The first step in installing a foundation is to mark out and install the footings. The footings are a continuous band of concrete, about a foot thick which runs under the foundation walls. The purpose the footings is to distribute the weight of the walls to a larger surface area to minimize any settling. Usually footings are 2 feet wide, but my contractor likes to make his 3 feet wide.
Using lasers as a guide, the contractor drives stakes into the ground, representing each outside corner of the foundation. This, of course includes all the jogs and angles of the walls. Then, for more accuracy, he drives a nail into the top of each stake so each corner is exactly marked.
Once the foundation walls are marked, more stakes are driven, this time creating a line 1 foot to the outside of the foundation walls and one foot to the inside. This represents where the footings go. The dirt is dug out to a 1 foot depth and forms are laid. Accuracy isn't too critical at this stage. If the forms are off by a couple of inches either way it won't make too big of a difference. The height if the forms is important, but not critical. So long as the top of the forms are about 1 inch above the final footing height, all is fine.
Once the forms (BTW, the "forms" in this case are merely lengths of 2 x 12's) are all set, 3 pieces of reinforcing bars (rebars) are placed inside to reinforce the footings. The rebars are set on top of bricks to keep them in the air to ensure that they'll be embedded in the footing later.
In New York, it's that law that footings must be at least 3 feet below the final grade. If they weren't, when the ground freezes in winter, it would expand, lifting the house. It doesn't' take many cycles of freeze/thaw to do real damage to the structure. The depth of the footing, of course, varies with the climate of the area. I mention this because we're having a side entry garage, which is at basement level. So here, the footings needed to be another 2 feet deep. When I came to the job site after all the forms were set, I noticed this was not the case, so the contractor had to make them deeper. This is why constant checking up is necessary when building a house.
Once the forms are in and the rebar is set, a final level line must be established so the tops of all the footings are at the exact same level. Here again they use a laser level. Here's how it works: First they set up the level on a tripod where it won't be disturbed. Then they take an electronic receiving device and attach it with a clamp to a 4 foot stick. After some calibration, all the worker has to do is place the stick against the inside of the form and move it up and down as he listens. As the laser gets close to the correct mark on the receiving device, it starts to beep. When the stick is at the exact height, there is a continuous tone. At this point the worker takes a nail and drives it onto the side of the form, just under the 4 foot stick. Repeat the above operation about 200 times and you've got a perfectly level line throughout.
Besides the wall footings, there are also a number of "piers" that need to be set. The piers act like footings in that they distribute weight, but instead of a wall sitting on them, there will be lally columns. The lally columns will later support the steel that will be used as the main beams of the house. The plans called for the piers to be 3 foot square x 18 inches deep, but I decided to make them 4 foot square at the last minute.
The final step is to oil the forms. Oil is necessary to make it easier to strip the forms away from the dried concrete later on. The oil is applied with an industrial bug sprayer. Now we're ready to pour the footings!
