While the crack you just noticed may have been opening slowly over a period of months or years, and it became big enough to catch your eye only recently, it is also possible that it appeared in a single day.

    The key word for understanding how a fairly large crack can appear overnight is “elasticity.” While we normally think of things like rubber bands as being elastic, all materials--including concrete, brick and mortar--have a small amount of elasticity. Within that elasticity is the ability to contain the tension (pulling-apart)  forces imposed on them—up to a point.

    But, like a over-stretched rubber band, when the forces pulling building materials apart exceed a certain point, they “snap” and a crack opens all at once. People in homes with extreme pressure being applied to the structure, from sink hole activity or clay soil heaving, sometimes actually hear the sounds of their walls fracturing. But mostly it’s not that dramatic.

   One thing to try to determine after a crack appears in the walls or floor of your home is whether it is a one-time event or will continue to open up. A simple device called a crack monitor can help you determine what is going on. It consists of a plate with a grid printed on it that is placed over the crack and secured at one side, and a clear plastic plate with a cross-hair on it, which aligns exactly with the center of the grid at time of installation, that is secured overlapping it at the other side of the crack.  

    Keeping tabs on the monitor will tell you if any further movement is occurring and, if so, at what rate. We keep a couple in the truck for installation where a homeowner is concerned about cracks they have found. 

    Also, see our blog post How do I recognize serious structural problems in a house?

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To learn more about exterior walls and structures, see these other blog posts:

• What is the average lifespan of a house foundation?

• What causes vertical cracks in fiber cement siding planks?

• What causes raised white lines of residue on a block wall that are crusty and crumbling? 

• What is the difference between soil subsidence, heave, creep, and settlement? 

• How much ventilation is required for the under-floor crawl space of a home? 

• What causes stair-step cracks in a block or brick wall?

• What causes a horizontal crack in a block or brick wall? 

• How can I tell if a diagonal crack in drywall at the corner of a window or door indicates a structural problem?

• What causes the surface of old bricks to erode away into sandy powder? 

• What are the pros and cons of concrete block versus wood frame construction?

• Should I buy a house with a crawl space? 

• Why is my stucco cracking?

• There's cracks running along the home's concrete tie beam. What's wrong? 

• What would cause long horizontal lines of brick mortar to fall out?

• What is engineered wood siding?

• Should I buy a house that has had foundation repair? 

• What is a "continuous load path”?

• Should I buy a house with asbestos siding?   

• How can I tell if cracks in the garage floor are a problem or not? 

• What do you look for when inspecting vinyl siding?

• Why is housewrap installed on exterior walls under the siding? 

• Why did so many concrete block homes collapse in Mexico Beach during Hurricane Michael? 

• How can I tell if the concrete block walls of my house have vertical steel and concrete reinforcement?

• Should I buy a house with structural problems? 

• What are those powdery white areas on my brick walls?

• What causes cracks in the walls and floors of a house?

• How can I tell if the exterior walls of a house are concrete block (CBS) or wood or brick?

• What are the common problems of different types of house foundations? 

• What are the warning signs of a dangerous deck?

• How can I tell whether my house foundation problems are caused by a sinkhole or expansive clay soil?

        Visit our EXTERIOR WALLS AND STRUCTURE page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.