Footings and Excavations

Shallow Foundation

Footings

  The size and dimension of the footer are based on soil characteristics. Soil and subsoil in their natural state are often sufficiently stable to support light frame construction, the average load bearing capacity for undisturbed soil is 2000 pounds or greater, per square foot. Where building code permit;today modern home builders, in light frame construction build houses using a form type called Earth-forms, simply on an excavated surface, cleared of vegetation, foliage, etc. A trench is dug out according to the footer specifications, say for example the frost-line is at one foot, so you know the footer dimension for a 8 inches thick wall is going to be 16 inches wide by 8 or 12 inches deep, dependant upon soil characteristics, but 8 inches deep is standard thickness, I've heard of 6 inch footers this might be ok for a garage pour but I would never use anything less and neither should you or you'll be asking for trouble. Refer to the blue prints.

  Your trench depth would be 1 foot for frost-lineplus 8 or 12 inches for the footer, so your trench depth would be 32 or 36 inches. That's 8 or 12 inches for the footer 12 inches below the frost-line plus one foot of soil to the surface, or grade, so our trench would be 32 to 36 inches at the the highest point of the natural grade.

  Then your trencher will dig your earth-form 32 to 36 inches deep by 16 inches wide or more and keep a level dig to complete the earth-form.

  From the blue prints the height of your batter board represent the top of the finished foundation wall. If we use the example above it would take two courses of cement block to bring the foundation wall to grade and another two to three courses to the building lines or finished foundation wall. Your underground utilities are marked, staked and stubbed your trench dig will come within two feet of the underground and stubbed utility line and since most of these are buried including the telephone and television cables as well contact with a company representative will alleviate the problem of accidental damage to these lines. The rest will be hand dug to prevent damage by heavy equipment.

Excavations

  Some builder's like to put in temporary batter-boards and stake the approximate location of the excavation so the backhoe or bulldozer operator can perform the dig before the exact building lines are set. This is an extra step to the process but it eases the burden from the equipment operator by giving him latitude in movement and should result in greater precision.

   Then go back and set the exact location for the building, it's a matter of what is expedient at the time, however, the lines have to be taken down before this operation. Once the lines are down the digger can start digging. Make sure the soil is piled a good distance from the excavation, when you go back to hang your lines, dirt piles won't have to be hand shoveled away from the path of the lines. The operator will dig approximately two-feet or more beyond the building perimeter to allow for pipes, drainage and work space.  On a clay or cohesive type soil you'll need slight fer-ring back depending on the depth of the dig and on loose or sandy soil types, you'll cut the slope back at a 45 degree angle to prevent cave-ins.