Digging a Slab Foundation and Footings

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Digging and pouring your own slab foundation is the best option for a do-it-yourself project. These foundations are inexpensive, and easy to dig, pour and maintain. There are many different variations of the slab foundation, but for a home project, the monolithic approach is the best. Keep in mind that slabs are for small houses only, usually one-floor ranch models. While you will not have a basement, you will have added stability.

Things You'll Need

  • Backhoe
  • Shovel
  • Pick
  • Measuring equipment
  • Cement
  • Gravel
  • Wire mesh
  • Level
  • Install all plumbing fixtures prior to beginning the foundation. You will pour the concrete around these rough-in pipes. Brass piping is more resilient and durable than PVC for this type of job.

  • Measure the entire perimeter of the foundation. Put stakes in each corner of its shape, and line with chalk the connections that will make up the perimeter of the structure. The monolithic method of slab digging means that you will have to dig the perimeter deeper by about six inches at a minimum. So there are two projects: You need to excavate the center, but at the same time you also make the perimeter, about a foot wide all the way around, twice as deep at a minimum as the rest. You will then pour the concrete as a single slab, filling in the deep trenches as well as the shallower central part of the foundation. The size of the perimeter will be identical to the dimensions of the house.

  • Dig the foundation out with a backhoe. This might be contracted out to a professional for speed and accuracy. Smaller jobs, like a garage foundation, can be done by hand. You want an even hole for the central and side parts of the foundation. The backhoe should operate at the same time you or a crew member works on the ground to make sure the depth remains at the proper specifications. Never refill any parts of the trench even if they dig too deep.

  • Level out the central area of the foundation and the perimeter. These must be consistent throughout. Adding gravel and sand later on will help you level the soil. It should be close to perfection. Once the concrete is poured, you will use a level to make certain each section is consistent. Starting with a precise digging depth through the foundation will make that process easier.

  • Dig the foundation as deep as is required to reach compacted, strong soil. In most cases, you will have a soil analysis done prior to digging. In some states, this is required, and a surveyor will be able to mark the exact dimensions of the house. In most climates, the excavation for the central parts of the foundation are no more than four or five inches deep in the center, but it can get to six or seven inches in colder climates. These are then covered with sand, crushed rock or gravel to provide a base for the concrete. Normally, wire mesh or rebar reinforcements will be included to pour the concrete around for support.

  • Grade the sides of the newly excavated foundation. You want to direct water away from the structure, so the fill you have removed from the site can now be used to grade the sides away from the foundation. About 5 percent is the most you will need here, and it should be a fairly long taper, depending on how much room you have on the sides of the structure.

Tips & Warnings

  • Always take care when using professional digging equipment. If you are doing this yourself, make sure to read all manuals.
  • If your foundation hole is too deep, or deeper than necessary, this is not a problem. Covering it with a bit more gravel and using more cement later on would easily solve this problem.
  • Never use dirt you excavated to fill in any part of the hole if you think you've gone too deep. This soil is unstable and will force the structure to settle later on. Since it's been dug up, its no longer suitable for building upon. Rely on gravel or sand for any fill.
  • Err on the side of digging deeper than necessary. The more gravel you use to fill the foundation, the more stable the structure will be. Gravel serves to imitate stable soil with high load-bearing qualities.

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