Underpinning in London

Most people who search for underpinning have found a crack, not a diagnosis. A surveyor may have used the word in a homebuyer report. An insurer may have mentioned it on the phone. A builder may have looked at a wall and shaken his head. None of that is a finding of subsidence, and most cracking in a London house is not subsidence at all. Figures from the Royal Institution of Chartered Surveyors, reported by the HomeOwners Alliance in 2026, put the share of subsidence-affected properties that actually need underpinning at fewer than one in ten.

Underpinning is a last resort rather than a first response, and we would far rather understand the cause than fill a trench. It is expensive, disruptive, permanent, and it changes how the house is described for the rest of its life. The honest first move is diagnosis: what is moving, whether it is still moving, and why. That takes a structural engineer, usually a drain survey, and often monitoring across a full seasonal cycle. This page covers what the diagnosis costs, what the work costs if it turns out to be needed, and where a contractor fits, which is on the building side only.

How much does underpinning cost in London?

Underpinning costs £1,000 to £2,500 per linear metre of wall treated, which puts most single-elevation domestic jobs between £6,000 and £21,000, with £13,500 a common figure for a three-bedroom semi. Whole-house schemes on period property run higher, and quantity surveyor guidance puts larger projects at £10,000 to £30,000 and occasionally beyond £50,000.

Three things move the number more than anything else. The method, which is set by the engineer rather than by you or by us. The depth, because the cost of a pit rises faster than its depth. And the access, since a rear elevation reached only through a terraced hallway has to be dug and poured by hand, and London sites are frequently exactly that.

Method	Cost per linear metre	Time on site
Traditional mass concrete, pit and pour	£1,000 to £1,500	Around 6 days, each bay curing before the next is opened
Beam and base	£1,200 to £2,500	Comparable to mass concrete, plus beam casting
Mini-piled	£1,500 to £2,500	Around 5 to 6 days, plus rig delivery and access
Resin injection	£800 to £1,500	1 to 2 days, often a single day on a small house

Per linear metre rates from MyBuilder and Mainmark; upper beam and base figure costed by a quantity surveyor for Homebuilding & Renovating; project totals from MyJobQuote, 2026. Published rates are national. London labour and restricted access push most jobs to the top of every band rather than the middle.

Note that this is remedial underpinning, priced by the metre of wall. Underpinning carried out to create a new basement is a different exercise priced by floor area, and our basement conversion cost guide and the basement extension page cover that separately.

What does the total bill break down into?

The underpinning itself is most of what you spend, and the rest is investigation, design, statutory fees and putting the house back together. Homeowners are most often caught out by the front end, because the engineer, the trial pits and the drain survey all have to be paid for before anyone knows whether the work is needed at all.

Element	Typical cost	Who provides it
Structural engineer, first inspection and report	£200 to £1,500	Independent structural engineer
Site investigation, trial pits and soil testing	£500 to £1,000	Ground investigation contractor
CCTV drain survey	£90 to £500, around £250 typical	Drainage contractor
Monitoring across a seasonal cycle	£200 to £1,000 over 6 to 12 months	Engineer or the insurer's loss adjuster
Engineer's underpinning design	£2,500 to £5,000 for a whole house	Independent structural engineer
The underpinning works	£1,000 to £2,500 per linear metre	Building contractor
Building control charge	Varies by borough, around £800 including VAT	Local authority or approved inspector
Party wall surveyor, where required	£900 to £2,700 with one agreed surveyor	Party wall surveyor
Making good, crack repair and decoration	£300 to £1,500	Building contractor

Engineer, drain survey and making good from MyJobQuote and MyBuilder; design fee from Mainmark; party wall fees from HomeOwners Alliance, 2026. The building control figure is the published domestic rate for underpinning up to 6 metres in one London borough for 2026/27. Charges are set borough by borough, so check your own.

How do you know whether you actually need it?

You do not know from the crack alone, and any contractor who tells you otherwise from the pavement is guessing. Diagnosis is a process of elimination carried out by a structural engineer, and the first job is to rule out the far more common causes of cracking.

