About the Foundation
The foundation is a home's infrastructure. It supports the floor, wall, and roof framing. Moreover, the foundation helps keep floors level, basements dry, and, believe it or not, windows and doors operating smoothly.
The foundation is also an anchor of sorts. This can be especially important if your home is built on anything other than flat ground or is in an area prone to earthquakes.
Interestingly, the origin of many leaks and squeaks can be traced to the foundation. A cracked or poorly waterproofed foundation, for example, can result in excess moisture in a crawlspace or basement. Without adequate ventilation, this moisture can condense and lead to, at best, musty odors, leaks and squeaks, and, at worst, rotted floor framing.
If your foundation is built of brick, be sure to read the sections on dealing with efflorescence, moisture control, grading and drainage, and especially tuckpointing. If your brick foundation is not reinforced with steel or is crumbling, you should immediately consult a structural engineer to determine what means can be used to improve the integrity of the foundation. (Although this goes beyond the scope of home maintenance, you should be aware that an unreinforced brick foundation that is in good condition can be reinforced by capping the foundation with concrete reinforced with steel.)
If your home was built after the 1930s, chances are good that the foundation consists either of poured-in-place concrete (grade beam), concrete block, or a concrete slab. The latter has become especially prevalent in the last couple of decades by builders seeking to cut costs and create more affordable housing.