Most foundation cracks aren't structural. Concrete shrinks as it cures, soil expands and contracts seasonally, and small cracks appear in most homes within the first few years. The question that matters: is the crack stable, or is it growing? A 1/16-inch crack you've watched for 5 years is different from a 1/16-inch crack that wasn't there last month. The monitoring process is dead simple. Two pencil marks, a date, a phone camera, and a yearly check.
Quick reference: when to worry
- Hairline (under 1/16 inch): usually normal. Mark, date, monitor.
- 1/8 to 1/4 inch: moderate. Monitor monthly. May need cosmetic repair to keep water out.
- Wider than 1/4 inch: structural concern. Get a structural engineer.
- Any horizontal crack: red flag for soil pressure on the wall. Engineer.
- Stair-step crack in brick or block: red flag for foundation movement. Engineer.
- Diagonal crack from a corner of a window or door: often points to settlement on one side. Engineer if growing.
- Crack that appeared suddenly or is actively growing: active movement. Engineer.
- Crack with water intrusion: waterproofing problem at minimum, possibly structural.
- Crack with sticking doors or windows on the same wall: foundation movement affecting framing. Engineer.
How to monitor a crack
- Mark each end of the crack with a small pencil tick on the wall.
- Write the date next to each mark.
- Photograph the crack with a ruler or coin in the frame for scale.
- Note the widest point (in millimeters or fractions of an inch).
- Re-check monthly. Compare photo to photo.
- If marks haven't moved over 6 to 12 months, the crack is stable.
- If marks have moved, the crack is growing. Time for a professional.
Crack monitors (small plastic devices that mount across the crack and show movement with a grid) cost $10 to $25 and give precise readings. Useful for cracks you're actively tracking.
Vertical vs horizontal vs diagonal
- Vertical cracks: most often from concrete shrinkage or minor settling. Usually the least concerning when small.
- Horizontal cracks: almost always a red flag. They indicate soil or water pressure pushing on the foundation wall from outside. Don't ignore.
- Diagonal cracks: often from one side of the foundation settling more than the other. Severity depends on size, location, and whether they're growing.
- Stair-step cracks (in masonry): follow the mortar lines between bricks or blocks. Strong indicator of foundation movement.
- Wide at top, narrow at bottom: upper section is moving.
- Wide at bottom, narrow at top: often heave from below.
Where cracks usually appear (and what they mean)
- Basement wall, vertical, near middle of a long wall: often shrinkage. Usually stable.
- Basement wall, horizontal, mid-height: soil pressure. Concerning.
- Above a window or door: framing settlement. Cosmetic if small.
- At a corner of a window or door: stress concentration. Watch growth.
- Slab floor, hairline: normal shrinkage.
- Slab floor, wider, with displacement (one side higher): heave or settlement. Engineer.
- Garage floor: commonly cracks; usually cosmetic if no displacement.
- At control joints (visible saw cuts in slabs): intentional. The joint is designed to crack there.
What changes the urgency
- Time of year: seasonal cracks open in dry summer, close in wet winter. Monitor over a full year before assuming a 1/8-inch crack is growing.
- Recent drought or flooding: soil moisture extremes move foundations.
- Nearby construction: excavation, heavy equipment, or new structures next door can shift soil.
- Tree growth: large trees within 20 feet of the foundation can pull moisture from soil and cause settlement.
- Plumbing leak underground: erodes soil under the foundation. Can cause sudden, alarming cracks.
- Earthquake or significant tremor: inspect after any event you felt.
What you can do before calling a pro
- Walk the exterior. Look for grade sloping toward the house, gutter overflow, downspouts dumping at the foundation.
- Check for visible water entry points.
- Document the crack with photos and measurements.
- Note any related symptoms (sticking doors, sloping floors, drywall cracks above).
- Check whether the home has had a foundation inspection in the past.
When to call a structural engineer (not just a foundation contractor)
Foundation contractors sell foundation repair. Their incentive is to find work. A structural engineer ($300 to $700 for a residential inspection) gives an independent assessment without the conflict of interest.
Call an engineer for:
- Any horizontal crack.
- Any crack wider than 1/4 inch.
- Any crack that's actively growing.
- Stair-step cracks in masonry.
- Cracks combined with sticking doors, sloping floors, or chimney separating from house.
- Before paying a foundation contractor for any major repair. Get the engineer's opinion first.
- Before buying a home with visible foundation cracks.
If repair is needed
- Cosmetic crack repair (epoxy or polyurethane injection): $300 to $1,500. Stops water entry, doesn't address structural cause.
- Carbon fiber straps: $500 to $1,500 per strap. Reinforce walls bowing inward.
- Wall anchors / helical tieback: $1,000 to $3,500 per anchor. For walls being pushed in by soil pressure.
- Piers (push or helical): $1,500 to $3,000 per pier, often multiple needed. For settled foundations.
- Full underpinning or wall rebuild: $20,000 to $100,000+.
Get multiple bids on major work. Bids from contractors who specialize in different methods can vary widely.
Common mistakes
- Patching a crack and assuming it's solved. Patching doesn't stop movement; it just hides what's happening underneath.
- Hiring a foundation contractor without an engineer's assessment first.
- Ignoring a horizontal crack because it's narrow.
- Not photographing before any repair. The pre-repair documentation is needed if the crack returns.
- Watering plants close to the foundation. Wet/dry cycles cause soil movement.
- Letting downspouts dump at the foundation. The single biggest controllable cause of foundation cracks.
Good maintenance rhythm
- Yearly: walk the foundation perimeter (inside and outside). Note any new cracks.
- Monthly: re-photograph any crack you're monitoring.
- Seasonally: check gutter and downspout drainage. Water near the foundation drives many crack problems.
- After significant rain, drought, or earthquake: inspect.
- After any nearby construction or tree removal: inspect for new cracks within a year.
- Before buying a home: have a structural engineer review any visible cracks.
- Keep a folder of dated photos and measurements for every monitored crack.