Spotting a crack in your foundation can feel like finding a mystery clue in your own home. Is it harmless? Is it a warning sign? And why did it show up now—right after that week of heavy rain, a deep freeze, or a big windstorm?
Foundation cracks are common, especially in climates where the ground expands and contracts through the seasons. Many cracks are minor and expected as a home settles. Others can point to shifting soil, drainage problems, or structural movement that deserves a closer look.
This guide will help you identify the most common types of foundation cracks, understand what causes them, and decide which ones you can monitor versus which ones should get professional attention. Along the way, we’ll also talk about how storms and yard conditions can quietly contribute to foundation stress—because what happens outside your house often shows up inside your basement.
Why foundations crack in the first place (and why it’s not always bad news)
Concrete is strong, but it’s not flexible. When the ground underneath a foundation shifts even slightly, concrete tends to relieve that stress by cracking. That sounds scary, but it’s also normal: many foundations develop small shrinkage cracks as concrete cures, and many homes experience minor settlement over time.
The key is learning to read the “story” the crack is telling. The direction, width, location, and whether it’s changing are all more important than the simple fact that a crack exists.
It also helps to remember that foundations don’t exist in isolation. Soil moisture, drainage, tree roots, and stormwater all influence what’s happening under and around your home. If you’ve recently had extreme weather, a rapid snowmelt, or a major storm, it’s smart to do a more careful check—even if your house has been fine for years.
A quick map of crack types: hairline, vertical, diagonal, horizontal, stair-step
Before getting into what’s “normal” versus “needs attention,” it helps to categorize what you’re seeing. Most foundation cracks fall into a few recognizable patterns.
Hairline cracks are extremely thin, often less than 1/16 inch. Vertical cracks run mostly up and down. Diagonal cracks cut across at an angle. Horizontal cracks run side-to-side and often raise the most concern. Stair-step cracks appear along mortar joints in block or brick foundations and look like a set of steps.
Each pattern tends to connect with different forces: shrinkage, settlement, lateral pressure, or uneven movement. You don’t need to be an engineer to make a first-pass assessment—but you do need to look closely and track changes.
Hairline cracks: when “normal settling” is actually normal
What hairline cracks usually mean
Hairline cracks are often the least concerning. Many appear within the first year or two after a home is built as concrete cures and the structure settles into place. They can show up in basement walls, slab floors, garage slabs, or at the corners of windows and doors.
If the crack is very thin, not widening, and not allowing moisture through, it’s often something you can monitor rather than rush to repair. That said, even “normal” cracks can become pathways for water if drainage is poor.
A good rule of thumb: if you can’t fit the edge of a coin into the crack and it hasn’t changed over time, it’s commonly considered low risk—especially if it’s vertical and not accompanied by other symptoms.
How to monitor them without overthinking it
Take a clear photo with a date stamp (or just keep a folder on your phone). Place a small reference object near the crack—like a ruler or coin—so you can compare later. If you want a simple DIY tracking method, you can mark the ends of the crack lightly with pencil and note the date beside it.
Check again after big seasonal transitions: spring thaw, long rainy periods, or deep winter cold snaps. Many cracks look “worse” when humidity changes or when the basement is drier than usual, so monitoring over time is more reliable than a one-time glance.
If you notice water staining, dampness, or a musty smell near even a small crack, treat that as a separate issue: moisture management. A hairline crack plus persistent moisture is no longer just cosmetic.
Vertical cracks: often manageable, sometimes a clue
Vertical cracks and typical settlement patterns
Vertical foundation cracks are commonly associated with normal settling. As the soil compresses under the weight of the home, the foundation can develop vertical or slightly diagonal cracks—especially near corners or where there are changes in wall height.
In poured concrete foundations, these cracks can be straightforward to seal if they’re letting in water. In block foundations, vertical cracking may follow mortar joints and can be a bit more complex, but still not automatically a structural emergency.
What matters most is whether the crack is stable. A stable vertical crack that’s been the same size for years is usually far less concerning than a newer crack that’s widening quickly.
When vertical cracks deserve more attention
If a vertical crack is wider than about 1/8 inch, if it’s growing, or if you can see displacement (one side of the crack is higher or pushed inward compared to the other), it’s time to take it more seriously.
Also watch for “paired symptoms” like sticking doors, new gaps around window frames, or sloping floors. A crack doesn’t always act alone—movement often shows up in multiple places.
If you’re unsure, a foundation specialist or structural engineer can help you understand whether you’re looking at simple shrinkage or an ongoing settlement problem that needs stabilization.
