How to Monitor a Foundation Crack Over Time: A Simple Method

TL;DR: Mark both ends of the crack with a pencil line and date, then measure width and length monthly with a ruler or a $15 crack gauge. If the crack widens more than 1/8 inch within 90 days, or grows longer than 6 inches in a season, get a structural engineer to look at it before it's a $10,000 problem instead of a $500 one.

_Last reviewed: July 2026 · 7 min read_

Most homeowners find a foundation crack, stare at it for a minute, and then just hope it stays the same size. That's the wrong move. Cracks that are actively growing tell you something is shifting under your house, and the only way to know if that's happening is to track it on a schedule.

Okoniq Property Hub lets you log a crack's measurements and photos by date, so you have a clean record if you ever need to show a contractor or insurance adjuster exactly how it changed.

How do you know if a foundation crack is serious?

A crack is worth watching closely if it's wider than 1/8 inch, runs diagonally at 45 degrees, or is horizontal rather than vertical. Vertical hairline cracks under 1/16 inch are common in poured concrete and usually come from normal curing shrinkage in the first 1-2 years after the home was built.

Horizontal cracks are the ones that worry engineers most, because they often mean soil pressure is pushing the wall inward, not just settling straight down. Stair-step cracks in block or brick foundations, especially ones wider at the top or bottom than the middle, also point to uneven settlement. If you're also seeing doors that stick or gaps opening around window frames, that's a pattern worth pairing with your crack log, similar to how you'd track 5 signs of a slab leak under your floor by watching for more than one symptom at once.

What's the best way to measure a crack over time?

The simplest method costs under $20: buy a plastic crack monitor gauge, which is a two-piece overlay you screw or glue across the crack so one half stays fixed while the other moves with any shift. Read it every 30 days and write the number down with the date.

If you don't want to buy a gauge, use a fine-tip permanent marker to draw a line perpendicular to the crack at its widest point and at each end, labeling each mark with today's date. Next month, measure from your marks with a ruler and add new dates further along if the crack has lengthened. Take a photo each time with a coin or tape measure in frame for scale, since a phone photo without a reference object is nearly useless for comparison six months later.

| Method | Cost | Precision | Best for | |---|---|---|---| | Crack monitor gauge | $10-$25 | High, measures to 1mm | Cracks you suspect are active | | Pencil marks + ruler | Free | Moderate | Quick monthly checks | | Photo log with scale | Free (phone) | Low-moderate | Visual record over years |

How often should you check a foundation crack?

Check monthly for the first 3-6 months after you first notice it, then quarterly if it hasn't changed. Seasonal shifts matter here. Soil expands and contracts with moisture and freeze-thaw cycles, so a crack that looks stable in July can widen in January when the ground freezes and heaves.

Keep the checks tied to the same conditions when possible, ideally after a dry stretch of weather rather than right after heavy rain, since saturated soil can make a wall bow slightly and throw off your reading. Many owner-operators pair this with a seasonal walk-around, the same way you'd check 5 gutter jobs you're forgetting before winter, since poor drainage around the foundation is one of the top causes of new cracking in the first place.

What causes a foundation crack to keep growing?

Water is the most common driver, either from grading that slopes toward the house, gutters dumping runoff too close to the wall, or a downspout extension that's missing entirely. When soil next to the foundation gets saturated repeatedly, it expands and contracts more than dry soil, and that cycle puts uneven pressure on the wall year after year.

Tree roots within 10-15 feet of the foundation can also pull moisture out of clay soils unevenly, causing one section to settle faster than another. If you've already had downspout issues, it's worth checking [6 downspout mistakes that send water into your basement](/blog/6-downspout-mistakes-that-send-water-into-your basement) side by side with your crack log, because fixing the water problem sometimes stops the crack from growing without any structural repair at all.

What should you do once a crack is confirmed active?

Once you have 90 days of measurements showing real movement, call a structural engineer for an inspection rather than a foundation repair company first. Engineers charge $300-$700 for an assessment and have no financial stake in selling you a specific repair, while some repair companies offer "free inspections" that lean toward recommending expensive fixes like helical piers even when simple grading corrections would solve the problem. Bring your dated measurements and photos to that visit, since a documented growth pattern helps the engineer diagnose the cause faster than a single snapshot in time.

FAQ

Is a 1/4 inch foundation crack bad?

A 1/4 inch crack is wide enough to warrant a professional look, especially if it's horizontal or has grown from a smaller width within the last year. Vertical cracks under 1/4 inch that have been stable for years are often cosmetic, but width alone shouldn't be the only factor you check.

Can I fill a foundation crack myself while monitoring it?

Yes, but use a flexible polyurethane sealant rather than rigid epoxy if you're still tracking movement, since epoxy can crack again and hide new shifting. Wait until measurements show stability for at least 2-3 months before doing a permanent structural repair.

How much does foundation crack repair typically cost?

Simple epoxy injection for a stable, non-structural crack runs $300-$800 in most US markets. Active settlement requiring piers or underpinning can run $3,000-$15,000 or more depending on the foundation size and soil conditions.

Does homeowners insurance cover foundation cracks?

Standard policies usually exclude gradual settling or earth movement, but they may cover foundation damage caused by a sudden covered event like a plumbing leak or storm. Check your specific policy language and document the cause with dated photos before filing a claim.

What's a normal amount for a foundation crack to widen per year?

Less than 1/16 inch per year is generally considered normal settling in most soil types. Anything approaching 1/8 inch or more within a single year is worth a professional evaluation.

This is educational information, not structural engineering advice. Call a licensed structural engineer if a crack shows active growth or if you're unsure what's causing it.