Most cracks in a Brighton home are nothing to lose sleep over. But the city sits on an awkward mix of chalk, clay-with-flints and valley deposits, and a lot of our housing stock was built before anyone worried much about what was under it. This guide explains how to tell the difference between cosmetic movement and a genuine foundation problem, and what happens next if it is the latter.
Brighton and Hove is built on Upper Chalk, which is usually excellent bearing ground. The complication is everything sitting on top of it. The Lewes Road and London Road valleys are filled with head deposits and brickearth, which are softer and far more variable. Parts of Hanover, Elm Grove and Whitehawk are on sloping ground with shallow made ground from Victorian terracing. Closer to the seafront, and around old chalk pits and backfilled wells, you can hit made ground that was never engineered to carry anything.
This matters because a typical 1880s Brighton terrace often sits on a corbelled brick or flint footing barely 400 to 600mm deep. That was fine for 140 years of stable conditions. It becomes marginal when a large plane or sycamore starts drawing water from a clay pocket in a dry summer, when a drain leaks and washes fines out of the ground, or when a neighbour digs a basement or a deep extension next door.
Fine hairline cracking around new plaster, doors that stick only in damp weather, and stepped cracking that has been painted over three times and never moved again are usually not structural. The pattern that should prompt a call is progressive.
If you see any of the following, get a structural engineer to inspect before you get a builder to quote. A builder quoting underpinning without an engineer's diagnosis is a warning sign in itself.
Investigation comes first. Trial holes to expose and record the existing footing, plus a soil sample, typically run £700 to £1,800. A structural engineer's report is often £500 to £1,200. A CCTV drain survey is around £150 to £400 and frequently finds the real cause, in which case a drain repair costs a fraction of any foundation work.
If underpinning is genuinely needed, traditional mass concrete underpinning is done in short hit-and-miss bays, usually around 1m wide, and commonly costs somewhere in the region of £1,500 to £3,500 per bay depending on depth and access. A full elevation can therefore run well into five figures. Where access is tight, as it is in most Brighton terraces with no side return, mini-piling with a needle beam may be the only workable method and costs more again. Every one of these numbers moves with depth, ground conditions and how much of the house is affected, so treat them as a starting point rather than a quote.
For new work rather than repair, extension foundations here are usually trench fill. Expect 900mm to 1.2m deep in ordinary ground, and 1.5m to 3m where mature trees are within influencing distance, with compressible board to the trench side if the soil is shrinkable.
If you suspect subsidence, notify your buildings insurer before commissioning remedial work. Subsidence is normally covered, with an excess of around £1,000, and insurers will appoint their own loss adjuster and engineer. Paying for underpinning yourself and claiming afterwards rarely goes well.
Foundation work is notifiable to Brighton and Hove building control, and the excavation must be inspected before concrete is poured. Because so much of the city is terraced or semi-detached, the Party Wall etc. Act 1996 almost always applies. Excavating within 3m of a neighbour's structure and deeper than their foundations requires written notice, with one month before work starts. Serve it early and properly. Sorting this out after a neighbour objects costs far more in delay than doing it at the outset.
Ask who designed the scheme and whether an engineer will inspect the works. Ask how the property will be temporarily supported while bays are open. Ask whether the price includes spoil removal, which is significant in central Brighton where there is nowhere to store muck away and permits are needed for skips and grab lorries on the highway. Ask how long the sequence will take, because underpinning in bays is slow by design and anyone promising an elevation in a week is not doing it correctly.
No. The large majority of cracking is thermal movement, plaster shrinkage or old settlement that stopped decades ago. The concerning pattern is a diagonal crack wider than about 3mm that is measurably getting worse.
Repairs and underpinning to an existing house do not normally need planning permission, though they are notifiable to building control. Listed buildings and properties in one of the city's conservation areas can be different, so check before starting.
Not necessarily, and it can make matters worse through heave in clay soils. Crown reduction and a managed pruning cycle is often the better answer, and many mature trees in Brighton are protected by a Tree Preservation Order or by conservation area status anyway.
Tell us what you are planning and we will come and take a look. Free, no-pressure quotes across Brighton and Sussex.