As spring rapidly approaches here in New England and the snow starts to melt away, we are getting many excited and anxious calls about outdoor and especially stone wall projects. One of the questions that we are often asked is “What kind of a footing is required for my wall?” So we decided to post about footings.
A footing distributes the weight of the wall over a wider area, reducing the downward pressure of the wall’s weight. Basically, the footing transmits the load into the soil. Depending on various factors such as wall height, retaining requirements, architectural features, etc., either a concrete footing or a crushed gravel footing is usually used.
A solid concrete footing is mostly required for walls HIGHER than 4 feet. The concrete footing is typically reinforced with rebar, increasing the tensile strength of the concrete footing.
For walls LESS than 4 feet high, another much more economical type of footing – a gravel footing, can be used.
For a typical 4 foot retaining wall at NSWS, we usually recommend a 30 inch by 30 inch base filled and properly compacted with approximately 24” of crushed ¾”stone or gravel. The bottom of a wall should be below grade approximately 6” or 1/10th of the exposed wall height.
The general idea here is that any water that may penetrate the footing will travel through the crushed stone or gravel and allow the wall to remain stable. As long as a footing remains relatively dry during the winter months, there will be no differential settling caused from the infamous New England freeze and thaw cycles.
* Source: “Stonework: Techniques and Projects” by Charles McRaven