How to Price Subsidence Repair: Investigation, Underpinning and Margin Guide

Quick Answer: UK subsidence repair varies massively by cause and method: cosmetic crack repairs £500-2,500; full-house underpinning £15,000-80,000+; resin injection (geopolymer ground stabilisation) £8,000-30,000 typical. Most domestic subsidence cases run through the homeowner's buildings insurance — the contractor's quote sits within a loss-adjuster-controlled process. Direct-pay (non-insurance) work is a small but premium-margin slice for established specialist contractors with structural engineer relationships.

Summary

Subsidence repair sits at one of the most complex intersections in residential construction: structural engineering, ground investigation, monitoring, insurance loss-adjusting, and remedial works. It is not a job for general builders to enter casually. Most genuine subsidence cases run through the homeowner's buildings insurance (which has subsidence as a peril most policies cover), under a loss-adjuster-managed process that controls method choice, contractor selection, and pricing. The non-insurance market — cash-pay private work — exists but is small and concentrated in specialist contractors.

This guide is written for the small builder, structural engineer, or specialist contractor who wants to understand pricing structures in this market and the gating decisions (when to refer, when to investigate, when to repair vs underpin). The aim is to help correctly scope and price work and avoid the classic catastrophic loss of doing structural remedial work outside competence.

For diagnostic see condensation vs leak diagnosis (analogous diagnostic framework — for damp, not subsidence). For wider compliance see cdm 2015 domestic projects. For trade body context see cavity wall tie types.

Key Facts

Quick Reference Table

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Stage / scope Typical cost
Initial structural engineer site visit £400-900
Detailed structural survey + report £800-1,800
Soil investigation (trial pits / boreholes) £500-3,000
CCTV drain survey £150-400
12-month crack monitoring £600-1,800
Tree management (TPO check, work) £400-3,000
Cosmetic crack repair + redecoration £800-3,500
Root barrier installation (per metre) £180-350/lin m
Drainage repair / re-laying £2,500-15,000
Resin injection (geopolymer stabilisation) £8,000-30,000
Traditional mass concrete underpinning (bay) £1,500-3,500 per bay
Full-house underpinning (mass concrete) £20,000-80,000
Mini-piling (where deep strata required) £20,000-100,000+
Post-repair monitoring (2-5 years) £400-1,500/year

Pricing for typical residential properties; commercial and unusual structures vary widely. All figures exclude VAT.

Detailed Guidance

Diagnosis before remedy

Subsidence work begins with diagnosis. Symptoms (cracks in masonry, doors/windows binding, sloping floors) are the start, not the conclusion. Specific diagnostic steps:

1. Visual structural survey
   - Crack patterns (diagonal cracks at openings, stepped through brick courses)
   - Crack width and direction
   - External vs internal manifestation
   - Recent vs historic cracking

2. Site investigation
   - Soil type (clay, sandy, made ground)
   - Bearing strata depth
   - Groundwater level
   - Vegetation (mature trees within 1H of the building)

3. Drainage investigation
   - CCTV of foul and surface water drains
   - Manhole inspection
   - Look for leakage washing out fines below footings

4. Monitoring
   - Tell-tales across cracks
   - Monthly readings minimum
   - Soil moisture monitoring (clay sites)
   - Continue for 12 months typically to establish movement is active

The most common diagnostic error is treating cracks as subsidence when they're actually thermal movement, settlement of new construction, or sulfate attack. A structural engineer's signed report is the gating document for any major remedial work.

Tree-related clay shrinkage — the dominant cause

In Southern and South-East England, clay soils with mature trees are the dominant cause of residential subsidence. Clay shrinks when dewatered (typically dry summers + thirsty tree roots), foundations move down into shrunken soil, building moves. Diagnosis often follows a hot dry summer.

Management options:

The right answer depends on tree species (some are far more aggressive than others — oak, willow, poplar most problematic; horse chestnut, beech moderate), property value, customer's attachment to the tree, and TPO status.

Drainage-related subsidence

Leaking foul drains can wash fines out from below foundations, creating voids and subsidence. Diagnosis via CCTV survey + dye testing. Repair the drains and the subsidence often stabilises without underpinning.

Resin injection — the modern alternative

Geopolymer / expanding resin injection (TREVI, URETEK, Geobear systems and similar) injects expanding resin under foundations. Resin compacts the soil, supports the foundation, and lifts modestly (sometimes used for releveling).

Suited to:

Less suited to:

Cost £8,000-30,000 typical for residential. Faster than traditional underpinning (1-3 days on site vs 4-8 weeks). Insurance loss adjusters increasingly accept this method.

Traditional mass concrete underpinning

The classic remedy: excavate alongside foundation in 1m bays, dig down to competent strata, concrete back up to existing footing. Done in sequence so the building remains supported.

Process per bay:

  1. Excavate adjacent ground to expose existing footing
  2. Hand-dig down to required depth (engineer's design)
  3. Form work, place reinforcement
  4. Pour mass concrete to within 100mm of existing footing
  5. Dry-pack the final gap to existing footing
  6. Backfill
  7. Move to next bay (typically 2 bays ahead of last completed)

Typical bay size 1-1.5m wide; full house of 30m perimeter = 20-30 bays. At £1,500-3,500 per bay, full underpinning is £30,000-100,000.

Slow, disruptive, requires significant excavation, but suits a wide range of conditions and has decades of proven performance.

Mini-piling

For cases requiring load transfer to deep competent strata (e.g. fill sites, mining areas), mini-piles drilled to depth and a reinforced beam constructed between pile heads carrying the existing foundation. Engineered solution, specialist contractor, premium cost £20,000-100,000+ depending on pile count.

