossible (close to drains, restricted access)
• Rapid response (most jobs complete in 1-3 days)

Cost: £2,500-£5,000/linear m, but priced as a project rather than per metre. Typical small house: £15,000-£40,000.

Not suitable for: clay heave, deep settlement, or where the existing foundation is itself structurally inadequate.

Mini-Piling

For deeper or heavier requirements, contractors install mini-piles (typically 150-300mm diameter, 3-15m deep) at intervals along the wall, then form a reinforced concrete needle or beam linking the piles to support the existing wall. Used where:

• Made-ground or fill below the existing foundation
• Granular soils with no clay layer to bear on
• Heavy loads (commercial, multi-storey)
• Restricted headroom or access for traditional excavation

Cost: £3,500-£6,500/linear m. Specialist plant required (small mini-piling rigs cost £180-£300/day to hire, plus operator).

Pricing Walkthrough — Typical Domestic Job

A semi-detached Victorian house with 6m of front wall showing progressive subsidence cracks. Engineer diagnoses tree-root-induced clay shrinkage; tree consented for removal but underpinning required regardless. 1.8m deep mass concrete in 1m bays.

This is £5,360/m all-in. Quoted as "underpinning at £1,800/m" the customer would expect £10,800 — the gap is preliminaries, party wall, drainage, reinstatement and margin. Always price the whole job, not just the structural element.

Insurance Claims — A Different Market

Where the cause is subsidence triggering a buildings insurance claim, the insurer appoints a specialist underpinning contractor with CSRT (Certificated Surveyor in Remedial Treatment) accreditation, ISSE membership and £5m+ public liability. The customer pays only the excess (typically £1,000). General builders cannot compete in this market — the warranty alone (10 years) requires specialist insurance backing.

When a customer approaches you about subsidence, the correct response is:

1. Check whether they have buildings insurance covering subsidence (almost all UK policies do)
2. Tell them to phone the insurer to report a claim
3. Insurer appoints engineer at no cost
4. Specialist contractor priced by insurer, customer pays excess only

Builders attempting to price underpinning outside the insurance pathway often find themselves at the wrong end of a £40,000 dispute when the work fails or another part of the house subsequently moves.

Frequently Asked Questions

Is underpinning always the answer to cracks?

No. Most cracks in residential property are caused by minor thermal movement, drying shrinkage of plaster, lintel deflection, or differential settlement of additions to the original house. A 6-18 month monitoring period with engineer review is standard before any intervention. Cracks ≤5mm wide that don't widen over a season usually need only cosmetic repair.

Will my underpinning be covered by building insurance?

Yes, for subsidence claims caused by ground movement (clay shrinkage, leaking drains, tree roots). The standard excess on a subsidence claim is £1,000-£2,500. The insurer manages the works including underpinning if needed and provides the 10-year warranty.

Can I underpin myself or with a general builder?

Legally yes, but it is rarely advisable. Underpinning is CDM 2015 notifiable on most domestic jobs (durations exceed thresholds). Building Control will require an engineer's design and inspections. Insurance for general builders typically excludes specialist excavation work; check your policy. If a wall moves or collapses during the works, public liability claims can exceed £100,000.

How long does underpinning take?

A typical 5-6m run of wall takes 4-6 weeks elapsed (mostly cure time between bays). Resin injection takes 1-3 days. Mini-piled solutions take 1-3 weeks. Insurance subsidence claims from first report to completion typically take 3-12 months including monitoring, engineer specification and works.

Does underpinning add value to a house?

It does not add value relative to a non-underpinned equivalent property. Underpinned houses are sold with a buildings insurance flag and may face higher premiums or restricted insurer choice. The underpinning restores value lost to the subsidence damage, but does not improve on the original.

Regulations & Standards

• Building Regulations 2010 — Part A (Structure), Part C (Site preparation and resistance to contaminants and moisture)

• BS EN 1997 Eurocode 7 — Geotechnical design

• BS 8004:2015 — Code of practice for foundations

• BS 8500-1/-2 — Concrete; specification and constituent materials

• CDM 2015 — Construction Design and Management Regulations; notifiable thresholds and F10 notification

• Party Wall etc. Act 1996 — Notices and awards under Sections 1, 2 and 6

• NHBC Standards Chapter 4.6 — Vibration, ground movement and trees

• BRE Digest 240/241/242 — Low-rise buildings on shrinkable clay soils

• Approved Document A — Structure — Building Regulations

• Approved Document C — Site preparation and contaminants

• HSE — Construction excavation guidance

• Property Care Association — subsidence and structural — trade body for specialist contractors

• Institution of Structural Engineers — finding a structural engineer

• BRE — building advice on subsidence — research and best practice

• basement conversion pricing guide — full basement formation including underpinning

• single storey extension pricing guide — foundation pricing for new builds

• cavity wall tie failure — related diagnosis of wall distress

• structural engineers report guide — engineer reports and their scope

• party wall act notice — Party Wall notices for underpinning