Is it Normal for a 100 Year Old House to Have Cracks?

If you live in a house built a century ago, you’ve probably spotted cracks along the walls or ceiling. Are they a cause for panic? Most of the time, they’re just part of the deal.

A 100-year-old home has been through a lot. Weather changes, settling foundations, and even the materials used back then all play a part. Builders a hundred years ago didn’t have today’s tech, so plaster, mortar, and old timber behave differently than modern drywall and concrete. Cracks can pop up as seasons come and go, as wood dries out further, or as bricks shift just a hair more after decades.

Sometimes these cracks are just cosmetic—a reminder your house is real, not a TikTok-perfect model home. But ignoring certain cracks can backfire, especially if they’re getting bigger or showing up in weird places. So how do you tell what’s normal and what’s not? Let’s get into it, crack by crack, so you know exactly what’s going on in your old walls—and what to do about it.

• Why Old Houses Crack
• Types of Cracks You’ll See
• When to Worry About Cracks
• How to Monitor Cracks
• Repair Tips and Prevention

Why Old Houses Crack

Cracks in a 100 year old house are practically expected. Let’s get down to why these cracks show up in the first place.

First, it’s the materials. Builders a century ago used lime-based mortar, solid brick, and horsehair plaster, which all age differently than today's drywall and concrete. Over time, these materials dry out, shrink, and sometimes expand. Add in years of vibration from traffic, nearby construction, or even minor earthquakes, and you get tiny gaps.

Another big reason: settling. A house this old has had years to shift bit by bit. Then you’ve got weather. Freeze-thaw cycles, humidity changes, and heavy rain cause bricks and timber to expand and contract. In the U.S., homes older than 75 years often have noticeable cracks just from these temperature swings. Even a stat from the National Association of Home Builders says that about 60% of homes over 80 years old display visible crack patterns, mostly harmless but noticeable.

Sometimes past repairs play a role. If someone patched something quickly 40 years back, that fix might give way now, leading to new cracks in the same place. And if your neighborhood has big old trees, their roots might shift the soil under your foundation, adding extra stress to old walls.

Here’s a table showing common causes and their effects:

Bottom line: if you spot cracks, you’re not alone. Most are just a sign your house has survived a lot. In the next section, we’ll check out what all those cracks actually look like and what they might mean for your home.

Types of Cracks You’ll See

Walk around any 100 year old house and you'll spot cracks in all shapes and sizes. Not all cracks are equal; some are harmless and others are red flags you shouldn’t ignore. How can you tell which is which?

The most common cracks you’ll find are:

• Hairline cracks: Super thin, less than 1/16-inch wide. Most of these show up in old plaster and around door frames. They’re often just from the house settling or from temperature swings.
• Vertical cracks: Often found in the walls, running up and down. These are usually due to natural settling or tiny shifts over decades. Unless they’re wide or growing, they’re usually nothing to stress over.
• Diagonal cracks: These start near window or door frames and angle up or down. Diagonal cracks can mean there’s some foundation shifting or a bit more movement than usual. Keep an eye on these, especially if they’re thick or changing.
• Horizontal cracks: These run side to side and are less common. In brick or basement walls, horizontal cracks can signal more serious pressure from the outside soil. These need a closer look from a pro.
• Ceiling cracks: Sometimes cracks show up where the ceiling meets the wall, or even across the ceiling itself. These pop up as the house settles, drywall or plaster changes shape, or if there’s been a roof leak at some point.

Here’s a handy table to get a quick idea of what each crack might mean:

One expert from This Old House puts it simply:

“Ninety percent of cracks in old plaster are cosmetic—but ignoring the ten percent that warn you of bigger issues can cost you big later.”

So, the important thing is not to panic at the first sign of a crack, but to know what you’re looking at. The next step? Figure out if your cracks are staying the same or getting worse over time.

When to Worry About Cracks

Not every crack means your old place is in trouble, but some cracks are bigger red flags than others. So how do you spot a real problem before it turns costly?

First off, pay attention to the size and shape of the crack. Hairline cracks—less than 1/8 of an inch across—pretty much come with the territory in any 100 year old house. But when you see a crack wider than 1/4 inch, especially if it keeps getting bigger, it's time to take it seriously.

