The most important thing about a crack isn’t how it looks today — it’s whether it’s moving. A stable crack that hasn’t changed in a year is usually cosmetic; a crack that’s steadily widening is telling you the foundation is actively shifting. You can track this yourself with a few dollars of supplies: mark the ends, measure the width, and check it on a schedule. In Houston, expect some seasonal movement as clay soil swells and shrinks — the goal is to separate that normal breathing from real, progressive growth. This guide shows you how to gather that evidence so a professional can make the call.
What you'll need
- A pencil
- A ruler or tape measure
- A notepad or phone
- Painter’s tape
- A camera
Recommended parts & supplies
- Foundation crack monitor gauge — the standard tool — reads horizontal and vertical movement in mm
- Feeler gauge set — measures exact crack width in fractions of a millimeter
- Digital caliper — for precise, repeatable width readings over time
- Crack width comparator card — a cheap card to grade crack width at a glance
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Step by step
- 1
Clean the crack and mark both ends
Wipe the crack clean so you can see it clearly. With a sharp pencil, draw a small tick mark exactly at each end of the crack and write today’s date beside one of them. If the crack later grows past your mark, you’ll know instantly and by how much. Do this for each significant crack you’re watching, indoors or out.
- 2
Measure and record the width at the widest point
Find the widest part of the crack and measure it — a feeler gauge or digital caliper gives you a real number, but even a ruler works for wider cracks. Write down the width and the date. As a rough guide, hairline cracks under about one-sixteenth of an inch are usually cosmetic, while anything over a quarter inch, or a crack you can slip a coin into, deserves professional eyes.
- 3
Install a crack monitor gauge for precise tracking
For the clearest evidence, mount a foundation crack monitor gauge — an inexpensive two-part plastic card that screws or glues across the crack. One half has a grid, the other a crosshair, so as the crack moves the crosshair slides across the grid and reads out the exact movement in millimeters, both sideways and up-and-down. It removes all guesswork about whether things are changing.
- 4
Photograph it with something for scale
Take a straight-on photo with a coin, ruler, or the tape measure right beside the crack, and save it in a dated folder. Repeat from the same angle each time. A run of dated, scaled photos is compelling evidence for an inspector and helps you see slow changes your eye would miss month to month.
- 5
Check on a schedule and log every reading
Check your marks, measurements, and gauge once a month, and always after a big weather swing — a heavy Houston rain after a long drought, or a hot dry spell. Keep every reading in one simple log with dates. A crack that grows a little in the dry season and closes back up when it rains is soil breathing; a crack that only ever gets wider is the one to act on.
- 6
Know the thresholds that mean “stop watching, call now”
Escalate from monitoring to a professional inspection if a crack widens noticeably over a few months, opens past a quarter inch, runs horizontally across a wall, shows one side of the crack sitting higher than the other (a shear step), or appears alongside new sticking doors and sloping floors. At that point you have enough evidence — the next step is a pro, not more measuring.
When to call a pro
Monitoring is safely DIY, but interpreting active movement and repairing it is not. Bring in a licensed foundation specialist or structural engineer once a crack is clearly growing, is wider than about a quarter inch, runs horizontally, or shows vertical offset between the two sides — and right away for any horizontal crack that is bowing inward, which can signal imminent structural failure. Do not fill or caulk a structural crack to “stop” it: sealing a moving crack hides the evidence, traps water, and does nothing to address the soil movement underneath. And never inject, patch, or pier a structural crack yourself — that’s engineered repair work. Your job is to gather the dated measurements and photos; hand those to the pro so they can move straight to a solution.
Get a free quote from a local pro
No obligation — a licensed, insured local Houston partner will reach out. Available 24/7 for emergencies.
How to Monitor a Foundation Crack (and Know If It’s Getting Worse) — FAQ
How do I know if a foundation crack is getting worse?
Is it normal for foundation cracks to open and close with the seasons?
Should I fill a foundation crack while I monitor it?
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