Building Foundations on Loose Stone Screen Rubble

About Loose Rubble Trenches

• A rubble trench uses materials that are commonly found and do not require a separate manufacturing process like cement does. This use of materials saves on energy that adds to construction costs and is therefore less polluting to the environment, as well. Frank Lloyd Wrights promoted the use of rubble trench foundations, using loose stone that was screened to a uniform size to create an even surface on which to construct his designs.

Advantages of Loose Rubble Trench Foundations

• Rubble trench foundations built with screened, loose materials act as a French drain, which draws the rainwater away from the foundation, as well as providing bearing for the grade beam that sits on top of the rubble to spread the weight of the building. Without the water settling around the foundation, less freeze-thaw heaving of the foundation occurs.

Building Rubble Trench Foundations

• For a rubble trench foundation, the trench is generally dug with a backhoe several inches below the frost line and sloped to allow for drainage. The rubble or gravel is then screened to a uniform size with an average of 1 1/2 inches, according to Down to Earth Design. A geotextile material may be used to line the trench to prevent silt from permeating the gravel and loosening it. The gravel is laid into the trench and then compacted. The gravel is then covered with a grade beam of concrete for a stable building surface. This beam is often steel-reinforced for additional strength.

Another Use of Rubble Foundation

• Another use of rubble for foundation material is the earthbag concept. With this techniques, a foundation material is created by packing the loose rubble into earthbags. Earthbags are woven polypropylene sacks that are filled with a mixture of sand, gravel, clay and cement. These are laid in several courses, or layers, and then compacted to create a solid foundation for building. These earthbags provide a more sustainable foundation material than a traditional cement foundation and cost no more than traditional cement foundations, according to EarthBagBuilding.com.