The Importance of Foundation Grading and Drainage

The Importance of Foundation Grading and Drainage
 
It is generally understood that water flow toward a house foundation is not good, as it is likely to lead to water penetration concerns.  What is less frequently understood by most homeowners is that poor grading can also lead to structural concerns.   
One grading-related structural concern potentially affecting residential foundations is the result of excessive lateral (horizontal) pressure from the earth acting against the wall, particularly when the house has a basement mostly below grade or located on the side of a hill.  Besides supporting the weight of the house, the foundation wall functions as a retaining wall to resist the forces of the soil and water acting on it.  These forces are transferred through the wall to the floor structure above and a footing below – similar to how a beam or floor joist supports the loads acting on a house floor, only in a different direction.   
The foundation wall must have adequate strength to withstand the forces acting on it or it will shift and possibly crack.  This means the foundation must be designed and constructed to carry the vertical house loads, as well as the horizontal load of the particular type soil conditions present and other external forces. And in most cases it is, or at least initially.  But as time passes, the soil around the foundation may settle, allowing water to accumulate. This water contributes to the soil weight and resultant pressure on the wall.  
Changes in landscaping, tree growth, erosion on a hillside, remodeling work, and construction on adjacent properties are other conditions that can change water runoff patterns and ultimately direct more water toward a foundation.
 
 
When a foundation (or retaining wall) wall is overloaded from this redirected water and the resultant saturated soil, it may eventually move laterally, with a horizontal crack as the first indication.  While all foundation walls are subject to this type movement from lateral forces, older unreinforced concrete block masonry walls are particularly vulnerable, with the cracking most often showing up at the weakest point, the mortar joints. The deeper the foundation, the greater the forces acting on it.  Fortunately, there are ways to avoid any problems or correct then if needed.  
To help avoid excessive external pressure against a foundation, the property and foundation grading and drainage must be maintained to help direct water flow around and away from the foundation. Within the first few years after a home’s construction, it is not unusual for the backfilled soil to settle around the foundation, creating low areas where water may pond. Homeowner should periodically check for any changes in the grade level around the foundation and take steps to improve it when needed to ensure a positive flow of water away from the foundation.
 
 
While the grade at the foundation may need to be improved for drainage purposes, the soil should not be built-up so much that the soil or overlying mulch is close to or in direct contact with the siding, which can lead to decay or insect infestation. If a positive slope away from the foundation cannot be provided, it may be necessary to do some more extensive work on the grading and site drainage systems.  In some cases, window wells with underground drains may be needed. 
 
Note: These tips are only general guidelines. Since each situation is different, contact a professional if you have questions about a specific issue