Diagonal cracks: the “uneven settlement” signal
Why diagonal cracks appear
Diagonal cracks often point to uneven settlement—meaning one part of the foundation is moving differently than another. This can happen when soil conditions vary under the house, when one area stays wetter than another, or when a corner is affected by drainage patterns.
In many homes, diagonal cracks show up near openings like windows and doors because those areas are naturally weaker points in a wall. You might also see diagonal cracks extending from the corners of basement windows.
A small diagonal crack that is stable may not be urgent, but it’s worth tracking carefully because it can indicate differential movement.
What to look for besides the crack itself
Check whether the crack is wider at one end than the other. A crack that tapers may indicate movement that has slowed or stopped, while a crack that is widening overall can suggest ongoing shifting.
Look at the outside of the foundation too. Sometimes diagonal cracking corresponds with grading issues, downspouts dumping water near one corner, or soil erosion that’s undermining support.
If the crack is accompanied by noticeable floor slope, gaps where walls meet ceilings, or repeated water intrusion, it’s a good idea to book an assessment rather than relying on DIY sealing alone.
Horizontal cracks: the pattern that usually needs a closer look
What causes horizontal foundation cracks
Horizontal cracks often form when there’s lateral pressure pushing in on the foundation wall. The most common source is soil pressure—especially when soil becomes saturated and heavy after prolonged rain or rapid snowmelt.
Clay-heavy soil is notorious for expanding when wet and shrinking when dry. That repeated cycle can press against foundation walls from the outside. Over time, the wall may bow inward slightly, and horizontal cracking can appear around mid-wall height.
Horizontal cracks are not always an immediate disaster, but they are one of the clearest signs that a wall is under stress. They deserve professional evaluation sooner rather than later.
Signs that a wall may be moving inward
Stand back and sight along the wall. If it looks wavy, bowed, or out of plane, that’s important. You can also use a long level or straightedge to see if there are obvious bulges.
Pay attention to whether the crack is accompanied by crumbling concrete, efflorescence (white powdery deposits), or water seepage. These clues suggest that the wall is not only cracking but also experiencing moisture movement.
If you see a horizontal crack plus bowing, don’t wait for it to “settle down.” Early reinforcement options are often less invasive than delayed repairs.
Stair-step cracks in block or brick: when mortar lines tell the tale
Why stair-step cracks happen
In concrete block or brick foundations, cracks often follow the mortar joints, creating a stair-step pattern. This can happen due to settlement, lateral pressure, or a combination of both.
Small stair-step cracks can be relatively common, especially in older homes. Mortar can weaken over time, and minor movement tends to show up along these joints.
That said, stair-step cracking can also be a sign that one section of the foundation is moving differently—especially if the crack is widening or if the blocks appear offset.
How to tell cosmetic from concerning
If the crack is thin, stable, and there’s no displacement, it may be something you monitor and seal for moisture control. But if the crack is widening, if you can see blocks shifting, or if the crack is paired with interior wall cracks upstairs, it’s time for a deeper look.
Also check the exterior brickwork (if you have it). Stair-step cracks in exterior brick can be related to foundation movement, but they can also come from issues with lintels, moisture, or thermal expansion. Context matters.
When in doubt, it’s worth having a professional assess whether the crack is simply aging mortar—or a sign of structural movement that needs stabilization.
Width, length, and displacement: the three details people miss
Most homeowners focus on the fact that a crack exists, but the more useful questions are: How wide is it? Is it getting wider? And is one side of the crack no longer aligned with the other?
Width is easy to estimate with a ruler or crack gauge. Length matters because longer cracks can indicate a larger stress pattern, though long hairline shrinkage cracks can still be benign. Displacement—where one side is higher, pushed in, or pulled out—is often the biggest red flag because it suggests structural movement, not just surface cracking.
As a practical guideline, cracks wider than 1/8 inch, cracks that are actively changing, and cracks with displacement should be evaluated. And any crack that’s letting in water consistently should be addressed for moisture control, even if it’s not structural.
Water changes everything: how moisture turns small cracks into recurring problems
Why water intrusion is more than a nuisance
Water entering through a crack can lead to mold, damaged finishes, and that persistent basement smell nobody wants. But it can also accelerate deterioration. Freeze-thaw cycles can widen cracks as water expands when it freezes, and repeated wetting can weaken concrete and mortar over time.
Even if a crack is “normal,” water moving through it is a sign that the outside conditions—grading, downspouts, drainage—aren’t doing their job. Sealing the crack from the inside can help, but it’s rarely the whole solution.
