Cracks in Basement Floors

Contributed by Bill Huminski, Project Manager for SIR Development

Some home buyers are concerned when they see cracks in the concrete floor in the basement of a new construction home. However, it is important to understand that some cracks (straight ones perpendicular to the foundation walls) are intentionally installed by the foundation contractor to achieve the proper expansion controls of the basement floor. In the Northeast, basement floors are typically formed with poured concrete which expands and contracts with the weather. Concrete is at the largest volume when freshly poured and thus when cured has a tendency to contract. For this reason, concrete basement floors will shrink, expand and ultimately crack unless there is controlled expansion. Typically, expansion joints or plastic “zip strips” are placed perpendicular to the foundation wall at various points in the freshly poured slab to control the slab’s expansion. Without these controlled expansion joints, expansions cracks will form haphazardly throughout the concrete slab and cause damage. It is noted that this article generally deals with straight line cracks but it is always advised to have an independent home inspector confirm that any basement cracks are intentional “controlled expansion cracks”.

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