How often should I measure a foundation crack?

Monthly, at the same marked spot, for at least a full year so you see the wet and dry seasons.

What crack width is a concern?

Around 5 mm and wider, or any crack that keeps widening. The damage scale in common engineering use puts the slight-to-moderate boundary near there.

Is a crack that opens and closes a problem?

Seasonal movement is common in clay soils. A crack that returns to the same width each year is different from one that ratchets wider.

Can I seal the crack while monitoring?

Sealing hides the change you are measuring. Monitor first, or mark and photograph before sealing a water leak.

HyreFoundation tools

Foundation crack monitoring log

Two readings at the same marked spot. The change per month says more than any single photo.

A foundation crack monitoring log records the width of the same crack, at the same marked spot, on different dates.

Enter two readings in millimetres and the days between them, and this tool gives the change per month and whether the crack grew at its tips. Cracks that open and close with the seasons are common.

Steady widening, or width near 5 mm, is the point to call a licensed structural engineer.

Foundation crack monitoring log

Two readings at the same marked spot. The change per month says more than any single photo.

— Change per month

— Change

— Length

— What it suggests

What this assumed —

Two readings show change, not a trend. Not a structural opinion.

How to keep the log

Mark the spot. Draw a short pencil line across the crack and measure there every time, with a crack-width card or feeler gauge. Mark the tips with a dated line too.

Measure monthly for a year. Concrete shrinks as it dries and moves with soil moisture. One reading cannot tell a seasonal crack from a growing one. Photograph each reading with the card in view.

Why 5 mm? In the damage scale engineers use (Burland and colleagues), crack widths up to about 5 mm fall in the slight band and wider cracks in moderate and above. Width alone is not a diagnosis, but it is the point where an engineer’s visit is worth it. See which foundation cracks matter.

Questions this calculator answers

How often should I measure a foundation crack?: Monthly, at the same marked spot, for at least a full year so you see the wet and dry seasons.
What crack width is a concern?: Around 5 mm and wider, or any crack that keeps widening. The damage scale in common engineering use puts the slight-to-moderate boundary near there.
Is a crack that opens and closes a problem?: Seasonal movement is common in clay soils. A crack that returns to the same width each year is different from one that ratchets wider.
Can I seal the crack while monitoring?: Sealing hides the change you are measuring. Monitor first, or mark and photograph before sealing a water leak.

Sources and methodology

Figures dated 26 October 2026. Last reviewed August 16, 2026.

Mair, Taylor and Burland (1996), Table 1: classification of visible damage by crack width (International Society for Soil Mechanics and Geotechnical Engineering, retrieved 2026-10-26)
TIP 17, Drying Shrinkage of Concrete (National Ready Mixed Concrete Association, retrieved 2026-10-26)
ACI 224R-01, Control of Cracking in Concrete Structures, chapter 3 (American Concrete Institute, retrieved 2026-10-26)

Which cracks matter The damage scale and its caveat.
Elevation log Floor readings over time.
Crack identification What the pattern suggests.
Normal foundation cracks Which cracks are expected.

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Foundation crack monitoring log

How to keep the log

Questions this calculator answers

Sources and methodology

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