A dry foundation is easier to evaluate, easier to maintain, and far less likely to develop secondary issues. Moisture control is one of the best investments you can make in long-term foundation health.
Simple drainage checks that make a big difference
Start with gutters and downspouts. Make sure gutters are clean and downspouts discharge well away from the foundation (often 6 feet or more, depending on your property). Look for low spots near the house where water pools after rain.
Check grading: the ground should slope away from the foundation so water naturally runs outward, not inward. If you have garden beds piled high against the house, that can trap moisture against the foundation wall.
Finally, pay attention to sump pump performance (if you have one). A sump pump that’s cycling constantly or failing during storms can contribute to repeated wetting around the foundation.
Storms, trees, and foundation cracks: the outdoor connection homeowners overlook
How storms can set off a chain reaction
Big storms don’t just bring wind—they bring saturated soil, sudden runoff, and sometimes damage to the landscape that changes how water flows. When soil becomes waterlogged, it presses harder against foundation walls. When water drains unevenly, it can wash out soil in one area and leave another area swollen and heavy.
Storms can also damage trees, leading to leaning trunks, broken limbs, or uprooted root plates that disturb the soil around your home. That soil disturbance can alter drainage paths or create voids that contribute to settlement.
If you’ve had a major storm and you’re noticing new cracks (or old cracks suddenly leaking), it’s smart to inspect both your foundation and your yard. The “cause” might be outside.
When tree damage becomes a foundation issue
Trees can affect foundations in a few ways: roots can draw moisture from soil (causing shrinkage in clay soils), heavy canopies can alter how rain hits the ground, and storm-damaged trees can physically disrupt soil when they shift or fall.
After severe weather, some homeowners need help fast to clear hazards and prevent further damage. If a tree has fallen, is hanging over the home, or is threatening utility lines, getting emergency tree services after storms can be part of protecting the structure—not just the yard.
Even if the immediate danger is handled, it’s worth reassessing drainage afterward. A removed tree can change shade and evaporation patterns, and an uprooted root system can leave uneven ground that directs water toward the foundation.
Cracks in different parts of the house: basement walls vs slab vs garage
Basement wall cracks: common, but context matters
Basement walls are constantly resisting soil pressure, so cracking patterns here are especially informative. Vertical cracks may be settlement or shrinkage; horizontal cracks may indicate lateral pressure; stair-step cracks in block may suggest movement along joints.
Because basement walls are below grade, water intrusion is also more likely. Even a small crack can become a leak during heavy rain. If you see dampness, efflorescence, or peeling paint near a crack, treat it as a moisture management issue as well as a structural question.
Also check for bowing, especially in older homes or homes with clay soil. Bowing plus horizontal cracking should be assessed promptly.
Slab and garage floor cracks: often cosmetic, sometimes settlement
Cracks in slabs and garage floors are extremely common. Many are shrinkage cracks that form as concrete cures. These often look like thin lines that wander across the floor.
Where you want to pay closer attention is when a slab crack shows vertical displacement (one side higher than the other), or when the crack is paired with a noticeable dip or heave. That can indicate soil movement or poor compaction beneath the slab.
Garage floors also take a beating from vehicles, road salt, and temperature swings. Some cracking is expected, but water pooling near a crack or a crack that’s widening may signal drainage issues outside the garage door or along the driveway edge.
DIY sealing vs professional evaluation: knowing what each can (and can’t) do
What DIY fixes are good for
DIY crack sealants can be helpful for minor, stable cracks—especially to reduce moisture intrusion or drafts. For example, epoxy or polyurethane injection kits can work well for certain vertical cracks in poured concrete when the underlying issue is stable.
Caulks and patching compounds can improve appearance, but they’re not structural repairs. If the foundation is moving, surface patches tend to crack again because they’re not addressing the cause.
DIY is best when you’ve confirmed the crack is stable, you’ve improved drainage, and you’re trying to keep the space dry and comfortable.
When it’s worth bringing in an expert
If a crack is horizontal, widening, shows displacement, or is paired with bowing walls or interior symptoms (sticking doors, sloping floors), professional assessment is the safer path.
A qualified foundation contractor can evaluate drainage, soil pressure, and structural movement, and recommend reinforcement, waterproofing, or stabilization options. In some cases, a structural engineer’s report can help you understand the severity and choose the right repair approach.
It’s also worth calling a pro when you feel uncertain. The goal isn’t to panic—it’s to avoid guessing wrong when the fix could be simple now and expensive later.
How to document cracks for peace of mind (and for future resale)
Keeping a simple crack log can take a lot of stress out of homeownership. When you can see that a crack hasn’t changed in 18 months, it’s easier to stop worrying about it every time you walk past.
