Every dry summer, the same conversation plays out across Bromley. A homeowner notices a new crack above the bay window or a door that's stopped closing properly, and the worry sets in. Is this subsidence? Will the insurer cover it? Do we need underpinning?
Most of the time the answer is more nuanced than the panic suggests. Real, active subsidence has a specific pattern. Cosmetic settlement looks similar but behaves differently. Here's how a specialist tells the two apart, and what to do if you suspect the worst.
The classic warning signs
Diagonal cracks wider than about 3mm running across brickwork or rendering, usually starting at a window or door corner. Cracks that taper, wider at the top than the bottom. Doors and windows that have started sticking in the last twelve months. Floors that slope enough to roll a marble across. Gaps opening up between skirtings and the floor. Tile cracks that follow the line of a wall above. Any one of these in isolation might be nothing. Two or three together, on the same elevation of the house, points to active movement.
Why Bromley has more than its share
Most of the borough sits on London clay. Clay shrinks dramatically when it dries and swells back when it rehydrates, and the difference between a wet winter and a hot dry summer can move a foundation up and down by several millimetres each year. Add a thirsty tree close to the house, or a leaking drain that's been quietly washing soil away under a corner, and you have the recipe for the kind of subsidence we see in our subsidence repair work every season.
What you should and shouldn't do first
Don't redecorate over the cracks. The pattern of cracking is the most useful diagnostic information a surveyor has. Don't immediately call your insurer either, because raising a subsidence claim before you know whether you actually have it can affect your premium for years. Do photograph the cracks with a coin in shot for scale, and date the photos. Do check whether there's a drain leak or a tree's roots running near the affected wall.
Then get an independent opinion. A specialist foundation repair survey costs less than most people expect, gives you a clear answer, and gives you the documentation you'll need if you do decide to claim. The specialists matched through this site cover Bromley, Beckenham, Chislehurst and the surrounding boroughs.
What a proper repair looks like
If active movement is confirmed, the fix depends entirely on what's causing it. A leaking drain gets repaired and the ground stabilises. A tree might be pruned, root-barriered or removed. The foundation itself might be strengthened with resin injection for shallow problems or traditional underpinning for deeper, more serious movement. Where settlement has tilted the structure, house levelling brings it back true.
The worst outcome is jumping straight to underpinning when the real issue is a £400 drainage repair. The second worst is patching up cosmetically and ignoring active movement that gets steadily more expensive to fix. The right move is a survey first, then the smallest repair that actually solves the problem.