Foundation Wall Cracks, Part 3: Cracks That Warrant Immediate Attention
In the first two parts of this series, we covered cracks that were mostly cosmetic and others that might need attention under certain circumstances.
Now, we’re looking at the ones that deserve your full attention — the cracks that can indicate active foundation movement.
These are the ones that can affect your home’s stability, safety, and long-term value if left unaddressed. But don’t worry — recognizing them early makes all the difference.
We’ll break this into two categories:
Inward movement (deflection)
Downward movement (settlement)
There’s a big difference between the two.
Inward Movement (Deflection)
If you have an unfinished basement with block (CMU) walls, you may have noticed one or more walls with a horizontal crack, possibly with additional cracks above or below it. At the ends of that horizontal crack, you might see zigzagging “stair-step” cracks.
If so, that’s clear evidence of wall deflection — inward movement.
Why Does the Wall Crack This Way?
Mortar joints in block walls are softer and weaker than the concrete blocks themselves. When lateral pressure builds, those joints are the first to give.
Here’s how wall failure tends to progress through its stages:
Stage 1: A horizontal crack forms across most of the wall (unless soil slopes dramatically outside).
Stage 2: Stair-step cracks appear at either end of the horizontal crack.
Stage 3: Shearing occurs — one or more rows of block begin sliding inward along the mortar joint, often near the floor. If you run your hand along the joint, you’ll feel a small “lip.”
Stage 4: Continued inward movement can eventually lead to partial or total wall collapse — rare, but extremely dangerous and costly (I’ve come across these situations a few times).
Common Causes of Deflection
Let’s look at what’s pushing on those walls:
Water Weight
When it rains, water fills the tiny voids between soil particles, dramatically increasing the soil’s weight and pressure against the wall. Think of it like filling a jar of gravel with water — the same sized jar suddenly gets much heavier.
Frost
If wet soil freezes, the water inside expands. This frost heave can push hard enough to crack mortar joints.
If the horizontal crack runs just above the frost line, frost is likely a factor.
Expansive Soils
Here in Central Virginia, we have no shortage of clay — bright red, messy, and highly reactive. When wet, it expands like a sponge and can apply pressure similar to frost but potentially across the entire wall height.
While block walls are more prone to bowing inward, poured concrete walls can experience the same forces. Instead of bowing, they tend to lean inward as one solid unit.
If you notice diagonal cracks near the top corners at either end of a poured wall, it’s a strong indicator of inward lean.
Downward Movement (Settlement)
“Every house settles.” We’ve all heard it. Yes, footer settlement is common, but that doesn’t mean it is benign and doesn’t need attention.
A broken arm is extremely common, but you still want to have that compound fracture fixed by a professional. I encourage you to investigate those settlement cracks and make sure it isn’t an active problem. Let’s take a look at the symptoms of footer settlement.
Signs of Foundation Settlement
Stair-Step Cracks in Walls
Settlement cracks almost always show up as stair-step patterns, often running from the top of the wall down to the footer — and you’re not likely to see them on less than two walls.
Why? Because when one corner of a home drops, it pulls two adjacent walls with it. The pattern often looks like a triangular wedge.
Occasionally, cracks appear on opposite sides of the house — usually when one entire section of the structure has settled more or less evenly, although it’s more likely you’ll see cracks on at least 3 walls if this is the case.
Doors and Windows That Stick or Misalign
When a portion of the foundation drops, the walls above follow. That movement can pull windows and doors out of square, making them difficult to open or close.
Drywall may also crack diagonally above corners of windows and doors in affected areas.
Cracks in the Basement Floor
Most homes are built with what’s called a three-piece foundation: the footer, the wall, and the slab floor. The floor sits on top of the footer. If the footer settles, it drags the wall (and sometimes the floor) with it.
In a corner that’s sinking, you might see a crack connecting one wall to another, breaking the floor into a triangle shape.
That said, not all floor cracks mean settlement — many slabs crack as they cure, so don’t panic unless you see other symptoms too.
Causes of Foundation Settlement
Expansive Soils
Once again, clay takes center stage. It swells when wet and shrinks when dry, causing constant stress beneath your footers.
Anything above the frost line can also shift with freeze/thaw cycles.
Shallow footers amplify the problem — the deeper the footer, the more stable the bearing soil.
Slope and Runoff
Homes built on slopes (especially with walkout basements) can experience soil erosion on the downhill side. Over time, water runoff removes the supporting soil around the footer, leading to uneven settlement.
Saturated Soil
Even with footers below the frost line, excess moisture can soften the bearing soil.
Saturated soil loses its ability to hold weight, allowing sections of the footer to sink or rotate. When you step into mud, you sink. Homes do the same thing, just with much more weight.
In poured concrete walls, settlement often presents as long slanted or diagonal cracks that extend from top to bottom — roughly mirroring the stair-step pattern you’d see in block walls.
What Should I Do About This?
If you’ve read this far and some of these descriptions sound familiar — don’t panic.
There are reliable, long-term repair solutions for both inward and downward foundation movement.
When I worked for a foundation repair company, there were very few walls we couldn’t stabilize and prevent from becoming a safety hazard.
I’ll cover repair methods for inward and downward movement in another series, but for now, the most important step is to get an expert opinion.
If you’re unsure, call in a professional to assess the exact cause and severity of movement before it progresses.
Key Takeaway
Everyone deserves to feel safe in their own home. If you’re losing sleep over cracks or movement and can’t tell whether it’s serious, let me take a crack at it. 😉
If you’re in Central Virginia, schedule a foundation inspection with Integrity Foundation Inspections. I’ll give you an honest assessment of whether your home needs attention — no gimmicks, no scare tactics, just facts.
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