Frost Heave

Posted by in Foundations | January 24, 2013

January is the time of year when we occasionally get calls regarding a service door that is binding or a garage door does not close or open properly.  Subsequent examination of the situation often discloses that a portion of the wall around the door has lifted, thus distorting the rectangular shape of the opening.  Or we may get a call about a basement wall that has cracked horizontally and the upper portion of the basement wall has lifted.  A sudden appearance of these conditions in January and their improvement by March is a good indication that the problem is frost heave.

Frost heave is the vertical expansion of the soils caused by the formation of ice lenses as groundwater near the surface of the soil and/or under the footing or concrete slab freezes.  As the ice lenses form and expand they lift everything supported above.  A February 2013 article in Fine Homebuilding states that not only does the water in the soil freeze and expand, but unfrozen water below the frozen soil is drawn toward the ice lenses due to capillary action and vapor diffusion, causing the ice lenses to grow further.

We have observed frost heave to be more prevalent in areas where soil tends to retain water due to poor roof, surface, or subsurface drainage.  We have also noticed that frost heave is more common when ambient temperatures are 10 degrees Fahrenheit or lower for an extended period of time.

Concrete pavements are very susceptible to lifting by frost heave due to their shallow depth of soil support.  And, if the concrete pavement was not isolated from a basement wall, garage wall, etc. with an expansion joint, the concrete pavement often remains bonded to the face of the wall and lifts the wall off its foundation when it is lifted by the ice lenses.

The effects of frost heave are well demonstrated by poorly installed fence posts, that is, posts with a shallow bearing depth.  The posts are lifted by frost in the winter and drop back down partially and non-uniformly in the spring and summer when the frost melts and the soil dries.  The result is an uneven fence line that pitches up and down rather than following the line of the grade.  This pattern of movement can occur in the walls of buildings also.

Data from the observations of historical frost depths has allowed local jurisdictions to specify a minimum depth for foundations.  The minimum depth is usually called the frost line (42 inches for Northeast Ohio).  Setting the bottom of a wall or fence post footing below the frost line will greatly reduce the risk of damage from frost heave. So, save yourself some trouble and build using the experience gained from those who have gone before us.