[Editor’s note: This is the first part of a two-part story; it provides an overview of foundation layout and describes the author’s technique for building footings. See Part II here for the completion of the stem walls.]
While I was learning the trades in high school, the carpenters I worked with also built foundations; during one particularly busy period, we formed and poured 10 of them in a month and a half. We were working in a cul-de-sac, and would set up the footings for four houses at a time, then pour them all at once. It was tough work, but it taught me a lot about concrete. About five years ago, I began putting those skills to use again when our company stopped subbing out our foundation work. Now we form and pour all the footings and walls for the homes we build, using the same methods as most of the foundation subs in our area.
Foundation work isn’t for everybody. For one thing, it involves an investment in forms and other equipment. Over the years, the company I work for has accumulated about 120 2-foot-by-8-foot forms and an assortment of cut pieces. Currently, these 1 1/8-inch-thick MDO forms cost about $40 each, but we also occasionally find less-expensive used forms that are in good condition — usually from contractors who have been forced out of business. We probably have about $10,000 invested in forming materials and related equipment, though our only specialized tools (in addition to the forms) are rebar cutters, a site laser, and a few levels and trowels.
Being involved in a project from the bottom up keeps our crew busy and allows us to make sure that dimensions are accurate and earthquake hardware is in exactly the right place. This makes the carpentry much easier later on.
Layout and Excavation
The excavator and I begin each new construction project by meeting on site and staking out the hole. I depend a lot on my excavator’s experience to keep me out of trouble, especially under tricky site and soil conditions. We seldom have to dig very far, since the ground rarely freezes here and our minimum footing depth is only 12 inches.
Usually we just follow the terrain using common sense when determining the depth of the excavation. If we are trying to match the elevations of any nearby houses, we’ll take a number off a siding course or some other fixed point with our laser level and use that to establish a benchmark elevation. In most cases, though, we don’t work from a fixed benchmark; instead, we determine wall heights and other elevations from the top of the footing — the vertical rise method.
When the excavator cuts the hole, we make sure it’s large enough to fine-tune the location of the house’s footprint as we’re laying out forms. We stake the property corners and mark the property boundaries with strings, which we leave in place so that the inspector can double-check our setbacks.
