Acceptable Crack Width in Buildings: What’s Safe and When to Worry
When it comes to acceptable crack width, the maximum size of a crack in a building structure that doesn’t indicate a serious safety risk. Also known as non-structural cracking, it’s a normal part of how materials like concrete and brick settle over time. Most homes develop small cracks—especially in the first few years after construction. But not all cracks are the same. A hairline crack under 1mm wide is usually nothing to lose sleep over. Once you hit 2mm to 5mm, it’s time to pay attention. And anything wider than 5mm? That’s a red flag.
Foundation movement, the shifting of a building’s base due to soil conditions, water exposure, or poor construction. Also known as settlement, it’s the main reason cracks appear in walls and floors. This isn’t always bad. Many homes settle slightly after being built, especially if the ground wasn’t fully compacted. But if that movement is uneven—say, one side of the house sinks more than the other—you’ll see diagonal cracks near windows, doors, or corners. That’s where structural cracks, cracks that go beyond surface damage and affect load-bearing parts of the building. Also known as critical cracks, they can compromise the entire structure. These often run vertically or diagonally, are wider than 5mm, and may be accompanied by sticking doors, uneven floors, or gaps between walls and ceilings.
Cracks in plaster or drywall? Often just surface-level. But cracks in brickwork, concrete slabs, or load-bearing beams? That’s different. If you’ve seen a crack grow over a few months—or if water starts seeping through it—you’re dealing with something deeper. Soil type matters too. Clay soil expands when wet and shrinks when dry, which can push foundations around. Poor drainage, tree roots, or even nearby construction can make it worse.
You don’t need to panic over every line you spot. But you do need to know the difference between a cosmetic issue and a structural one. The acceptable crack width rule of thumb? Under 1mm? Monitor it. 1–5mm? Get it checked. Over 5mm? Don’t wait. Call a professional. Most people wait too long because they think cracks are normal—and they are, up to a point. But ignoring the wrong one can turn a small repair into a full foundation replacement.
What you’ll find in the posts below are real-world examples of cracks people have seen in their homes, what they meant, and what was done about them. From tiny hairline splits in bathroom tiles to major splits in basement walls, these stories show exactly how to read the signs—and when to act before it’s too late.
Foundation Crack Size: What’s Actually Safe?
Not every crack in your foundation spells disaster. This article explains how big a foundation crack can get before you really need to worry, what types of cracks to watch out for, and the quick tricks you can use to tell harmless from harmful ones. Get smart tips for tracking crack growth and see when it’s time to get a pro involved. Save yourself the stress (and the bill) by knowing what’s normal. It’s everything homeowners wish they knew about foundation cracks.
