Construction Consulting Questions #3 - What does it mean when I see a horizontal crack along my foundation?
The horizontal crack that most people refer to along a concrete foundation is usually located at the base of the wooden foundation sill plate which is attached (or should be attached) to the concrete foundation. A wooden cripple wall or floor framing system is normally built on top of the wooden sill plate. Throughout most of the 1900’s up until the 1980’s or so, when stucco was applied as the exterior surface to a structure, the stucco was often toweled on down past the sill plate so that it adhered to the exterior face of the concrete foundation.
Adhering the stucco to the outside face of the concrete foundation was a common practice that made the stucco look flat and uniform at the bottom instead of being formed in or shaped back toward the sill plate which would then cause a visual protrusion so to speak.
The horizontal crack that is referred to by most people is more often than not caused by foundation rotation. When the soil that the concrete foundation is placed upon becomes wetter on the exterior side of the foundation than the interior side, the soil gets compromised “softer if you will” and then the outside bottom portion of the concrete starts to settle relative to the inside bottom of the concrete, and the concrete foundation then begins to rotate outward. As this occurs, the bottom of the wooden wall above the sill plate also goes outward causing a horizontal crack which we are referring to. However, the crack, as you are now beginning to see, is not a crack in the foundation at all but rather the displacement between the stucco adhered to the wooden wall (at the base of the wall) and the stucco adhered to the exterior face of the concrete foundation.
Prime suspects for causing foundation rotation, which in turn can create the visual horizontal crack, usually start with poor exterior surface drainage. Land which slopes toward the structure then creates a low area along and adjacent to the concrete foundation itself. Surface water, as well as, “or in addition to” the rain water which drains down the siding of the structure can thus end up soaking the soil and compromising it to the point where the concrete foundation actually starts to rotate. So there you have it, foundation rotation being more often than not, the cause for the appearance of horizontal cracking along the foundation(s) of a structure.
Anderberg Construction Consulting, Inc.
4100-10 Redwood Road #368
Oakland, CA 94619-2363
(510) 482-2779
tomanderberg@gmail.com
