You find a crack in the concrete along the bottom of the house. Maybe it runs straight up the stem wall from the footing. Maybe it runs sideways along a garage wall that has dirt piled against the other side. Someone online says vertical cracks are fine and horizontal ones are bad. That rule is half right, and half right is a risky thing to lean on.
Direction is a useful first clue. It narrows the list of things that could have caused a crack. It doesn’t name the cause, and it doesn’t tell you whether the crack is still moving. This post walks through what crack direction is associated with in each part of a foundation, using concrete-industry and federal housing references, so you can describe what you see clearly and know which cracks to get looked at. For the broader picture, start with our foundation cracks guide. For repair options once a cause is known, see foundation crack repair.
In short: vertical and diagonal cracks in foundation concrete are often linked to shrinkage, but taper, offset, and growth can point to settlement or heave. Horizontal cracks in walls that hold back soil are more often linked to sideways load and deserve a professional look sooner.
Why concrete cracks in a direction at all
Concrete shrinks as it dries. On its own that wouldn’t crack anything. The American Concrete Institute’s crack report puts it plainly: “If the shrinkage of concrete could take place without restraint, the concrete would not crack. It is the combination of shrinkage and restraint (provided by another part of the structure, by the subgrade, or by the moist interior of the concrete itself) that causes tensile stresses to develop” (ACI 224.1R-07).
A foundation wall is held at its base by the footing and the soil. When it tries to shorten, something has to give, and the industry notes below describe those shrinkage cracks as mostly vertical to diagonal. Loads work differently. “Load-induced tensile stresses result in cracks in concrete members,” the same report notes. A wall pushed sideways by soil gets bent, and HUD’s guide ties horizontal cracking in foundation walls to exactly that.
So direction hints at which kind of force was involved. It’s a tendency, not a rule, and most of this post is about the exceptions.
Vertical cracks
What they’re usually associated with
The Concrete Foundations Association’s tech note on wall cracking says “shrinkage and temperature cracks are most often vertical to diagonal” and “typically emanate from a corner of a window, beam pocket, or other opening.” HUD’s Residential Rehabilitation Inspection Guide describes a related pattern: cracking at corners or openings in concrete foundations “due to drying shrinkage of concrete walls that are prevented from contracting,” which “will occur early in the life of the building.”
FEMA’s homeowner-level seismic assessment guide adds a calm baseline: “Cracks in foundation elements are not uncommon and can occur simply from normal shrinkage of concrete” (FEMA P-50).
So a fairly uniform vertical crack in a stem wall, one that has been there for years, doesn’t line up with anything else, and isn’t letting water in, often fits the shrinkage story. Builders even plan for it. “Control joints are intentional weak spots designed to induce shrinkage or thermal cracks in pre-determined locations,” the CFA note explains. A straight, tooled line in the concrete may be a joint doing its job.
When a vertical crack matters more
Three details change the reading.
- Taper. “Vertical cracks which are significantly wider at the top or bottom could indicate heaving or settlement,” according to the CFA note. HUD says settlement produces “cracks that taper, being largest at one end and diminishing to a hairline at the other, depending on the direction and location of settlement below the wall.” Which way it tapers is something to record, not something to diagnose from.
- Offset. If one side of the crack sits higher or farther out than the other, the two pieces have moved relative to each other. ACI’s evaluation guidance says “any displacement of the surface (change in elevation) across the crack should also be documented.”
- Location at an add-on. HUD flags “tapering cracks, or cracks that are nearly vertical and whose edges do not line up” at the joints of “projecting bay windows, porches, and additions,” and says these “indicate differential settlement due to inadequate foundations or piers under the projecting element.” If your house has an addition or an enclosed porch, the seam where it meets the original foundation is a good place to look closely.
A vertical crack that keeps going, from the stem wall into the slab, the framing, or the drywall above, is also telling you more than one that stops at the concrete. HUD notes that settlement cracks “may extend through contiguous building elements such as floor slabs, masonry walls above the foundation, and interior plaster work.”
