Wall and Brick Cracks

Houses crack. Drywall shrinks as it cures, framing lumber moves with humidity, and a brick veneer expands and contracts with the temperature outside. A hairline over a door frame, a fine seam where two sheets of drywall meet, a gap that opens at a corner in August and closes again by March — these are ordinary, and in a climate with our moisture swings they are close to universal.

What matters is not whether a crack exists but what shape it takes, how wide it is, and whether it is going anywhere. A crack that has looked exactly the same for six years is telling you something very different from one that was not there in the spring.

A few things make a crack more interesting than the average one:

• Diagonal cracks from the corner of a door or window. Openings are the weak point in any wall, so when a wall is pulled out of square, the corners of its openings are usually where it shows first.
• Cracks noticeably wider at one end than the other. A crack that tapers is more consistent with one part of a wall moving relative to another than with material shrinkage, which tends to open fairly evenly along its length.
• The same crack on both sides of one wall, or a wall crack that lines up with one in the ceiling or the floor above.
• A crack that arrived alongside something else. A door on the same wall that stopped latching in the same season is a more meaningful combination than either sign alone.

As a rough field guide, a crack you cannot get a fingernail into is usually cosmetic. Treat that as a prompt for your own observation rather than a diagnostic threshold — width on its own has never been enough to tell anyone what is happening under a slab.

Brick veneer cracks along its mortar joints, because the mortar is weaker than the brick. That is what produces the stair-step pattern people recognise, and a stair-step crack is not automatically a foundation problem. It means one part of the wall has moved relative to another, and the reasons for that run from ordinary thermal movement, to a steel lintel rusting and expanding over a window opening, to genuine settlement underneath.

The details that make one worth following up: it widens toward the top or the bottom rather than staying parallel; brick courses no longer line up across the gap; the joint between brick and a window frame or the roofline has opened; or the same wall has separated in more than one place.

In much of the eastern Metroplex the ground itself cracks on a seasonal schedule. The USDA's official description of Houston Black — the dark, high-plasticity clay under much of Dallas and Collin counties — records that cracks between half an inch and four inches wide open from the surface down to twelve inches or more, and stay open for 90 to 150 cumulative days in most years[1]. The same document classifies the series as a Vertisol, the soil order defined by exactly this shrink-and-swell behaviour.

A house sitting on soil that does that is not sitting on something static. Cracks in the walls above often follow the same rhythm: opening through a dry late summer, closing after a wet winter. That reversal is one reason a single look in August tells you less than the same wall photographed twice, six months apart.

It is also why a crack that does not close again is worth more attention than a wide one that does.

The most useful thing you can do costs nothing: date it. Photograph the crack with something in frame for scale — a coin, a tape measure — and note the date. Do the same in the opposite season. Two dated photographs six months apart are more informative than any single measurement, and they are the one piece of evidence no contractor can produce for you retroactively.

It is also worth knowing what is under your house. The NRCS Web Soil Survey lets you draw your own property boundary and pull the soil map unit for it[2], which will tell you whether you are on one of the high-shrink-swell clays or something more forgiving.

If several signs are showing up together rather than one crack on its own, that combination matters more than any of them individually, and it is the point where an opinion from someone who does this work is worth having. The symptom check walks through what you are seeing and sorts it into what is ordinary, what is worth watching, and what is worth a call.

No single crack proves a foundation problem, and nobody can tell you what is happening under your slab from a photograph — including us. This page exists to help you describe what you are seeing accurately, not to substitute for someone standing in the room.