James Hartley
Why Older Properties Are More Prone to Subsidence
Subsidence is the downward movement of a building's foundations, and it is something that turns up far more often in older homes than in new builds. That is not simply because they have had more time to develop problems. Victorian and Edwardian houses, in particular, were often built with shallow foundations, sometimes little more than a metre deep, and on whatever ground the builder happened to find. Clay soils shrink and swell with the seasons, and a century of droughts, leaks and root growth can gradually pull the ground away from beneath one corner of a house.
The good news is that subsidence is usually a slow process. It rarely happens overnight, which means that if you know what to look for, you can spot the warning signs long before you commit to a purchase. The trick is knowing which clues matter and which are just the ordinary settling of an old building.
Diagonal Cracks: The Ones Worth Worrying About
Almost every period property has a few cracks. Hairline cracks in plaster, fine lines above door frames, and the odd bit of blown render are usually just cosmetic. What you want to look for are diagonal cracks, particularly those that step in a staircase pattern through brickwork or masonry.
Subsidence cracks tend to have a few telltale features:
- They run diagonally, often at roughly 45 degrees, usually from the corners of windows or doors.
- They are wider at one end than the other, typically wider at the top.
- They tend to be at least 3mm wide, sometimes much more.
- They appear on both the inside and outside of the same wall.
- They are often found near the corners of a building, where two walls meet.
If a crack is thin, vertical, and has been there for years without changing, it is probably not subsidence. If it is wide enough to slide a pound coin into, and it is visible on both faces of the wall, take it seriously.
Sticking Doors and Windows
One of the most reliable early signs of movement is a door or window that no longer opens or closes properly. If a door sticks in its frame, or if the gap around it has become uneven, the wall it sits in may be moving. This is especially telling when a door sticks at certain times of year and frees up later, which points to seasonal soil movement rather than something more dramatic.
Check the corners of the frames, too. Cracks radiating from the top corners of a door opening are a classic subsidence pattern. Look also at whether skirting boards have separated from the wall, or whether there is a gap between the floorboards and the skirting. These small gaps often appear before any crack becomes visible in the plaster.
Uneven Floors and Sloping Surfaces
Floors in old houses are rarely perfectly level, and a slight slope in a Victorian terrace is not necessarily a problem. But if a floor slopes noticeably towards one corner, or if you feel a distinct dip as you walk across a room, that is worth investigating. The same goes for walls that lean, or a ceiling that visibly sags.
A simple test is to place a marble or a small ball on the floor and see which way it rolls. If it heads consistently towards one external wall, that wall may be sinking. Another useful check is to look along the top of skirting boards, which should be roughly parallel to the floor. If they run uphill or downhill noticeably, the floor has moved.
Bear in mind that some movement is normal in older properties, particularly timber-framed ones, which were designed to flex. The question is whether the movement is ongoing.
Clues Outside the House
Step outside and look at the whole building. Subsidence often shows itself most clearly on the exterior, and a few minutes with a torch and a notepad can tell you a great deal.
- Drains and gullies: leaking drains soften and wash away soil beneath foundations. Look for cracked gullies, damp patches, or a sewer smell near the base of walls.
- Trees and shrubs: large trees within a few metres of the house, especially willows, poplars, oaks and leylandii, draw moisture from clay soil and can cause shrinkage. Check whether any have been removed recently, as the ground can swell back and cause heave.
- Gutters and downpipes: overflowing gutters or a broken downpipe soak the ground around the foundations, which can lead to movement in some soils.
- Brickwork and render: stepped cracks, bulging panels, or render that has cracked in a diagonal line are all worth noting.
What to Do Before You Buy
If you spot any of these signs, do not panic and do not assume the worst. Many cases of subsidence are manageable, and some are historic and no longer active. But you should not rely on a standard mortgage valuation to catch them, as these are often desktop exercises with only a brief inspection.
Instead, commission a structural survey from a qualified surveyor, ideally one with experience of period properties. Ask specifically about the foundations, the soil type, and any evidence of movement. If subsidence is confirmed, a structural engineer can advise on whether it is ongoing, what caused it, and what repairs would involve. That might mean underpinning, drain repairs, or simply managing vegetation nearby.
It is also worth asking the seller whether there is any history of movement, insurance claims, or monitoring. A honest answer here is far more useful than any crack, and it gives you a firm footing before you exchange contracts.
