Types of Foundation Cracks

Not all foundation cracks are created equal. Some are relatively harmless, cosmetic signs of normal settling. Others point to more serious movement, shifting soil, or water-related stress that needs attention sooner rather than later. 

At Bramwell-McKay Property Services & Consultants, we’ve spent nearly four decades helping homeowners tell the difference. We don’t just fix the cracks. We also explain what’s causing them, what to expect if they’re left unaddressed, and what the right path forward looks like.

If you’re seeing cracks in or around your foundation, here’s what you need to know.

What Causes Basement Foundation Cracks?

Before jumping into types, it helps to understand the forces at play. Foundation cracks usually appear as a result of movement, whether it’s from soil settling, water pressure, freeze-thaw cycles, or even poor construction practices.

In the U.S., our climate plays a major role. Wet seasons followed by long dry spells cause the soil around your foundation to expand and contract. This constant shift puts stress on the foundation walls and can eventually lead to cracking. Poor drainage, improper grading, tree roots, or construction on unstable soil can speed up the process.

The type, size, direction, and location of a crack will often reveal what kind of pressure caused it, and how urgent the issue is.

Should You Worry About Foundation Cracks — When to Call for Foundation Repairs

Seeing cracks in your foundation can be unsettling. Whether they appear as small hairlines in the basement wall or wide diagonal splits in your brick exterior, it’s natural to wonder how serious the damage might be and what it means for your home’s structural integrity.

A common misconception is that small cracks are nothing to worry about. While that’s sometimes true, even minor cracks can signal bigger problems, depending on where they show up and how they behave over time.

Here are a few warning signs that a foundation crack may need a professional evaluation:

• Cracks that are wider than 1/8 inch
• Cracks that change direction, grow over time, or allow water to seep through
• Cracks accompanied by bowing walls, uneven floors, or sticking doors and windows
• Cracks that run through bricks, not just mortar joints

The key is not to panic. But you also can’t ignore these red flags either. If you’re unsure what you’re looking at, that’s when it’s time to bring in an expert.

Not All Cracks Are Equal: Six Types of House Foundation Cracks

Knowing the different kinds of cracks and concrete foundation damage you may experience is the first step toward protecting your home’s structural integrity and your peace of mind. Here are a few cracks you may encounter in your home.

Vertical Foundation Cracks

Vertical cracks are some of the most common types of foundation cracks. They often appear as thin lines running straight up and down or slightly diagonal, typically in poured concrete walls.

In many cases, vertical cracks are often called settlement cracks because they are caused by normal settling that occurs as the house adjusts to its footing. These are usually cosmetic and can be sealed with epoxy or polyurethane to prevent moisture intrusion.

However, if the crack is widening, leaking water, or appears in conjunction with other symptoms (like mold or mildew), it could be a sign of hydrostatic pressure building up behind the wall—especially if your drainage system isn’t working properly.

Horizontal Cracks

Horizontal foundation cracks are more serious. These tend to appear in block foundations and usually indicate pressure from the outside. The source is most often saturated soil pushing against the basement wall. This kind of crack often shows up midway down the wall and may be accompanied by bowing or inward movement.

Horizontal cracks are not something to wait on. They suggest structural instability and can lead to wall failure if left untreated. In many cases, reinforcement or wall anchoring will be required to stop the movement and prevent further damage. If you’re seeing a long, horizontal crack, particularly in combination with water issues, call a specialist immediately.

Stair-Step Cracks

These cracks follow the mortar joints in a zigzag pattern through concrete block or brick walls. Stair-step cracks are often a sign of uneven settling, where one part of the foundation is sinking faster than another. This could be caused by soil erosion, poor compaction, or water washing away the supporting soil under the footing.

Depending on their size and whether they continue to grow, stair-step cracks can range from cosmetic to severe. If you notice cracks like this near corners or on exterior walls, it’s time for a full evaluation to determine if foundation stabilization or underpinning is needed.

Diagonal Cracks

Diagonal cracks typically appear at a 30–75 degree angle and are often the result of differential settling. These may start at the corners of windows or doors and extend down toward the floor or out toward the ceiling. They’re especially common in poured concrete walls, but can also be seen in brick veneers.

Diagonal foundation cracks may be less alarming than horizontal ones, but still shouldn’t be ignored. The slope and direction of the crack can help determine where the pressure is coming from and how to address it before it spreads.

Hairline Cracks

Hairline cracks are extremely thin and often appear in new foundations as the concrete cures. While they may look harmless, they can allow water or radon gas to enter the basement if not properly sealed. 

Hairline cracks in dry, stable conditions may not need structural repair, but should still be monitored and sealed to avoid future problems. If you see multiple hairline cracks or if they’re appearing in combination with other warning signs (like musty smells or visible moisture), they could be symptoms of a bigger issue forming.

Cracks in Slab Foundations

Homes built on concrete slabs can experience cracks through the floor, especially if the underlying soil isn’t properly compacted or if there are moisture fluctuations. While hairline cracks in a slab are often normal, wider cracks or cracks that allow one side of the slab to lift or sink could indicate settling or heaving.

Slab cracks can be trickier to evaluate, so it’s worth having them looked at—especially if you’re noticing uneven flooring or separation along interior walls.

What Should You Do If You Find Foundation Cracks?

The most important step is to avoid making assumptions. Cracks don’t fix themselves—and what looks like a minor cosmetic flaw could be a sign of serious structural movement. On the other hand, not every crack requires expensive repairs. 

That’s why it’s so important to get a proper inspection from a qualified structural specialist, not just a general contractor.

At Bramwell-McKay, we believe in giving homeowners the full picture. We don’t push repairs you don’t need. We assess the cracks, evaluate the conditions around your home, and explain what’s happening in a way that makes sense. If it’s minor, we’ll tell you. If it needs attention, we’ll walk you through your options and help you make the best decision for your home and your future.

Get Foundation Crack Repair You Can Trust

Foundation cracks don’t have to be scary. But, they do need to be taken seriously. If you’ve spotted cracks in your basement, exterior brickwork, or slab, now’s the time to take the first step.

Schedule a consultation with Bramwell-McKay today, and let’s figure out exactly what your home is telling you so you can protect its value and stability for many years to come.