The National House Building Council sets out four ordinary causes that have nothing to do with foundations. Shrinkage happens as mortar, plaster and concrete dry out. Thermal movement happens every year as the building expands and contracts. Moisture movement is the continual wetting and drying of materials from daily life. Settlement is a new building bedding down, which stabilises on its own. The NHBC states plainly that a crack of 2mm or less is cosmetic and will not affect structural stability.

The professional yardstick is BRE Digest 251, which classifies damage in six categories. Categories 0 to 2, up to 5mm, are aesthetic and need only redecoration. Categories 3 and 4 affect weathertightness and the operation of doors and windows. Category 5, generally above 25mm, is a stability problem and is where structural intervention becomes likely. Almost every crack a London homeowner worries about sits in category 1 or 2.

Cracking that is usually not subsidence:

• Hairline and fine cracks under 1mm in plaster only, especially after building work or a first winter of central heating
• Vertical or horizontal cracks of roughly constant width under 2mm that open in summer and close in winter
• Cracks where an external wall meets an internal plasterboard wall, or along plasterboard ceiling joints
• Cracks at skirtings, architraves and immediately around a lintel over a window or door
• Cracks in a recently built or extended property that have not grown since you first noticed them
• Regular horizontal cracking following the bed joints up a cavity wall, which commonly indicates corroded wall ties rather than ground movement

Cracking that warrants a structural engineer:

• Wider than 5mm at any point. A one pound coin is about 3mm thick and works as a field gauge
• Wide at one end and narrow at the other. The NHBC identifies this tapering pattern with subsidence and heave
• Diagonal or stepped through the mortar joints, at any width
• Visible in the same place both inside and outside the property
• Running horizontally along the damp proof course, or extending below it
• Accompanied by doors and windows that have started to stick or swing open on their own
• Noticeably wider or longer than when you first noticed it

Where ground movement is genuinely in play, the cause matters as much as the symptom. Around 70% of subsidence cases are attributed to tree roots drawing moisture from clay soil, with defective drainage, weak ground and historic mining behind the rest. A leaking drain washing fines out from under a footing is a drainage repair, not an underpinning job, and a CCTV survey at around £250 is the cheapest way to find out. Our London subsidence guide covers the diagnosis in more detail, and our guide to wall tie failure covers the cavity wall pattern above.

Which underpinning method applies to your house?

The engineer selects the method from the trial pit findings, the soil, the depth of the existing footing and the access available. There is rarely a genuine choice, and the four methods are not interchangeable.

Traditional mass concrete, also called pit and pour, is the oldest and usually the cheapest. Holes roughly a metre wide are dug beneath the wall in a sequence set by the engineer, boarded out, and filled with concrete one bay at a time. Each bay cures before the adjacent one is opened, which is why a simple method is still a slow one. It is the default for a shallow Victorian footing on stable ground.

Beam and base develops the same idea. Pits are excavated and concreted as before, but a reinforced concrete beam spans between them to spread the load of the wall above. It costs more per metre and buys stability where the ground is uneven or the bases cannot be placed continuously.

Mini-piled underpinning is used where competent ground is deep, where the soil is poor, or where the house is too heavy for mass concrete. Small-diameter piles are drilled at intervals, reinforced and grouted, then tied into the existing structure. It is normally reserved for foundations deeper than about five metres and is the most expensive method, because it needs specialist rigs and operators. Access is the practical constraint in London, since the rig has to reach the elevation.

Resin injection is the newest and least invasive. Expanding structural resin is injected through slim tubes into the soil beneath the foundation, densifying the ground and lifting the footing. Work on a typical house often takes a single day with no excavation. It is not universal, and suitability depends on the ground and the failure mode. Your engineer, and your insurer where a claim is running, decide whether it is appropriate.

What approvals does underpinning need?

Underpinning needs building control approval and, next to a shared wall, party wall notices. It does not normally need planning permission. The Planning Portal states that maintenance to foundations generally does not require permission, though you should check with the local planning authority first if the property is listed or sits in a conservation area, which covers a large share of inner London.