Diagonal cracks
Diagonal cracks sit between the two. Many start at the corner of an opening, a pattern the CFA note calls reentrant cracking and groups with shrinkage. HUD groups diagonal, tapering cracks with settlement, and warns that “many signs of masonry distress are incorrectly diagnosed as settlement-related when in fact they are due to moisture and thermal movements.”
Both can be true on the same house. The tie-breakers are the same as for vertical cracks: taper, offset, change over time, and what else is happening nearby (a door that started sticking, a floor that slopes toward that corner). Our posts on sticking doors and windows and seasonal vs progressive cracks cover those companion clues.
Horizontal cracks
In walls that hold back soil
This is where the “horizontal is bad” rule comes from, and here it carries real weight. “Cracks which are horizontal are most likely caused by an applied load,” the CFA note says. HUD, writing about brick and block foundation walls, is more direct: horizontal cracking “is potentially serious as it indicates that the vertical supporting member (the foundation wall) that is carrying a portion of the structure above is ‘bent’ or ‘broken.’”
HUD lists causes such as improper backfilling, vibration from heavy equipment or vehicles close to the wall, and swelling of water-saturated soils next to it. When expansive soil is suspected, it says to “examine the exterior for sources of water such as broken leaders or poor surface drainage.”
The California Residential Code treats sideways soil pressure as a design load. Its masonry foundation-wall tables are organized by soil class and lateral soil load, and it requires walls to be “designed in accordance with accepted engineering practice” where they are subject to hydrostatic pressure from groundwater, or hold back more than 48 inches of unbalanced backfill without permanent lateral support at the top or bottom (CRC R404.1.1). The CFA note adds that “typical basement walls are not designed to act as retaining walls” until they are secured at the top and bottom.
On La Jolla hillside lots, walls that hold back soil can include a garage cut into a slope, a lower-level room, or a stepped foundation where grade changes along the house. A horizontal crack there, especially with any bow, lean, or water, is a reason to call rather than wait. Freestanding retaining walls in the yard have their own checklist; see retaining wall repair and our post on leaning retaining wall causes.
In short stem walls and at the footing line
Not every horizontal line is a bending crack. A short stem wall with roughly the same soil level on both sides isn’t holding back much soil, which puts it in a different situation from the walls R404.1.1 singles out. A horizontal line where the stem wall meets the footing can be a construction joint from a separate pour that has always looked that way. Our footing damage post covers how to tell an old joint from a new separation.
What changes the picture is the same list as before: the line is new, it’s wider than it was, the wall above has moved outward or inward, or there’s soil or water coming through.
In slabs
Slab cracks don’t fit neatly into horizontal or vertical, since the slab is flat. HUD’s guide offers a related clue about position: interior slab cracking “is usually due to shrinkage or minor settlement below the slab,” but “if cracking is near and parallel to foundation walls, it may have been caused by the movement of the walls or footers.” A slab crack that tracks the perimeter, especially with one side higher, points attention to the foundation edge. Our slab foundation repair page covers slab-specific evaluation.
Piers and posts
Under raised floors, piers carry interior loads. HUD’s guide, writing about masonry piers, notes that “a sign of overstressing of piers is vertical cracking or bulging,” and that piers “often settle differentially.” A pier with a vertical split, a tilt, or a gap between the post and the beam above is worth photographing and mentioning during any foundation inspection.
