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Photograph of a cracked concrete slab, cracks around a Lally column How to Distinguish Settlement Cracking from Frost Heave in Concrete Foundations, Walls, Floor Slabs

  • SETTLEMENT vs. FROST HEAVE CRACKS - CONTENTS: How to distinguish frost heave cracking from settlement cracking in concrete foundations, walls or floor slabs. Photographs of types of poured concrete slab cracks. Poured concrete crack diagnosis for concrete slabs and concrete floors
  • POST a QUESTION or READ FAQs about t how we tell the difference between building settlement & frost heaves
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How do we tell the difference between foundation or slab settlement & foundation or slab frost heaves?

This article describes how to distinguish frost heave cracking from settlement cracking in concrete slabs - a division of our article on How to Identify and Evaluate Settlement Cracks in Slabs in Poured Concrete Slabs or in concrete floors in basements, crawl spaces, or garages.

This article series describes how to recognize and diagnose various types of foundation failure or damage, such as foundation cracks, masonry foundation crack patterns, and moving, leaning, bulging, or bowing building foundation walls.



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Concrete Slab Settlement Cracks Compared with Frost Heaves in Poured Concrete Slabs

Frost heaved concrete (C) Daniel FriedmanWhere cracks appear in slabs in homes built in freezing climates, it can be difficult to distinguish between frost heaves and settlement since both types of movement can cause similar cracking in a slab or foundation.

Our photo (left) shows frost-heaved poured concrete, in this case located outdoors. But these conditions can occur indoors too if heat is lost to a building, and especially if there is water, moisture, or a clogged drain line below a basement or floor slab.

We often find frost heaves too at garage floors near the garage door.

Types of foundation cracks, crack patterns, differences in the meaning of cracks in different foundation materials, site conditions, building history, and other evidence of building movement and damage are described to assist in recognizing foundation defects and to help the inspector separate cosmetic or low-risk conditions from those likely to be important and potentially costly to repair.

Clues suggesting settlement cracks in a concrete slab

Clues suggesting frost heaved cracks in a concrete slab

Frost heave cracking is likely to be cyclical unless the building has gone through less than one cycle of seasons. Frost heave cracking can often be reasonably postulated as a cause or main factor in slab cracking if the inspector can identify site conditions that make it likely that there has been water around and under the foundation or slab, and that freezing conditions have occurred.

Photos of Frost Heave Cracked Basement Slabs in Older Homes

Cracked slab from water and frost (C) Daniel FriedmanA classic example of slab cracking due to frost heaving can be seen in some older homes (1885-1935) in which roof drainage was routed from gutters down into the home to a drain that ran under the basement floor slab and thence out to a storm drain in the street (urban houses).

Our photo (left) shows a frost heaved and cracked basement floor slab in a New York Home. A combination of loss of heat and lots of water below the slab caused the cracking around the Lally column and in other basement locations. In this case the floor (and the Lally column that was sitting on the concrete floor, not on its own independent pier) heaved upwards.

Watch out: you might see similar crack patterns around a Lally column that is settling due to a missing or inadequate pier. It's simple: is the floor heaved upwards (convex) or has it settled (concave). Or is it cyclical, heaving up and down as water levels and winter temperatures vary?

In such homes you may find that the basement floor slab is seriously broken up and heaved, some sections pushed several inches into the air, along either side of a rather straight line which tracks exactly the route of one of these buried drains. [We regret we didn't take photos of this - if any readers have photographed this condition please let us know.]

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