Most cracks in the walls of a British home are harmless, but a small number are the first visible sign of foundation movement, and the difference is not always obvious to the eye. This guide explains how structural engineers actually judge a crack, what the London clay under much of East Ham and Newham means for your house, and when it is worth paying for a proper inspection rather than reaching for the filler.
Engineers classify cracks by width using the BRE Digest 251 scale, and it is the single most useful thing a homeowner can measure. Hairline cracks under 1mm are cosmetic. Cracks up to 5mm are usually repairable with normal redecoration and repointing. Between 5mm and 15mm, service pipes may be affected and doors and windows often stick, which is where a professional opinion becomes worthwhile. Anything over 15mm, or a crack that passes right through the wall so you can see it on both faces, needs a structural engineer promptly.
Measure at the widest point with a crack gauge or a steel rule and write the date and width on a piece of masking tape next to it. A crack that stays the same width over six to twelve months is generally settled and stable. One that widens by more than about 1mm across a summer is telling you something is still moving.
Fine cracks along the line of plasterboard joints, around new plaster, or where a ceiling meets a wall are almost always shrinkage as materials dry out or the building warms and cools. Victorian and Edwardian terraces across East Ham, Plaistow and Forest Gate are full of these, and they reappear after every redecoration.
Small vertical cracks above windows and doors in the mortar joints are also common in older brickwork and are typically down to lintel corrosion or slight thermal movement rather than foundation failure. Cracks that follow a straight mortar joint horizontally at first-floor level on a rendered house are often just the render itself, not the wall behind it.
The pattern engineers look for first is a diagonal stepped crack running through the brick and mortar joints, wider at the top than the bottom, often near a corner or close to a large tree. That tapering shape is the signature of one part of the foundation dropping relative to the rest, which in East London usually means shrinkable clay subsoil losing moisture in a dry summer. The same crack frequently shows on the inside as a diagonal line from the corner of a window or door.
Other warning signs are cracks that appear suddenly after a hot, dry spell, cracks wider than 5mm at ground-floor level, floors that have started to slope, skirting boards pulling away from the wall, and doors that no longer close. A crack near a drain run that gets worse after heavy rain can point to a leaking or collapsed drain washing out the ground beneath the footing, which is a common and very fixable cause in Newham's older housing.
Extensions and conservatories deserve a special mention. Where a newer addition meets the original house, a vertical crack at the junction is normal if a proper movement joint exists, but a widening or stepped crack there can mean the shallower foundation of the extension is settling at a different rate. This is one of the most frequent calls we get in the borough.
A first visit is usually one to two hours. The engineer records the crack widths, checks for level and plumb, looks at trees, drains and ground levels outside, and notes the age and construction of the house. For many properties that is enough to say the movement is historic and stable, and the written report can be passed to a buyer, lender or insurer. Fees for a single-issue crack inspection in East London typically fall somewhere in the low hundreds of pounds, depending on the size of the property and whether a full report is needed.
Where the cause is not clear, the next step is monitoring. Tell-tale gauges or studs are fixed across the cracks and read every few weeks, usually over at least one summer and winter, because clay shrinks in August and swells back in February. Trial pits, a CCTV drain survey and a soil test may follow if the readings keep climbing. Only a small proportion of monitored houses go on to need underpinning, and in many cases the fix is drain repair, tree management or a resin injection rather than the full excavation people fear.
If you suspect active subsidence, contact your buildings insurer before commissioning repairs, as most UK policies cover it subject to an excess that is commonly £1,000. Insurers will normally appoint their own engineer, but an independent report is still valuable if you disagree with their findings or the claim is declined.
If you are buying a house and the RICS survey flags cracking, a specific structural engineer's report will usually settle the question and is far cheaper than walking away from a property that is actually sound. If you are selling and there is a history of movement, a completion certificate and monitoring records make the sale much smoother.
Yes, most older terraces in Newham have some cracking from historic settlement and seasonal clay movement. The concern is not the presence of cracks but whether they are wider than 5mm, stepped and diagonal, or still getting bigger.
If it is hairline and not changing, a year of your own dated measurements is fine. If it is over 5mm, appeared suddenly, or is accompanied by sticking doors or sloping floors, do not wait, as early advice is cheaper than a delayed repair.
No, underpinning is the last resort and is needed in only a minority of subsidence cases. Repairing leaking drains, managing nearby trees or simply stitching and repointing a stable crack resolves most problems at a fraction of the cost.