Underpinning: When a House Needs It, and What It Involves

Cracks that matter and cracks that do not

Fine hairline cracking at wall-to-ceiling junctions, around window reveals or where an extension meets an older wall is usually thermal movement or shrinkage. It reopens seasonally, it is rarely wider than a pound coin's thickness, and it is a decorating issue.

Cracks that warrant investigation are wider than about five millimetres, diagonal, wider at one end than the other, visible on both the inside and outside of the same wall, and accompanied by doors and windows that have started to bind. Age matters too: a crack that has been there since the 1980s is historic, while one that appeared last summer is live.

Diagonal and tapering, not vertical and uniform · Traceable through the wall from inside to outside · Getting measurably wider over weeks or months · Concentrated near a large tree, a drain run or a boundary · Accompanied by sloping floors or sticking doors

Establish the cause before anyone quotes

The single most common cause of domestic subsidence in the South East is clay shrinkage, often driven by a mature tree or a leaking drain drawing moisture from the ground. If the cause is a cracked drain, the repair is the drain. If the cause is a tree, management or removal may stabilise the ground without touching the foundations.

Proper diagnosis means a drainage survey, a site investigation with trial pits, and level monitoring across at least one full seasonal cycle. Underpinning specified without that evidence is guesswork with a large invoice attached.

The methods, and what they involve

There is no single underpinning technique. The right one depends on depth, soil type, access and the load of the structure above.

Underpinning methods and indicative UK cost ranges (2026). Method | Indicative cost | Best suited to. Mass concrete (traditional pin and bay) — £1,500 – £2,500 per linear metre — Shallow foundations, good access, modest depths; Beam and base — £2,000 – £3,500 per linear metre — Longer runs where load can be spread between bases; Mini piled underpinning — £2,500 – £4,500 per linear metre — Deep clay, restricted access, high loads; Resin injection ground stabilisation — £5,000 – £15,000 per property — Loose or washed-out granular soils, not deep clay; Typical whole-property scheme — £25,000 – £60,000+ — Where several elevations are affected Ranges exclude professional fees, monitoring, drainage repairs, redecoration and temporary accommodation.

Insurance, and why you should call them first

Subsidence is a standard peril on most UK buildings policies, with an excess typically around £1,000. If you believe you have subsidence, notify your insurer before commissioning remedial work. They will appoint a loss adjuster and usually their own engineer, and work carried out beforehand is frequently not reimbursed.

Expect monitoring to run for six to twelve months before any decision. That feels slow, but it protects you: a property monitored through a wet winter and a dry summer produces evidence, and evidence is what prevents an unnecessary scheme.

What underpinning does to a property's value and saleability

A completed, properly documented scheme with a structural engineer's certificate is far better than an undiagnosed crack. Buyers and their lenders are cautious about any subsidence history, and some insurers will price a policy higher afterwards, but a clear paper trail keeps a property mortgageable.

Keep everything: the site investigation, the monitoring data, the engineer's design, building control sign-off and the completion certificate. That folder is worth real money at sale.

The alternatives worth exhausting first

Repair defective drainage. Manage or remove the offending vegetation with arboricultural advice, remembering that removing a large tree from shrinkable clay can cause heave, which is its own problem. Improve surface water drainage away from the foundations. Then re-monitor.

In a meaningful proportion of cases, addressing the cause stabilises the building and the remaining work becomes crack stitching, repointing and redecoration rather than foundation work.

Frequently asked questions

How do I know if it is subsidence or just settlement?

Settlement happens in the first few years after construction and then stops. Subsidence is ongoing ground movement, typically seasonal, and it shows as diagonal tapering cracks that widen over time. Monitoring distinguishes them.

Will my insurer pay for underpinning?

Usually, where subsidence is confirmed and the policy is in force, subject to the excess. Notify them before starting any work, or you risk paying for it yourself.

How long does underpinning take?

A single elevation typically takes three to six weeks on site. A whole-property scheme can run to several months, and monitoring beforehand often takes longer than the work itself.

Can I live in the house during the work?

Often yes for a single elevation, with disruption confined to that area. Extensive schemes with internal excavation usually require moving out.