The insurance route

Most genuine subsidence cases run via the homeowner's buildings insurance. The process:

1. Homeowner notices cracks, reports to insurer
2. Insurer sends loss adjuster
3. Loss adjuster engages structural engineer
4. Engineer surveys, opens trial pits, often CCTV drains
5. Period of monitoring (3-12 months)
6. Engineer specifies remedial method
7. Loss adjuster appoints contractor (often from a panel)
8. Contractor executes works under engineer's supervision
9. Post-completion monitoring 2-5 years
10. Subsidence-resolved certificate issued

The contractor's role in this process is execution — pricing is often controlled by the panel rate. Margins are 15-25% net; volume drives profitability for specialist firms. Building a relationship with 2-3 loss adjusters is the route into this work.

The direct-pay route

Customers paying directly (no insurance claim) typically have either: insurance refused for a pre-existing condition; no buildings insurance; or excess too high. Premium-margin opportunity for established contractors with structural engineer relationships.

Worked example: tree-related clay subsidence, single bay underpin + drainage repair

Customer: 1930s semi, oak tree at boundary, diagonal cracking at front corner of property, drainage leakage confirmed. Insurance covering, loss adjuster engaged.

Structural engineer initial survey                       £750
Soil investigation (trial pits × 2)                     £1,800
CCTV drain survey (loss adjuster's cost)                £350
6-month monitoring period
  Tell-tales × 4                                        £400
  Monthly readings + report                            £1,200
Engineer's specification report                          £900
Drainage repair (replace lateral drain 8m)
  Excavation                                            £600
  Drainage pipe and fittings                            £350
  Reinstatement                                         £400
  Drainage subtotal                                  £1,350
Mass concrete underpinning — 4 bays at front corner
  Excavation, formwork, concrete, backfill
  4 bays × £2,800/bay                                £11,200
Post-repair tree management (oak crown reduction)        £1,200
Internal redecoration (allowable cosmetic repair)      £2,500
Post-completion 2-year monitoring
  Tell-tale readings annually                           £600
                                                       -------
Subtotal direct cost                                   £22,250
Overhead (12%)                                         £2,670
Profit (18%)                                           £4,486
                                                       -------
Contractor's invoice to insurance                      £29,406

This represents the contractor's view of one job. The homeowner's excess (£1,000 typical) is paid by them; the rest comes from the insurer. Loss-adjuster-controlled panel work might prescribe lower pricing per bay — typical panel rate £1,800-2,400/bay vs the £2,800 above.

When to refer rather than quote

Refer to a specialist underpinning contractor / structural engineer if:

Quoting for major subsidence work without competence is professional indemnity exposure (your PI insurance may exclude structural work), warranty exposure (10-year warranty on remedial work is common), and reputation exposure (a failed subsidence repair leaves the customer worse off than before).

Margin traps

  1. No structural engineer involvement. Contractor specifying their own remedial method is incompetent and uninsured. Always work to engineer's signed design.
  2. Cause not addressed. Repairing the symptom (cracks) without fixing the cause (tree, drainage, soil) leaves the property to fail again in 5-10 years. Warranty disaster.
  3. TPO tree removal. Removing a protected tree without consent is a criminal offence. Always check TPO status.
  4. Heave risk after tree removal. Removing the tree in clay can cause heave (upward movement) over 5-15 years. Sometimes worse than the original subsidence. Engineer must consider this.
  5. Insurance panel rates. Don't quote insurance work expecting cash-pay rates. Panel rates are tighter; volume matters.
  6. No post-repair monitoring. A 2-5 year monitoring contract is standard. Build it into pricing.
  7. Internal redecoration. Insurance typically covers cosmetic repairs but excludes upgrades. Specify like-for-like.
  8. Adjacent buildings. Underpinning party-wall properties triggers Party Wall Act notices. Build into programme. See party wall notice templates.

Adjacent products

Frequently Asked Questions

Is subsidence covered by insurance?

Most standard UK buildings insurance policies include subsidence as a covered peril, with a typical £1,000 excess and a requirement for the homeowner to report at the first signs. Some pre-existing subsidence properties are insured at standard terms with a record of remediation; others carry exclusions.

How long does a subsidence claim take?

Typically 6-24 months from first reporting to repair completion. Monitoring period (often 12 months) is the long lead.

Can the homeowner refuse the engineer's recommendation?

Yes but at risk to the claim. If the homeowner instructs work that doesn't address the cause, the insurer may decline future claims related to the property.

What's the difference between resin injection and underpinning?

Resin injection compacts existing soil under the foundation; underpinning physically extends the foundation to a deeper level. Resin is faster, less disruptive, often cheaper; underpinning is more universally applicable and longer-track-record.

Can I just fill the cracks?

Only if monitoring confirms movement has ceased. Filling active cracks gives short-term cosmetic improvement and confirms the issue is still active when the crack reopens.

What about heave?

Heave (upward soil movement, often following tree removal in clay) is a related and equally serious problem. Diagnosis is via the same monitoring framework. Repair methods differ — heave often requires "compressible material" or "slip planes" to accommodate ongoing soil expansion.

How much value does subsidence take off a property?

5-20% typical for a resolved case; more for an active case. The Certificate of Structural Adequacy issued post-repair restores most value but the property carries the subsidence record on its sale history.

Should I quote without a structural engineer's report?

No. The engineer's report is the contract specification — without it you have no defined scope, no warranty boundary, and personal exposure for any failure.

What about minor cracks — are they always subsidence?

No. Most cracks in domestic property are thermal movement, lintel deflection, settlement of new construction, sulfate attack on Portland cement mortars, or moisture-related plaster cracking. Genuine subsidence crack patterns are specific (diagonal, stepped through brick courses, internal+external in matching locations, progressive over time).

Regulations & Standards