Retaining Wall Height

• The height of a retaining wall is calculated from the bottom of the wall, to the top of the wall, or its finish grade. The exposed wall height is the distance between the grade on the low side and the top of the wall. The exposed wall height doesn't include the portion of the wall below grade, called the footing. The structural components need to support the entire height of the retaining wall.
  
  

Gravity Walls

• Gravity retaining walls rely on weight to resist lateral pressures from the volume of the soil being retained. The wall is about one-half to three-quarters wider at its bottom than its top for added stability, and it angles, or batters, back towards the soil as the wall rises. The batter increases the resistance to overturning. Gravity walls are recommended for heights up to 10 feet, but more material is needed as the wall gets higher.
  
  

Footings and Surcharge

• A footing helps prevent foundation failure and overturning of the wall. When a footing is attached to a retaining wall, the wall becomes a cantilever wall design. The wall and footing are sized according to the loads from the weight of the soil and other factors such as surcharge. A surcharge is a vertical load that might impose lateral pressure in addition to the soil being retained. A solid fence or wall attached or adjacent to the retaining wall may impose a surcharge when buffeted by the wind.
  
  

Building Permits

• Generally, building permits are not necessary for concrete retaining walls with a total height of 4 feet or less, when the retained soil is level with the top of the wall, and there is no fence or structure adding weight. Walls higher than 4 feet, or ones with the additional pressure, have more complex structural requirements -- requiring consultation with an engineer. It may be more economical to add a footing to a shorter wall instead of constructing a heavier gravity wall, if conditions call for stronger support.