Building regulations are not optional. Underpinning all or part of a building's foundations is defined as building work, and the relevant standard is Part A of Schedule 1 to the Building Regulations 2010. Requirement A2 is the one that matters: a building must be constructed so that ground movement caused by swelling, shrinkage or freezing of the subsoil, or by land-slip or subsidence, will not impair the stability of any part of the building. You notify building control before work starts, the inspector reviews the engineer's design, inspections happen at stages during the work, and a completion certificate is issued at the end. Keep that certificate, because a conveyancer acting for a future buyer will ask for it, together with a Certificate of Structural Adequacy where the repair ran through an insurance claim. Our building regulations guide sets out the inspection stages.

Underpinning next to a neighbour is notifiable under the Party Wall etc. Act 1996, and two separate sections can bite. Section 2(2)(a) gives you the right to underpin a party structure, which requires a party structure notice served at least two months before work begins. Section 6 covers the excavation itself: section 6(1) applies where you excavate within 3 metres of a neighbouring building and deeper than the bottom of their foundations, and section 6(2) applies within 6 metres where the excavation cuts a line drawn down at 45 degrees from the base of their foundation. Notice under section 6 must be served at least one month before you begin, and it must state whether you propose to underpin or strengthen the neighbour's foundations.

If a neighbour consents in writing, that is the end of it. If they dissent or do not reply, surveyors are appointed and an award is drawn up, and the building owner carrying out the work pays the fees. We are not party wall surveyors and cannot serve or agree these notices for you, but we build to the award once it is in place. Our Party Wall Act guide and the party wall works page cover the process.

Does insurance pay for underpinning?

Buildings insurance usually covers structural damage caused by subsidence, and most domestic underpinning in London runs through a claim rather than being paid for privately. Association of British Insurers figures published in August 2026 show insurers paid £72 million for domestic subsidence claims in the second quarter of 2026, with the average claim reaching a record £20,000, more than £2,000 above the same quarter a year earlier.

Making the claim changes who is in charge. You notify your insurer, and the insurer appoints the engineer who investigates, decides whether movement is active, sets the monitoring period and specifies the remedy. That is the correct order, and it also means you should not commission your own underpinning design before speaking to the insurer, because the scope you pay for may not be the scope they accept.

What is not covered surprises people. The standard subsidence excess is around £1,000, considerably higher than a general claims excess. Damage to garden walls, fences, gates, patios and driveways is not usually covered unless it happens at the same time as damage to the house itself. Gradual deterioration and poor original construction are excluded, as in most policies is damage from a defect you knew about and did not act on. Read the schedule rather than the summary.

Two further points are worth knowing before you start. Subsidence history has to be disclosed when you sell, with no time limit, even if the repair was completed a decade ago and has held perfectly. And an underpinned property is harder to insure and slower to sell than one where the cause was removed and the ground settled, which is another argument for exhausting the alternatives first.

What we do on an underpinning job, and what we do not do

We are a building contractor, so we build the underpinning to a structural engineer's design and coordinate the approvals around it. On a live job that means temporary support and propping before anything is opened, excavation and concreting strictly in the bay sequence the engineer specifies, backfilling and pinning as designed, and making good afterwards.

It also means the administrative work that holds a job together. Appointing an independent structural engineer if you do not already have one. Arranging trial pits so the engineer has real foundation data rather than an assumption. Booking building control inspections at each stage so the completion certificate is issued cleanly. Working to a party wall award where one is in place.

We do not produce structural calculations. We are not structural engineers, surveyors or party wall surveyors and we do not hold ourselves out as any of them. We do not diagnose subsidence, and we will not tell you that you need underpinning, because that is not a contractor's call to make. We do not handle your insurance claim or negotiate with a loss adjuster.

If you have a crack and no diagnosis, the useful next step is a structural engineer rather than a builder. If you already have a report and a design, call us and we will price the build.