Before anything else: this page tells you what patterns usually indicate and which ones deserve a proper look. It is not a structural assessment and we do not make structural determinations from descriptions or photographs. Where something warrants assessment we say so rather than reassuring you, because reassurance we are not qualified to give is worth nothing.
Start With Direction
| Pattern | Usually means | Verdict |
|---|---|---|
| Vertical / near-vertical in poured concrete | Shrinkage from curing. Very common indeed | Seal if it leaks; monitor |
| Diagonal from a window or door corner | Settlement. Common, frequently historic | Mark, date, monitor |
| Stair-step in block or brick | Settlement along the weak line of the joints | Monitor; assess if widening |
| Horizontal, part-way up | Associated with lateral soil pressure | Get it assessed |
Our crack triage tool illustrates each of these, which is considerably easier than describing them.
Then Establish Whether It Is Moving
A wide crack that has not moved in forty years is less concerning than a narrow one that has opened since spring.
- Draw a pencil line across each end and write today's date beside it
- Measure the width at the widest point — a crack gauge is a few dollars
- Photograph it with a coin or ruler in frame, same angle each time
- Run a hand across it — does one side sit proud of the other?
- Check again in three months, and again after a wet spring
- Note whether doors or windows above it have started sticking
That takes ten minutes and it is the difference between worrying about a crack indefinitely and actually knowing something about it.
The Short List
- It runs horizontally part-way up the wall
- It has widened measurably since you marked it
- One side sits proud of the other
- The wall is visibly bowing or leaning inward
- It appeared suddenly rather than being noticed
- Doors or windows above have started sticking
None of those means disaster. They mean the question has moved past what a website can usefully answer. And the cheapest version of any foundation problem is the early one, which is the honest argument for arranging a look rather than deferring it.
Different Foundations, Different Cracks
Poured concrete shrinks as it cures, so vertical hairline cracking is routine rather than alarming. Block cracks along its mortar joints, giving the stair-step pattern — and because block is hollow it is more vulnerable to lateral pressure than poured concrete, which is why the horizontal pattern matters particularly on block walls.
Fieldstone and brick are a different assessment entirely. What reads as a crack is frequently failed mortar or a displaced stone rather than a fractured wall, and the remedy is repointing — with a lime-based mortar, never hard Portland mix. What matters on stone is whether soil is washing through between stones and whether anything has moved position.
And a note on age: an 1840s farmhouse cellar has been settling for nearly two centuries. Some cracking is part of its history. Whether it is still moving is the entire question, and that is answered by marking and waiting, not by looking once.
Questions
How wide is too wide?
Width is the wrong question — movement is the right one. Plenty of old houses have settled cracks a quarter inch wide that have not changed in living memory. A hairline that has opened measurably in six months is more informative than either.
Should I fill it?
If it is leaking and stable, professional injection is the durable answer. If it is in the assess category, filling it is actively unhelpful — you have hidden the evidence you would need to judge movement, and the next person to look has nothing to go on.
My wall looks like it is bowing inward. What now?
Get it looked at properly. That is beyond what we will comment on from a description, and it is the situation where a qualified opinion is genuinely worth having rather than a contractor's reassurance. We would rather say that than give you a verdict we are not in a position to give.
Will it affect selling the house?
It can come up in an inspection, and an unexplained crack worries a buyer far more than a documented one. A dated photographic record showing no movement over three years is a genuinely useful thing to hand over — another reason to start marking it today rather than the week you list.