3. Digging the Foundation for the Three-Story Section of the House

The footings are obviously a critical part of the construction process. They ultimately hold the house up. In this area of Mexico they are traditionally made from local materials of stone and concrete. We'll be using rebar and concrete on the three story section and rock and concrete on the two story section.
There are multiple issues that factor in to deciding on the depth of the footing for a structure, and what type of materials to use.
Soil conditions are a big factor - as in what type of soil it is and how it changes through the course of the year due to climate conditions / weather.
The type of construction is important - what is the house built with and how many floors it will have.
In our case, the soil is clay. The temperature here varies between 45 and 85 degrees Fahrenheit. There is a rainy season of several months when the surface clay becomes slippery and viscous and a dry season when it is contracted and very hard a difficult to penetrate. These conditions require a fairly deep footing as the bearing capacity of clay is lower than that of a substrate such as sand or gravel.
The house we are building is one half three stories and one half two stories so we'll be building the foundation in two stages. This video goes through the dig for stage 1, the three story section of the house. The depth of the footing below the first floor is around six feet.
Details about a foundation can be computed by a structural engineer. How wide and deep it needs to be is figured out using the bearing capacity of the soil and the live and dead load it will bear. Width and depth of foundation calculated on the basis of safe bearing capacity of soil, type of soil and all the live and dead load coming on it. Guessing is probably not a good idea.

[@alisondblake]

Looking great!