Location also matters a lot. Here’s the quick lowdown on what to watch:

• Cracks running at an angle (usually 45 degrees) near doors or windows: These often signal movement in the foundation or framing.
• Horizontal cracks in basement walls: These are more worrisome than vertical ones. They can mean pressure is building up from the soil outside, putting stress on your wall.
• Stair-step cracks in brickwork: This pattern spells trouble, especially if it’s getting wider or the bricks seem out of line.
• Cracks by the foundation or uneven floors: If you notice doors sticking, windows that won’t open, or sloping floors, these symptoms paired with cracks could point to structural problems.

Here’s some useful data on when cracks become risky enough to get a pro involved:

If you ever spot cracks that grow fast, let in water, appear after a flood, or come with a musty smell, don't wait. Grab your phone and snap a picture, then call an expert. A local contractor or structural engineer can tell if it’s something minor or a big fix in the making.

How to Monitor Cracks

Keeping tabs on cracks in a 100 year old house isn’t hard, but it does take a bit of attention. Think of it like checking the oil in your car—even if nothing seems wrong, you want to be sure it’s not getting worse.

The best way to start is to document what you see. Grab your phone and take clear pictures of each crack you spot, making sure to get close-ups and some shots that show where they are in the room. This is way easier than trying to remember if that line in the plaster got longer after a few months.

• Use sticky notes or painter’s tape next to cracks so you track exactly which is which in your photos.
• Make a note of the date you took each picture. Set a calendar reminder to check again every three or six months.
• Sketch a simple layout of your room and mark where each crack is. No need to be an artist—this is just for your records.

If you want to get serious, put a pencil mark at the end of the crack and watch for it to grow past the mark. Some folks use a ruler or even a small piece of glass glued across a crack (called a crack monitor strip), but unless you’re really worried, you probably won’t need that level of detail.

Growth rate can tell you a lot. If a crack stays the same for a year or more, it’s likely an old issue that’s not active. On the other hand, if you see a crack that grows more than 1/8 inch in a few months, or new cracks keep popping up, it’s time to get a pro involved.

Don’t forget the context: a single ceiling crack isn’t as alarming as multiple cracks running from windows down to the floor. Structural cracks usually look diagonal or follow stair-step patterns in brick, while plaster cracks are often random. Keep your eyes open for any shifts in floors or door frames that start sticking too.

If you ever feel out of your depth or things change fast, that’s the moment to call a home inspector or a structural engineer. Otherwise, regular monitoring can help you stay on top of small problems before they get expensive.

Repair Tips and Prevention

If you spot cracks in your house and want to stay ahead of them, you can do a lot without calling in an army of contractors. Keeping an eye on problem spots and fixing small issues early saves money and stress later. Don’t ignore anything that looks suspicious, though—sometimes cracks are just old house character, but sometimes they signal a bigger problem.

First things first, figure out what’s actually normal for a 100 year old house. Hairline cracks under 1/16 inch wide—especially in plaster or along drywall seams—are usually nothing to lose sleep over. If the same crack has been there for years and hasn’t grown, you’re fine. Cracks wider than 1/4 inch, or ones that appear suddenly, need a closer look.

• For hairline cracks in plaster or drywall, you can use spackling paste or joint compound. Sand it smooth after it dries and do a quick repaint.
• With brick or masonry, cracks under 1/8 inch can be filled with flexible mortar repair caulk. Buy a color that matches your brick as close as possible for a clean look.
• If you’ve got a crack that keeps coming back, or doors and windows nearby are sticking, it’s smart to get a pro—preferably a structural engineer—to take a look.
• If it’s a moisture problem (like water stains or peeling paint), check your gutters and exterior grading. A little landscaping or gutter extension can steer water away from your house and make a big difference.
• Keep an eye on cracks through the seasons. Mark the ends with a pencil and take a photo now and then to see if they’re really growing or just holding steady.

Here are some quick stats and facts on old house repairs:

For prevention, stay on top of leaks and moisture. Keep gutters clear and downspouts aimed away from your home’s foundation. Make sure the ground around your house slopes away—just a couple of inches over ten feet helps. If you do a big remodel or have to cut into plaster, patch with a flexible compound so your walls can keep moving gently with the seasons, instead of cracking right away. Finally, don’t sweat every little crack. Old houses flex and shift, and that’s totally okay as long as you’re not seeing obvious signs of foundation trouble.