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Archive for the tag “differential”

Three Common Causes of Differential Foundation Movement

Hello everyone, I hope you guys have been doing well. I’ve been a bit busy lately, but now that I’m caught with my work and various other stuff, I have decided to continue with the theme of foundation movement.  Last time, we talked about cracks in the finishes of the house – I would like to now move onto some of the root causes of the foundation movement.

At its most basic level, most foundation movement is caused by change in the moisture content and resulting expansion/contraction of the soil supporting your house foundation.  Depending on the amount of clay or fill soil on your property, the resulting differential movement can vary by location and magnitude.  In some other cases, it is a failure of the foundation structure; it is far less common and in most cases associated a pier and beam foundation.  Even then, most of those failures I’ve seen were affected in some way by moisture content of the air/soil within the crawlspace.  Having said all that, today I will discuss the effect of soil moisture content as it is the prevalent cause of foundation movement.

Tree Roots within the Vicinity of the Foundation

The most common cause of foundation movement I see is the result trees affecting the moisture content of the surrounding soil.  In times of relative drought, the tree roots will absorb more water in the soil and decrease the relative moisture similar to surrounding areas.  In times of more rainfall, the dry soil will then expand and change the relative soil level again.  In general, tree roots extend an additional 50% further from the trunk than the outer canopy.  If the tree roots extend under your foundation, the soil under your foundation will expand differentially to surrounding areas depending seasonal rains.  The cracks resulting from this foundation movement will typically expand and contract, or reopen when patched.  Differential movement associated with tree roots can be reduced by placing a root barrier around your foundation and maintaining a regular watering program around your house.

Site Drainage

As with the trees, various site drainage conditions can cause water ponding and result in different soil moisture contents around your foundation.  As a result, the soil in areas with increased amounts of water will expand more than the soil in other areas.  Similar to the tree rot conditions, the level of the foundation and resulting cracks will fluctuate depending on the amount of seasonal rains.  Differential foundation movement associated with site drainage can be reduced by maintaining an adequate slope around the perimeter of the foundation so that the site drainage will allow water to flow around and away from your house.

Plumbing Leaks

Water from plumbing leaks can also cause the expansion of soil, typically within an isolated area.  Depending on the size and frequency of the leaks, the leaking water can cause differential foundation movement and result in interior distress associated with that movement.  In most cases, the soil expansion and differential movement does not extend far from the leak location and will not result in wide spread foundation movement.  In addition, the soil will typically contract back to it’s original volume once the leak is repaired.

Given this short outline, I hope that you can get a basic idea of what is causing the differential foundation movement you are having and how to address the issue.

What has been your experience been like in dealing with differential foundation movement?  For the people inspecting foundations, I’d be interested in hearing about your stories as well, since I still definitely have a lot more I could learn on the topic.  If you enjoyed my post, hit the like button, follow my blog for updates and share this post with your friends.  Thanks for reading and have a good week!

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