138 Chapter 6
Foundations are usually constructed of continuous footings, pilings, or grade beams. Continuous or
spread foundations are commonly used in residential and light-commercial construction. This type of
foundation is based on a footing and wall. Concrete footings form the base of the foundation system and
are used to displace the building loads over the soil. Piling foundations are typically used when conven-
tional trenching equipment cannot be used safely or economically. Piling is a form of foundation system
that uses columns to support the loads of the structure. They are rarely used for residences or low-rise
commercial buildings. Grade beams are reinforced-concrete beams positioned at grade (ground) level
below the stem wall to provide a bearing surface for the superstructure. They can be used in place of
the foundation to provide added support for a foundation in unstable soil.
Figure 6.13B Sections through a two-story residence.