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Cracking Up: A Brief Guide to Understanding Building Cracks

Writer's picture: James BrowneJames Browne

Have you noticed cracks in your walls and started wondering if your house is about to sink into the abyss? Don’t panic just yet! This guide will help you differentiate between cracks caused by subsidence or foundation movement (serious stuff!) and those due to other, less alarming reasons (like your house’s version of laugh lines).

                             

What Causes Cracks in Buildings?

Cracks can appear for various reasons, ranging from natural settling to soil movement under your foundation. Here’s a quick look at the main culprits:


Subsidence or Foundation Movement: The ground beneath your house shifts, taking your foundation on an unexpected ride.


Non-Structural Issues: Normal wear and tear, drying plaster, or a bit of seasonal stretching.

                


Cracks That Might Be Serious (Subsidence or Foundation Movement)


They’re Big and Bold

Width: Wider than 3mm (the width of a typical coin or a credit card slot).

Location: Near windows, doors, or corners of your house.

Pattern: Diagonal or stepped, following the lines of bricks or mortar.


They’re Persistent

Cracks that keep growing or widening over time are a red flag.


Things Aren’t Lining Up

Doors and windows become stubborn, refusing to open or close properly.

You might notice gaps where walls meet ceilings or floors.

Example:

A diagonal crack running from the corner of a window toward the floor outside could indicate your foundation is settling unevenly, causing subsidence.



Cracks That Are Just Cosmetic (Not Due to Foundations)


They’re Small and Shy

Width: Less than 3mm. Think hairline cracks that you’d barely notice unless you were looking for them.

 

They’re Random or Straight

Non-structural cracks are more likely to be straight or randomly patterned.

 

They Stay Put

These cracks are stable over time and don’t grow larger or longer.

Example:

A vertical crack in plaster near the corner of a room could simply be the result of normal drying after construction or seasonal temperature changes.

 


Key Differences Between Serious and Non-Serious Cracks


Feature

Subsidence/Foundation Movement

  Non-Structural Issues

Width

Wider than 3mm

       Less than 3mm

Pattern

Diagonal, stepped

       Straight or random

Location

Near doors, windows, or external walls

       Internal walls, plaster

Progression

Grows over time

      Stays the same

Associated Issues

Sticking doors/windows, gaps in frames

None, just a cosmetic annoyance



DIY Crack Detective Tools



A Coin or Credit Card: Measure crack width. If it’s wider than the card slot, it’s time to investigate further.


A Level: Check for uneven floors or tilted walls.


A Notebook: Track crack changes over time. Are they growing? Multiplying? Stay vigilant.


 

When to Call in the Experts

If you see any of the following, it’s time to call a structural engineer or surveyor:

Cracks wider than 3mm or growing over time.

Cracks appearing along with other issues like sticking doors or sloping floors.

Cracks in external brickwork that are stepped or diagonal.


 

Final Thought: Don’t Crack Under Pressure!     



Cracks in buildings can look intimidating, but not all are cause for alarm. By understanding the differences between serious and non-serious cracks, you can decide whether it’s time to call in the cavalry or just a painter. Your house is tough—it’s built to last, even if it’s sporting a few wrinkles here and there!                                      

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