Monitor over time
Track a foundation crack's width over time and see whether it's stable or getting worse. The rate of movement is what matters, and it's the one thing crack-gauge sellers and 'when to worry' articles never compute for you.
What it does
This tool organizes your readings. It does not diagnose structural safety or replace an inspection.
Why monitor
A single measurement can't tell you whether a crack is a settled, cosmetic line or the early sign of ongoing movement. What separates the two is how the width changes over weeks and months. A crack that holds steady across several readings is usually far less urgent than one that widens a little each time — even if the second one looks smaller today.
That's the whole point of a log. Record the same spot on a schedule, and the pattern becomes obvious: flat means stable, a rising line means it's moving. This tool does that math for you and reads it against the width and the crack type, without ever claiming your foundation is safe, failing, or repaired — those are decisions for an in-person review.
How to measure it
Draw a short pencil line across the crack, or fit a crack gauge, so you measure the exact same spot every time. Movement is only meaningful if the reference point doesn't move.
A crack gauge, calipers, or a ruler all work — just don't switch between them. Record the width in the same unit (mm or inches) each reading.
Log the date with each width, and take a photo with the date visible. The photo backs up the numbers and helps a professional later.
Every three to six months is a good baseline, plus a reading after heavy rain or drought, or when new symptoms show up.
Know the type
Thin vertical cracks are the most common and usually the least urgent. Diagonal cracks can follow settlement. Horizontal and stair-stepcracks are the ones to take seriously — they can signal soil pressure or wall movement, and they warrant a professional look regardless of how slowly they're changing. Set the type in the log and the read adjusts accordingly.
Thresholds
The width thresholds the log reads your measurements against, published so you can check a crack against them before you start a log. Width alone never settles it — a hairline crack that appeared last month matters more than a wider one that hasn't moved in a decade — but it is where most people start.
| Crack width | On a gauge | What it usually means |
|---|---|---|
| Under 1/8" | Under 3 mm | Thin. Common in poured walls as shrinkage. Log it, and re-measure the same spot every few months. |
| 1/8" to 1/4" | 3–6 mm | Worth watching closely. Measure monthly rather than seasonally, and note whether water comes through. |
| Over 1/4" | Over 6 mm | Past the width where a professional look is usually advised, even if the readings are holding steady. |
Thresholds
Rate is the number every page on this topic says matters and almost none compute. Log two dated readings above and the tool works it out; these are the bands it sorts the result into.
| Rate of widening | What it usually means |
|---|---|
| Under 0.3 mm per month | Holding steady between readings. Keep logging every few months, and after heavy rain or drought. |
| 0.3–1 mm per month | Slowly widening. Shorten the interval to monthly and watch whether the pace holds or picks up. |
| 1 mm per month or more | Actively widening. Worth a foundation contractor or structural engineer looking at it, rather than watching alone. |
Horizontal and stair-step cracks warrant a professional look regardless of how slowly they are changing, and so does any crack already past 1/4 inch. Nothing here is a diagnosis — it organises what your readings show.
FAQ
Mark a fixed spot across the crack (a pencil line on each side, or a crack gauge), measure the width at that same spot, and log the date and width here every three to six months. The log tracks the readings and shows the rate of change, which matters more than any single measurement.
The signal is the rate of change between readings, not the width alone. If the width holds steady over several readings, the crack is stable; if it climbs month over month, it's actively moving. This tool computes that rate and flags widening for you.
As a rough guide, a crack over about 1/8 inch is worth watching closely, and one over 1/4 inch usually warrants a professional look. Width isn't the only factor, though — crack type and whether it's moving matter just as much.
Generally yes. Horizontal and stair-step cracks can point to soil pressure or movement in the wall and are worth a professional review regardless of how fast they're changing, especially alongside bowing, leaning, or water. Most thin vertical cracks are less urgent, but still worth logging.
Every three to six months is a reasonable baseline, plus an extra reading after heavy rain or drought, or whenever new symptoms appear — sticking doors, gaps at trim, or uneven floors. Measure more often if the log shows the crack slowly widening.
A crack gauge is ideal, but calipers or even a ruler at a marked point work as long as you're consistent — same spot, same tool, each time. Photograph the crack with the date visible, so you have a visual record alongside the numbers.
Reach out when a crack is widening, horizontal, stair-stepped, leaking, or displaced, or when several symptoms appear together. A foundation contractor can explain options; a structural engineer is useful for an independent opinion on expensive or conflicting recommendations. This tool organizes your observations — it does not diagnose your foundation.
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