Two organizations that publish reference material on this exact question — a materials-engineering institute and a home-inspection association — largely agree on what to look at first.
Almost every foundation develops some cracking over time. Rather than rely on general folklore about crack widths, it’s worth looking at what the two organizations most directly responsible for documenting concrete cracking and home-inspection findings actually publish on the subject.
The core distinction: cause, not appearance
The American Concrete Institute’s Committee 224 report on concrete cracking draws a clear line between two categories: non-structural cracks, caused by internal stresses such as drying shrinkage, and structural cracks, which result from incorrect design, faulty construction, or overloading.[1] The same report notes that classifying a crack correctly is the necessary first step before deciding on a prevention or repair method — in other words, the crack’s cause determines the response, not how alarming it looks.[1]
What a crack’s shape tends to indicate
InterNACHI’s published inspection reference material — used in training licensed home inspectors — catalogs several recurring crack patterns and what they’re generally associated with:
Vertical cracks: InterNACHI’s materials note that a vertical foundation crack can indicate serious settlement if it is unusually large or actively moving, but is of less concern when the cause is ordinary shrinkage — and that vertical cracks are not caused by frost.[2]
Diagonal cracks: Diagonal cracks that grow in width — especially ones wider at the bottom than the top — are associated with settlement.[2]
V-shaped and inverted-V cracks: Two cracks forming a V shape are linked to heaving (especially alongside crushed mortar joints), while two cracks forming an inverted V or pyramid shape point toward settlement or drooping in the middle of a span.[2]
Horizontal and step cracks: InterNACHI’s photo reference gallery separately documents horizontal cracking linked to hydrostatic (water) pressure, and stair-step cracking as its own recurring category distinct from straight cracks.[3]
Why documentation matters even for minor cracking
Because InterNACHI’s material is written for licensed home inspectors rather than structural engineers, it’s also a useful reminder of scope: a standard home inspection can flag a crack pattern worth investigating, but determining the actual cause and whether remediation is needed is engineering work, not inspection work.
If a crack in your foundation matches one of the patterns above, a structural assessment can determine the actual cause — not just describe what it looks like.
Sources
- ACI Committee 224, American Concrete Institute, “Causes, Evaluation, and Repair of Cracks in Concrete Structures,” Journal Proceedings Vol. 81, Issue 3 — concrete.org
- InterNACHI (International Association of Certified Home Inspectors), foundation and structure training reference material — summarized via published study content at quizlet.com/518730049 (sourced from InterNACHI’s official course material)
- InterNACHI, “Settlement and Cracks” inspection photo reference gallery — nachi.org/gallery/settlement-and-cracks