How to Design a Building Foundation


When you construct any type of building, the foundation is critical for supporting the structure over time. An important decision to consider is whether or not the foundation should become basement space. The foundation's costs may not be significantly more to include a basement. In the future, you can build extra rooms in the basement. Regardless of its practical aspects, a foundation can add to the beauty of a building or detract from it. For example, a brick-covered home foundation improves the look of the house, while a bare cinder block foundation can hurt the appearance.

Things You'll Need

  • Basic floor plan
  • Soil tests
  • Concrete
  • Cinder blocks
  • Metal wire gridwork
  • Gravel
  • Wood framing
  • Decide if your building needs a concrete slab foundation, a short crawlspace or a full basement. Hire experts to do soil testing, since a high water table will rule out basement construction. Sketch the dimensions of the building to define the exact depth the foundation will be. Allow 2 to 3 feet minimum for a concrete reinforcement wall around the circumference of the foundation to hold a slab concrete pour roughly 18 inches deep in the middle.

  • Design a slab for major strength. Build framework with wood and metal to hold the concrete pour. Use 1/2-inch plywood supported by stakes driven on the outer perimeter. Construct the box to hold concrete approximately 15 inches deep for every 8 feet of building height. Plan to install metal wiring, called rebar, in the concrete walls. Roll out metal gridwork to reinforce concrete making up the slab component.

  • Plan a crawlspace by digging ditches for footings around the perimeter of the building. Pour concrete for the footings. Lay cinder blocks on top of them for a crawlspace or basement. Leave room for a crawlspace door. Design the crawlspace to be approximately 4 to 5 feet high. Cover the dirt floor with plastic sheeting to keep moisture down.

  • Design a full basement with a concrete floor. Install drains in the basement plan to accommodate overflow from a washing machine or plumbing issues. Finish the concrete floor somewhat lower in each drain area. Trowel the concrete down about 2 inches lower around a drain. Consult a plumber to install all of the drain pipes before the concrete floor is poured.

  • Build a full basement by constructing the footings just like a crawlspace. Do allow a minimum of 8 feet of height in the center of a basement, however. Plan this height to begin at the top of a concrete floor you will pour. Pour the concrete floor at least 1 foot thick. Install floor joists and wooden framework for the building on top of the highest cinder block, leave the blocks open on top (versus capped). Attach wood to block using special anchor bolts.

Tips & Warnings

  • Draw openings for basement windows and a walk-out door in the drawings of the foundation. Each window and door will need a special overhead beam to support the expansion. You can purchase these beams, known as concrete lintels, when you order blocks for the basement construction.

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