A quick reference
| Direction and place | Often associated with | What raises concern |
|---|---|---|
| Vertical, uniform, stem wall | Drying shrinkage under restraint | Taper, offset, water, growth, continues into framing |
| Vertical or diagonal from a corner or opening | Shrinkage concentrated at the corner | Taper, offset, companion symptoms nearby |
| Near-vertical at an addition or porch | Differential settlement of the add-on (HUD) | Edges don’t line up; gap widening |
| Horizontal, wall holding back soil | Sideways soil load (bending) | Bow, lean, water or soil coming through |
| Horizontal at stem-to-footing line | Can be a construction joint | New separation, movement, daylight |
| Slab crack parallel to a foundation wall | Movement of the wall or footing (HUD) | Vertical step across the crack |
| Vertical split in a pier | Overstressing (HUD) | Tilt, bulge, loss of bearing |
These are associations from published references, not a diagnosis. As ACI’s report says, “the cause of the cracking should be established before repairs are specified.”
What direction can’t tell you
Direction doesn’t tell you whether a crack is active. HUD notes that “a clean crack indicates recent movement; a dirty or previously filled crack may be inactive,” but even that is a hint, not a test. It doesn’t tell you how deep the crack goes, whether reinforcement inside has corroded, or what the soil is doing. And it doesn’t override context. FEMA P-50 notes that when “cracking becomes extensive and differential settlement is significant,” the movement “is likely associated with soil deformations,” including clay soils that shrink and swell, fill that compresses, and slopes that creep.
That’s also why sealing a crack before anyone understands it can backfire. Injection resins have different jobs (our post on epoxy vs polyurethane crack injection explains them), and a filled crack can hide whether movement continues.
For crack vocabulary, see our hairline vs structural foundation cracks post. For brick, block, and stucco walls above the foundation, see stair-step and horizontal wall crack patterns. This post stays with the concrete below.
What to do with what you see
- Write down direction, place, and length. Note which wall, how far from a corner, and whether the crack starts at an opening or a joint.
- Look for taper and offset. Is it wider at one end? Does one side sit higher or proud of the other?
- Check whether it continues. Look above and beside it: slab, sill, drywall, door frames.
- Note water and soil. Dampness, staining, or soil coming through the crack matter, especially in walls that hold back soil.
- Start a record. A dated photo and a simple gauge reading turn “I think it’s bigger” into evidence. Our companion post on crack monitoring with telltales and photos shows how.
Call sooner, without waiting for a record, if a wall that holds back soil has a horizontal crack with any bowing or lean, if a crack has a visible step across it, or if cracks show up together with doors that suddenly bind or floors that start to slope.
Cost factors, not prices
We don’t publish prices. What shapes the scope after a crack is evaluated: whether the cause is shrinkage, settlement, heave, or lateral soil load; whether the crack is active or dormant; whether the wall holds back soil; access (crawl space height, finished interior surfaces, landscaping or hardscape against the wall); drainage or plumbing problems that need fixing first; whether engineering or a soils report is needed; and permit requirements. Our post on what drives foundation repair cost goes further.
Where we fit
We look at foundation cracks on site across La Jolla, map them against the rest of the house, and explain what we’re seeing before recommending anything. When a wall needs engineered design or a soils question needs answering, we coordinate with licensed engineers as needed; our structural engineer page explains how that works. This post is general education, not an engineering opinion about any specific house.
Next step
If you have a horizontal crack in a wall that holds back soil, a crack with a step across it, or a crack that’s growing, request a Free Quote for an on-site evaluation anywhere in La Jolla, or call (650) 739-6537.
Sources (accessed October 18, 2026)
- American Concrete Institute Committee 224, ACI 224.1R-07, Causes, Evaluation, and Repair of Cracks in Concrete Structures (2007), Sections 1.3.1, 1.3.9, 2.1, 2.2.1
- U.S. Department of Housing and Urban Development, Residential Rehabilitation Inspection Guide (2000), Sections 4.3, 4.4, 4.9
- Concrete Foundations Association, Tech Notes CFA-TN-004, Cracking in Concrete Walls
- 2025 California Residential Code, Sections R404.1.1 and R404.1.2.1
- FEMA P-50, Simplified Seismic Assessment of Detached, Single-Family, Wood-Frame Dwellings (May 2012), Section 5.3