Create a folder with photos, dates, and notes about weather events (heavy rain, freeze-thaw weeks, major storms). If you measure crack width, write it down. If you seal a crack, note the product and date.
This documentation can also be helpful if you ever sell your home. Being able to show that you monitored and maintained the foundation responsibly can build buyer confidence and reduce last-minute surprises during inspection.
Yard projects that can accidentally worsen foundation cracking
Changing drainage without realizing it
Small landscaping changes can have big effects on where water goes. Adding a garden bed, installing edging, or building a walkway can unintentionally create a low spot that funnels water toward the foundation.
Even adding soil against the house can be risky if it brings grade too high or covers weep holes (in some foundation types). The goal is always to keep water moving away from the home.
If you’re doing a yard project, do a “rain test” afterward: the next time it rains, walk around and see where water flows and where it pools.
Removing trees and stumps the right way
When a tree is removed—especially after storm damage—homeowners sometimes leave the stump or try to dig it out. But stumps and major roots can be stubborn, and aggressive digging near the home can disturb soil that supports foundation areas or changes drainage patterns.
In many cases, using professional stump removals helps you avoid unnecessary excavation and reduces the chance of leaving a void that later settles. It’s also a cleaner way to restore the grade so you can manage runoff properly.
After stump removal, consider topping up and compacting soil appropriately and rechecking that water still slopes away from the house. The “after” part is just as important as the removal itself.
When storm cleanup intersects with home protection
After a major weather event, it’s easy to focus on what’s visible—fallen branches, damaged fences, scattered debris. But a smart storm recovery plan also includes checking the less obvious risks: downspouts knocked loose, gutters clogged with leaves, and soil washed away near the foundation.
If you’re coordinating tree work after a storm, it can help to work with a team that understands both safety and property protection. If you need to schedule an assessment or ongoing maintenance, you can contact Wise Owl Tree to talk through options for addressing storm-damaged trees and reducing future risk around the home.
Once the immediate hazards are handled, do a full perimeter walk: look for new low spots, exposed roots, or areas where water now channels differently. Those changes can be the hidden reason a “new” foundation crack appears weeks later.
Red flags that mean “don’t wait and see”
Structural movement signs inside the home
Foundation issues often show up in the living spaces too. Watch for doors that suddenly stick, windows that don’t open smoothly, or new gaps at the top of door frames. Drywall cracks that reappear after being repaired can also be a clue.
Floors that slope noticeably or feel bouncy in a new way can indicate shifting support. If multiple symptoms show up around the same time as foundation cracking, it’s a sign that movement may be active.
These symptoms don’t automatically mean the house is unsafe, but they do mean you should stop guessing and get a professional evaluation.
Foundation wall distress signs in the basement
Horizontal cracks, bowing walls, and significant displacement are top-tier warning signs. So are cracks that are rapidly widening or cracks paired with recurring water intrusion.
Another subtle clue is a wall that looks “sheared,” where the top portion appears shifted relative to the bottom. If you see this, take photos and call a professional promptly.
Finally, if you notice cracking that’s accompanied by a sudden increase in humidity, mold growth, or persistent dampness, address moisture immediately while investigating the underlying cause.
Normal vs needs attention: a practical cheat sheet you can use today
If you want a simple way to think about it, here’s a homeowner-friendly framework. Cracks that are thin, vertical, and stable—especially in newer concrete—are often normal settling or shrinkage. Cracks that are hairline and dry are usually monitor-and-maintain territory.
Cracks that are widening, letting in water regularly, or showing displacement deserve attention. Diagonal and stair-step cracks often fall in the middle: sometimes they’re stable, sometimes they’re the first sign of uneven settlement.
Horizontal cracks and bowing walls are the ones to treat as higher priority. They’re often tied to soil pressure and can worsen if drainage and reinforcement aren’t addressed.
Putting it all together after the next big weather swing
Foundation cracks are one of those homeownership realities that get less scary the more you understand them. The goal isn’t to aim for a crack-free foundation forever—it’s to recognize which cracks are typical, which ones are changing, and what outside conditions might be contributing.
After heavy rain, a spring thaw, or a major storm, take 20 minutes to do a quick check: gutters and downspouts, grading near the home, basement walls, and any known cracks you’re tracking. A little consistency goes a long way.
And if you ever feel stuck between “this is probably fine” and “this might be serious,” you’re not alone. Getting the right eyes on it—whether that’s a foundation professional for structural questions or a tree and drainage expert for yard-related causes—can save you money and stress over time.